Electric fishes of the genus Sternarchorhynchus
(Teleostei, Ostariophysi, Gymnotiformes); phylogenetic
and revisionary studies
CARLOS DAVID DE SANTANA? and RICHARD P. VARI FLS*
Division of Fishes, Department of Vertebrate Zoology, MRC-159, National Museum of Natural
History, PO Box 37012, Smithsonian Institution, Washington, D.C. 20013-7012, USA
Received 6 May 2008; accepted for publication 6 March 2009
Analysis of 88 characters of external and internal body systems yielded a phylogenetic reconstruction of the
Neotropical electric knifefish genus Sternarchorhynchus (Apteronotidae; Gymnotiformes). The results support a
hypothesis of Sternarchorhynchus as the sister group to Platyurosternarchus. A series of synapomorphies, many
involving major innovations of the neurocranium, jaws, suspensorium, and associated systems that permit an
unusual mode of grasp-suction feeding, support the monophyly of both genera. Synapomorphies largely resolve
relationships within Sternarchorhynchus with basal nodes strongly supported by characters pertinent to prey
capture and initial processing of food items. These possible key innovations may provide Sternarchorhynchus with
a competitive advantage over other clades of the Apteronotidae and account for the species diversity of the genus
in Neotropical rivers. Adaptive radiation in Sternarchorhynchus was analysed. Habitat preference transitions
repeatedly occurred in the genus between deep-river channel dwelling species and rheophilic species with
preferences for higher energy setting including rapids and swift-flowing fluviatile settings. Twenty-two species of
Sternarchorhynchus are described as new based on samples that originated in the smaller rivers draining into the
Golfo de Paria, the Marowijne and Essequibo River basins, the R?o Orinoco and in particular the Amazon River
basin. The 32 species in Sternarchorhynchus make it the most speciose genus in the Apteronotidae.
No claim to original US government works. Journal compilation ? 2010 The Linnean Society of London,
Zoological Journal of the Linnean Society, 2010, 159, 223?371.
doi: 10.1111/j.1096-3642.2009.00588.x
ADDITIONAL KEYWORDS: adaptive radiation ? Apteronotidae ? cladistics ? convergence ? key innovation
? new species ? osteology ? South America.
INTRODUCTION
Electric knifefishes of the genus Sternarchorhynchus
are tube-snouted, elongate, distinctly laterally com-
pressed fishes with a broad range in many Atlantic
drainages of South America. Sternarchorhynchus
ranges from the R?o Orinoco basin in Venezuela and
Colombia (Mojica, 1999; Lasso et al., 2004a, b) south
through the rivers of the Guianas (Planquette, Keith
& Le Bail, 1996; Meunier, 2004) and the Amazon
basin (Goulding, Leal Carvalho & Ferreira, 1988;
Cox-Fernandes, 1999) to the upper Rio Paran? in the
R?o de La Plata basin (Britski, Silimon & Lopes, 1999;
Campos-da-Paz, 2000). The genus is unknown from
the trans-Andean and Caribbean versant portions of
South America, the rivers of north-eastern and south-
eastern Brazil that drain directly into the Atlantic
Ocean, all portions of the R?o de La Plata basin
exclusive of the upper Rio Paran? system, and the
entirety of the southern reaches of the continent.
Sternarchorhynchus species are moderate-sized
predators (150 to 540 mm maximum total length) of
benthic invertebrates (Goulding et al., 1988; Marrero
& Taphorn, 1991). Their electrogenic abilities
*Corresponding author. E-mail: varir@SI.edu
?Current address: Programa de P?s-gradua??o em Gen?tica.
Conserva??o e Biologia Evolutiva, Instituto Nacional de
Pesquisas da Amaz?nia, Av. Andr? Ara?jo, 2936 Manaus,
AM, 69060-001, Brazil; and Laborat?rio de Fisiologia
Comportamental e Evolutiva, Instituto Nacional de
Pesquisas da Amaz?nia, Av. Andr? Ara?jo, 2936 Manaus,
AM, 69060-001, Brazil.
Zoological Journal of the Linnean Society, 2010, 159, 223?371. With 77 figures
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
223
facilitate the location and capture of prey in soft mud
and within the interstices between leaf litter and
other detritus (Marrero & Winemiller, 1993; Cramp-
ton & Albert, 2006). Similarly they hunt for and
capture aquatic insects, especially of the Chironomi-
dae, Ephemeroptera, and Trichpotera, in small spaces
in the river bottom and the tunnels and spaces in
compacted clay nodules (Marrero, 1987; Marrero,
Castillo & Machado-Allison, 1987; Marrero & Wine-
miller, 1993). Correlated modifications of the bones,
musculature, and other soft tissues of the jaws, and
suspensorium in the highly restructured, tube-like
snouts, and anterior portions of the neurocranium
allow extraction of prey items from these constricted
refuges (Aguilera, 1986). These restructurings permit
what has been termed ?grasp-suction? or ?suction
assisted by mechanical grasping?. Morphological
adaptations permitting this highly specialized feeding
mode are unique to Sternarchorhynchus and the
African mormyriform genus Campylomormyrus
amongst orders of fishes entirely restricted to fresh-
waters (Marrero & Winemiller, 1993; Winemiller &
Adite, 1997).
A diversity of secondary sexually dimorphic fea-
tures characterize genera in the Apteronotidae, with
these modifications most prominent in the morphol-
ogy of the snout and jaws (Cox-Fernandes, 1998).
Amongst these are the hypermorphic growth of the
snout in males of some species of Apteronotus (Cox-
Fernandes, Lundberg & Riginos, 2002; Albert &
Crampton, 2009) and the elaboration of the anterior
portion of the jaws and dentition in Sternarchogiton
(de Santana & Crampton, 2007). Many species of
Sternarchorhynchus are characterized by secondary
sexual dimorphism of multiple body systems. Non-
cephalic sexually dimorphic features of some species
of Sternarchorhynchus involve pigmentation and
more often the location of the anus and urogenital
pore. More dramatic are the sexually dimorphic
attributes involving the snout and jaws. Mature
males of Sternarchorhynchus mormyrus have a wider
snout than conspecific females of comparable body
sizes, whereas the distinct fleshy dorsomedian ridge
on the snout is limited to the males of Sternarcho-
rhynchus kokraimoro. Some species in the genus dem-
onstrate sexually dimorphic differences in the degree
of curvature of the elongate snout. Most striking of
the sexually dimorphic features in Sternarchorhyn-
chus are the lengthened and transversely widened
anterior portions of the dentaries in some larger
males of ten species. This expanded region is rounded
in the transverse plane and dorsally forms a bulbous
structure crowned with a patch of variably enlarged
teeth. Such enlarged dentition may be brought into
play by males in confrontations during breeding con-
tests (Marrero & Taphorn, 1991; Kirschbaum, 1995;
Cox-Fernandes et al., 2002). Although these elabora-
tions of the lower jaw and associated dentition occur
only in mature males, they are absent in some con-
specific males of comparable body sizes with well-
developed testes. Presence versus absence of these
modifications potentially reflects a social hierarchy
wherein the jaw and dentition elaborations are
limited to alpha males. Alternatively, variability in
the expression of these features may reflect season-
ality in the manifestation of the modifications of the
lower jaw and associated dentition.
As in other gymnotiforms, the species of Sternar-
chorhynchus generate and receive weak electrical
signals that function in electrocommunication and
electrolocation. Electrocommunication serves to
signal species identity and aspects of behaviour,
whereas electrolocation permits the detection of
organisms and objects in the surrounding aquatic
system via distortions of the electric field generated
by the individual [see Carr & Maler, 1986 and Albert
& Crampton (2005) for discussions of the adaptations
associated with these functions]. Members of Sterna-
rchorhynchus generate at least four types of electric
organ discharges (EODs). These periodic (wave-type)
signals are interspecifically variable with discharges
ranging between 944 and 1922 Hz and considerable
overlap in distance ranges between congeners
(Crampton & Albert, 2006: 688?689, figs 23.10?11).
Some Sternarchorhynchus species have a unique
EOD modulation pattern (active phase coupling) pos-
sibly associated with information exchange between
potential mates (Langner & Scheich, 1978;
Gottschalk & Scheich, 1979); however, the degree to
which these unusual EOD patterns are universal
across the genus is unknown.
Species of Sternarchorhynchus dwell in diverse
habitats, with many members of the genus resident in
the deep-water benthos of the larger rivers. In these
habitats, the species of Sternarchorhynchus consti-
tute a significant portion of the fish biomass (Lopez-
Rojas, Lundberg & Marsh, 1984; Lundberg et al.,
1987; Marrero & Taphorn, 1991). Jointly with other
deep-water species of the Apteronotidae, they are
preyed upon extensively by several catfish species of
large body sizes (Marrero & Taphorn, 1991; Barbarino
Duque & Winemiller, 2003). Some species of Sterna-
rchorhynchus are adapted for life in smaller rivers
and tributary streams where they often inhabit high-
energy settings such as rapids and/or pools at the
base of waterfalls (e.g. Sternarchorhynchus severii,
Sternarchorhynchus caboclo; de Santana & Nogueira,
2006: 90).
Impoundments across the range of Sternarchorhyn-
chus drowned many of the rapids and waterfalls that
are preferred habitats for many species of the genus
(Ferreira, 1995: 34?35; Campos-da-Paz, 2005: 399).
224 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Proposed development projects furthermore threaten
other sites occupied or likely to be occupied by
members of the genus. Habitat loss of this scale
renders species of Sternarchorhynchus vulnerable to
extinction at least at the local level (e.g. Sternarcho-
rhynchus britskii in the upper Rio Paran?; Campos-
da-Paz, 2005: 399; Triques, 2007: 125). Indeed, some
species described as new herein are possibly either
extinct or face imminent extinction.
Deep main river channels, rapids, pools at the
bases of waterfalls and large rapids, and subterra-
nean waters potentially inhabited by species of Ster-
narchorhynchus (Campos-da-Paz, 2000; Bichuette &
Trajano, 2003) remain unsampled ichthyologically in
many regions. When surveyed, the ichthyofauna in
these difficult-to-collect habitats is nearly always
incompletely sampled because of resource limitations
and/or restrictions on the use of the collecting
methods (e.g. rotenone) often prerequisite for exhaus-
tive collections of such faunas. Consequently, nearly
all species of Sternarchorhynchus described to date
are based on one to relatively few specimens. One
notable exception (Sternarchorhynchus roseni) was
described from a locality that was the subject of
long-term sampling efforts. Limited samples of many
species of Sternarchorhynchus continue to bedevil
systematic, ecological, and behavioural studies of the
genus; problems typified by the restricted samples of
some of the species described herein. Rectifying the
problem of limited sample size is unlikely in the short
term, if ever, because of resource limitations; a
problem compounded by the accelerating anthropo-
genic modifications of many of the habitats occupied
by species of Sternarchorhynchus.
M?ller & Troschel (1848) described the first species
now placed in Sternarchorhynchus as Sternarchus
oxyrhynchus. The next three decades saw the pro-
posal of Sternarchorhynchus by Castelnau (1855), the
description of S. mormyrus by Steindachner (1868a),
the proposal of the subgenus Rhamphosternarchus
within Sternarchus by G?nther (1870) for species now
assigned to Sternarchorhynchus, and the description
of Sternarchorhynchus curvirostris by Boulenger
(1887). In a dramatic reversal of the practice of pro-
gressive description of additional species, Ellis (1913)
placed S. mormyrus and S. curvirostris as junior
synonyms of Sternarchorhynchus oxyrhynchus and
recognized a monotypic Sternarchorhynchus. Ellis?
concept of S. oxyrhynchus was of a geographically
broadly distributed species characterized by pro-
nounced variation in external head morphology and
anal-fin ray counts.
This broadly inclusive S. oxyrhynchus held sway for
over a half a century (e.g. Eigenmann & Allen, 1942:
318; Fowler, 1951: 431) until Fern?ndez-Y?pez (1967)
resurrected S. curvirostris and S. mormyrus from the
synonymy of S. oxyrhynchus based on differences
between what he identified as samples of those
nominal forms. Fern?ndez-Y?pez failed to specify the
localities where his samples originated, but the illus-
trations in that publication make it clear that the
material considered S. curvirostris was misidentified
and that the purported specimens of S. mormyrus
were probably another species. Notwithstanding
these misidentifications, Fern?ndez-Y?pez correctly
surmised that Sternarchorhynchus encompassed
more than one species. Subsequent authors followed
Fern?ndez-Y?pez and recognized S. oxyrhynchus, S.
mormyrus, and S. curvirostris.
The century-plus hiatus in the description of
nominal species of Sternarchorhynchus ended with
Mago-Leccia?s (1994) description of S. roseni from the
R?o Orinoco system. Soon thereafter, Campos-da-Paz
(2000) summarized the state of knowledge of the
taxonomy of Sternarchorhynchus, addressed the ques-
tions of the monophyly of, and intrarelationships
within, the genus, and described two new species
(S. britskii, Sternarchorhynchus mesensis). de
Santana & Taphorn (2006; Sternarchorhynchus
gnomus), de Santana & Crampton (2006; Sternarcho-
rhynchus curumim), and de Santana & Nogueira
(2006; S. severii, S. caboclo) described four additional
species of Sternarchorhynchus.
Notwithstanding the recent flurry of species
descriptions, Albert & Crampton (2005) and de
Santana & Nogueira (2006) proposed that thorough
analyses of Sternarchorhynchus across its range
would reveal additional undescribed species. Results
reported on herein confirm those predications; indeed
those forecasts as to the number of undescribed
species proved quite conservative. In addition to
the ten previously recognized Sternarchorhynchus
species, we describe 22 new species of the genus.
Populations of Sternarchorhynchus that probably rep-
resent additional yet-to-be described species are iden-
tified, but formal descriptions of those forms deferred
for various reasons. Nonetheless, the 32 species of
Sternarchorhynchus account for 40% of the species in
the Apteronotidae, the ghost electric knifefishes (de
Santana, Castillo & Taphorn, 2006; this study).
Campos-da-Paz (2000) and Albert (2001) delved
into the question of the relationships of and within
Sternarchorhynchus and proposed Platyurosternar-
chus as a potential sister group to that genus. Those
analyses encompassed solely the limited number of
species then recognized within the genus. The numer-
ous species described as new in Sternarchorhynchus
since the phylogenetic analysis by Campos-da-Paz
(2000), along with the continued description of phy-
logenetically informative characters within the Gym-
notiformes, necessitate a re-evaluation of the
evidence for the monophyly of the genus. More impor-
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 225
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
tantly it is appropriate to develop an intrageneric
phylogenetic hypothesis incorporating the dramati-
cally higher number of species now recognized within
Sternarchorhynchus.
This study had four primary goals:
1. To evaluate the hypothesis of the monophyly of
Sternarchorhynchus and its sister-group relation-
ship with Platyurosternarchus;
2. To generate a hypothesis of the phylogenetic rela-
tionships within Sternarchorhynchus;
3. To examine the correlations amongst major shifts
in the jaws and associated structures, major tran-
sitions in body sizes, and shifts in habitat prefer-
ences in the species of Sternarchorhynchus within
the context of the reconstructed phylogeny; and
4. To provide a comprehensive revision of species of
Sternarchorhynchus with associated keys, species
accounts, and distribution maps.
MATERIAL AND METHODS
Hypotheses of phylogenetic relationships are based on
cladistic methods first proposed by Hennig (1966) and
subsequently elaborated by a series of authors (e.g.
Nelson & Platnick, 1981; Wiley, 1981; Wiley et al.,
1991; Forey et al., 1996). The method used in the
search for the hypothesis best supported by the incor-
porated data was Wagner parsimony under which
reversals of, and convergencies in, characters are
permissible and quantified equally (Swofford & Mad-
dison, 1987). The analysis was carried out using
PAUP*4.0B10 (Swofford, 2003). A parallel analysis
was undertaken in NONA (Goloboff, 1999) in its shell
WINCLADA (Nixon, 1999?2002). The matrix of 88
characters and 34 terminal taxa was built in
MacClade (Maddison & Maddison, 2005) with tree
manipulations and character diagnoses generated
through the same program. Characters were coded as
unordered in the analysis of the data matrix. Outgroup
comparisons served as the basis for polarity inferences
of character. Rooting was a posteriori at the clade
formed by Orthosternarchus and Sternarchorham-
phus, which is hypothesized as a basal group in the
Apteronotidae (Albert, 2001; Triques, 2005; Hilton
et al., 2007). Ambiguous character distributions were
resolved using the accelerated transformation optimi-
zation [ACCTRAN (Farris optimization)], which maxi-
mizes reversals over parallelism (de Pinna, 1991).
Delayed transformation optimization (DELTRAN)
optimizations are also discussed in Appendix 2.
MERISTICS AND MORPHOMETRICS
Many specimens of gymnotiforms suffer damage to or
loss of their tails, most likely from predation, in some
instances by other knifefishes (Lundberg et al., 1996:
666). Caudal region damage is often followed by a
partial regeneration, with most so-damaged individu-
als recognizable by the clearly ?truncated, or abruptly
narrowed and/or abruptly depigmented tails.? (Mago-
Leccia, Lundberg & Baskin, 1985: 1); however, some
damaged individuals lack these external indictors. We
excluded specimens with apparently regenerated pos-
terior regions of the body from counts of anal- and
caudal-fin rays and from morphometrics involving
total length, tail length, and tail depth.
Counts
Vertebral counts were obtained from radiographs and
cleared and stained specimens. The Weberian appa-
ratus in gymnotiforms incorporates the four anterior-
most centra with the second and third elements very
closely applied, or sometimes fused, to each other, but
still apparent (Hopkins, 1991: 152; Campos-da-Paz,
2000: 524). Abdominal vertebrae are the anterior com-
ponents of the series that bear a pair of ribs extending
over and along the sides of the abdominal cavity and
include the vertebrae of the Weberian complex. Tran-
sitional vertebrae lack both ribs and neural spines.
Counts of anal-, pectoral-, and caudal-fin rays were
most often taken under a microscope using transmit-
ted light with those data supplemented by counts
taken from digital radiographs. In the count of the
pectoral-fin rays, unbranched anterior rays are repre-
sented by lower case Roman numerals and branched
rays by Arabic numbers. The count of branched rays
includes all rays posterior to the anterior unbranched
rays including the posteriormost ray in the series that
is apparently sometimes unbranched. Anal-fin ray
counts are presented in terms of anterior unbranched
and total rays. Caudal-fin rays are the total number of
those rays. Observations on the number and form of
the branchiostegal rays are from cleared and stained
specimens and radiographs.
Measurements
Morphological measurements are point-to-point dis-
tances utilizing digital callipers to 0.1 mm total
length (TL) with data for each species presented in
tabular form in each species account. Measurements
were as follows: anal-fin base ? the distance between
the bases of the first and last rays of the anal fin;
anus to anal-fin insertion ? the distance from the
posterior margin of the anus to the base of the first
anal-fin ray; branchial opening ? the height of the
opening measured along the vertical; caudal length ?
the distance from the base of the posteriormost ray of
the anal fin to the posteriormost point on the body;
caudal-fin length ? the distance from the hypural
joint to the distalmost point along the posterior
margin of the caudal fin; eye diameter ? the horizon-
tal width of the eye; greatest body depth ? the great-
226 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
est vertical extent of the body, usually situated
slightly anterior to the dorsal-fin origin; head depth
at eye ? the head depth measured at the eye; head
depth at nape ? the head depth measured at the nape;
head width ? the head width measured at the oper-
cular region; head length ? the distance from the tip
of the snout to the posterodorsal angle of the bran-
chial opening; internarial distance ? the distance
between the posterior of the base of the tubular
anterior naris and the anterior margin of the opening
of the posterior naris; interocular width (interorbital
width of some previous authors) ? the minimum
width between the dorsal margins of the orbits;
length to end of anal-fin (the LEA of Mago-Leccia
et al., 1985) ? the distance from the tip of the snout to
the end of the base of the anal fin; mouth length ? the
distance from the tip of the snout to the rictus of the
mouth; pectoral-fin length ? the distance between the
base of the dorsalmost ray of the pectoral fin and the
distalmost point on the margin of the fin; posterior
naris to snout ? the distance from the anterior border
of the naris to the tip of snout; posterior naris to eye
? the distance from the posterior border of the naris
to the anterior margin of the eye; postocular distance
? the distance from the posterior margin of the eye to
the posterodorsal angle of the branchial opening;
preanal-fin distance ? the distance from the tip of the
snout to the base of the first anal-fin ray; prepectoral-
fin distance ? the distance from the tip of the snout to
the base of the dorsalmost pectoral-fin ray; snout
length ? the distance from the tip of the snout to the
anterior margin of the eye; snout to anus ? the
distance from the tip of the snout to the anterior
margin of the anus; tail depth ? the depth of the tail
measured immediately posterior of the base of the
last anal-fin ray; and total length ? distance from the
tip of the snout to the end of the tip of the caudal fin.
Whenever possible, the sex of specimens was
assessed via dissections in order to evaluate possible
secondary sexual dimorphism. Ovaries of mature
females are packed with yellow or cream-coloured
eggs. Testes in mature males are, in contrast, white
and smooth.
ABBREVIATIONS
Abbreviations used in text are: CS, cleared and
stained; HL, head length; LEA, length from tip of
snout to end of anal fin; and TL, total length.
Abbreviations for institutions and collections are:
AMNH, American Museum of Natural History, New
York; ANSP, Academy of Natural Sciences of Phila-
delphia; AUM, Auburn University Museum, Auburn;
BMNH, The Natural History Museum, London [for-
merly British Museum (Natural History)]; CAS, Cali-
fornia Academy of Sciences, San Francisco; CAS-SU,
former Stanford University collections, now deposited
in CAS; CM, Carnegie Museum, Pittsburg, fish col-
lections now deposited at various depositories; CU,
Cornell University, Ithaca; FMNH, Field Museum of
Natural History, Chicago; IAVHP, Instituto Alexander
von Humboldt, Colleci?n de Peces, Villa de Leyva,
Colombia; INHS, Illinois Natural History Survey,
Champaign; INPA, Instituto Nacional de Pesquisas
da Amaz?nia, Manaus; IRScNB, Institute Royal de
Sciences Naturelles de Belgique, Brussels; IDSM,
Instituto de Desenvolvimento Sustenavel, Mamiraua,
Tef?, Brazil; IU, Indiana University, Bloomington, fish
collections now at various depositories; LACM, Los
Angeles County Museum, Los Angeles; MBUCV,
Museo de Biolog?a de la Universidad Central de
Venezuela, Caracas; MCNG, Museum de Ciencias
Naturales, Guanare; MCP, Museu de Ci?ncias e Tec-
nologia, Pontificia Universidade Cat?lica do Rio
Grande de Sul, Porto Alegre; MCZ, Museum of Com-
parative Zoology, Harvard University, Cambridge;
MNRJ, Museu National, Rio de Janeiro; MUSM,
Museo de Historia Natural de la Universidad Nacio-
nal Mayor de San Marcos, Lima; MZUSP, Museu de
Zoologia da Universidade de S?o Paulo; NMW,
Naturhistorisches Museum Wien, Vienna; ROM,
Royal Ontario Museum, Toronto; UF, Florida Museum
of Natural History, Gainesville; UMMZ, Museum of
Zoology, University of Michigan, Ann Arbor; USNM,
National Museum of Natural History, Smithsonian
Institution, Washington; ZMA, Zoologisch Museum,
Amsterdam; and ZMB, Museum f?r Naturkunde der
Humboldt Universit?t, Zoologisches Museum, Berlin.
LOCALITY DATA
Material examined for each species is geographically
sorted by country and then, when available, major
political divisions within countries, followed by spe-
cific localities within those divisions with the locali-
ties grouped to the degree possible by proximity. In
the case of new species, the locality information is
supplemented by data on collectors and date collected.
Locality information (and collectors where appropri-
ate) is followed by institutional abbreviation, cata-
logue number, and number of specimens in lot.
Parenthetical information includes the range of total
lengths of the specimens and when appropriate infor-
mation about type status (for previously described
species), type of preparation if not whole alcohol
specimens, the sex of the specimens when determin-
able, and other pertinent information.
NOMENCLATURE
Family level names for outgroups are those utilized in
Checklist of the Freshwater Fishes of South and
Central America [CLOFFSCA (Reis, Kullander & Fer-
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 227
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
raris, 2003)]. The narrow, posteriorly tapering, fleshy
structure that arises from the mid-dorsal line of the
posterior half of the body and runs along and is
attached to the mid-dorsal groove on the body is
termed the electroreceptive filament. This structure
was equated with the adipose fin by Ellis (1913) and
termed the dorsal thong by Mago-Leccia (1994). The
homology of this structure remains uncertain but as
indicated by the name it serves an electroreceptive
function (see discussion by Franchina & Hopkins,
1996).
Osteological terminology is that of Weitzman (1962)
with the following modifications. The use of epioccipi-
tal rather than epiotic corresponds to the practice
proposed by Patterson (1975). Following Nelson
(1969), the ossification traditionally termed the
epihyal is referred to as the posterior ceratohyal, and
the ceratohyal of many previous authors as the ante-
rior ceratohyal. The ethmoid of Weitzman (1962) is
termed the mesethmoid following Fink & Fink (1981,
1996). Vomer is used instead of prevomer, but with
the vomer considered to be fused to the ventral
ethmoid as is the case in various groups of fishes
(Johnson & Patterson, 1996). The anterior portion of
that combined bone is identified as the ventral
ethmoid as is the practice in recent analyses involving
gymnotiforms (Albert, 2001; Hilton et al., 2007).
Intercalar is used instead of opisthotic as per the
practice in recent studies (Albert, 2001). Following
recent authors publishing on gymnotiforms we utilize
endopterygoid rather than mesopterygoid (Fink &
Fink, 1996). Recent literature on gymnotiform phy-
logeny includes alternative numbering systems for
the gill arches (e.g., Albert, 2001). We follow Hilton
et al. (2007) in using the number system for gill
arches typical for studies of actinopterygian fishes.
Nomenclature for muscles and associated tendons is
that of Winterbottom (1974).
OSTEOLOGICAL PREPARATIONS
Samples were cleared and counterstained (CS) for
cartilage and bone using the method outlined by Taylor
& Van Dyke (1985). Removal of the pectoral girdle,
suspensorium, and components of the head followed
procedures outlined by Weitzman (1974). In order to
identify anomalous features, two or more individuals
of each species were prepared when specimens were of
appropriate size and samples sufficiently large. The
osteology of 23 of the 32 species of Sternarchorhynchus
was examined via cleared and stained specimens.
Cleared and counterstained specimens of these species
are listed in Supporting Information Appendix S1.
Specimens of Sternarchorhynchus axelrodi, Sternar-
chorhynchus freemani, Sternarchorhynchus galibi,
Sternarchorhynchus kokraimoro, Sternarchorhynchus
marreroi, Sternarchorhynchus taphorni, Sternarcho-
rhynchus yepezi, and Sternarchorhynchus villasboasi
could not be prepared in that fashion because of small
sample sizes or because available specimens were of
large body sizes. Radiographs served as supplemen-
tary sources of data for these species.
Available specimens of S. axelrodi are too large to
clear and stain, but we were able to code the species
for many osteological characters via radiographs of
the type series (see Material examined under species
account). That information and the external features
allowed us to code the species for 73 of the 88 char-
acters in the matrix. The question of missing data is
problematic in phylogenetic analyses and has been
discussed in various contexts (Novaceck, 1992; Wiens,
2003, 2005 and references therein). Wiens (2003,
2005) pointed out that even in instances of incomplete
data, the available information will be phylogeneti-
cally informative when sufficient characters are
coded. That has proved to be the case in this study,
with the hypothesis of the phylogenetic relationships
of S. axelrodi well supported.
FRAMEWORK FOR OUTGROUP COMPARISONS
The phylogenetic analysis centres on relationships
within Sternarchorhynchus rather than suprageneric
relationships in the Apteronotidae, a problem that
Hilton et al. (2007) concluded is ?still the subject of
debate? and whose resolution extends beyond the
scope of this project. For the purposes of the phylo-
genetic analysis herein, we focus on Platyurosternar-
chus as the sister group to Sternarchorhynchus
according to results of the more encompassing phylo-
genetic hypothesis based on multiple character
systems examined herein and in some previous analy-
ses [Albert & Campos-da-Paz (1998: 429, fig. 2 ? clade
H), Campos-da-Paz (2000: 527 ? clade C), Albert
(2001: 72, fig. 43 ? clade V)].
The question of the appropriate second outgroup to
Sternarchorhynchus is less straightforward. Campos-
da-Paz (1995) identified a series of similarities
between Orthosternarchus tamandua and Sternar-
chorhamphus muelleri, a relationship reiterated by
Alves-Gomes et al. (1995) based on genetic, morpho-
logic and electrophysiologic data. Albert (2001), in
turn, proposed that O. tamandua plus Sternar-
chorhamphus muelleri formed the sister group to the
clade formed by Platyurosternarchus plus Sternarcho-
rhynchus (Albert, 2001: 72, fig. 43 ? clades U and V,
respectively). Subsequent authors (Triques, 2005;
Hilton et al., 2007) advanced additional evidence for
the monophyly of the clade formed by O. tamandua
and Sternarchorhamphus muelleri based on morpho-
logical data, but questioned the placement of the
lineage formed by those two species as the sister
228 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
group to the clade formed by Platyurosternarchus
plus Sternarchorhynchus. In particular, Hilton et al.
(2007) highlighted problematic homology assumptions
underpinning that phylogenetic hypothesis (see com-
ments under Convergence in elongation of snout in
Discussion). That issue notwithstanding, Hilton
et al. noted that all four genera (Orthosternarchus,
Platyurosternarchus, Sternarchorhamphus, and Ster-
narchorhynchus) were relatively basal to ?other apter-
onotid taxa.? A lack of resolution in the phylogenetic
scheme proposed by Triques (2005) renders it unin-
formative on this issue, but the pattern of relation-
ships does not run counter to that proposal. As such
the Orthosternarchus-Sternarchorhamphus clade
serves as an appropriate secondary outgroup to Ster-
narchorhynchus for the purposes of our analysis.
Concepts of relationships within the rest of the
Apteronotidae remain incompletely resolved (Cramp-
ton & Albert, 2006: fig. 23.11). Representative taxa
from the remaining major clades across the rest of the
Apteronotidae (Albert, 2001) were included as more
distant outgroups for the purposes of the phylogenetic
analysis (Apteronotus cuchillo, Apteronotus rostratus,
Apteronotus albifrons, ?Apteronotus? apurensis, Ster-
narchella orthos, and Sternarchogiton labiatus).
?Apteronotus? apurensis is a member of a small clade
that Albert & Campos-da-Paz (1998) hypothesized
failed to form a monophyletic group with Apteronotus
sensu stricto. These authors used the convention of
?Apteronotus? to highlight the uncertainty concerning
the appropriate generic assignment for ?A.? apurensis
and the three other species in that clade.
Phylogenetic position of Ubidia
Divergent placements of the monotypic genus
Ubidia necessitate comment. Triques (2005) con-
cluded that Platyurosternarchus was the sister clade
to Ubidia magdalenensis. Under the hypothesis
advanced by that author, the Platyurosternarchus?
Ubidia clade formed the sister group to Sternarcho-
rhynchus. A sister-group relationship between
Ubidia and Platyurosternarchus was supported by
one proposed synapomorphy ? ?the marmorated pig-
mentation pattern of the body with large dark
blotches formed of dense aggregations of chromato-
phores? (Triques, 2005: 142; our translation). Marm-
oration was alternatively cited by Albert (2001) as
synapomorphic for the members of the Apteronotus
magdalenensis group [A. magdalenensis (= Ubidia
magdalenensis) and A. cuchillo], which share several
other hypothesized synapomorphies. In that analysis
these species were deeply embedded within Apter-
onotus, with that genus separated from Platyuroster-
narchus and Sternarchorhynchus by several nodes
supported by a series of characters (Albert, 2001:
fig. 43). Both coding and homology questions pertain
to the preferability of one of these alternative
hypotheses as to the relationships of Ubidia with
Apteronotus versus Platyurosternarchus.
Triques (2005) coded A. cuchillo as lacking marm-
oration. Examination of the types of A. cuchillo
revealed marmoration formed of small scale, irregu-
lar, dark and light patterning over the entire head
and body other than for the lightly coloured mid-
dorsal region. Comparable patterning occurs in U.
magdalenensis, albeit with the contrast between light
and dark regions somewhat muted. Similar marmora-
tion also occurs in the more recently described Apter-
onotus eschmeyeri (de Santana & Maldonado-Ocampo,
2005: fig. 5a).
One could broadly characterize the coloration of
Platyurosternarchus as marmorated; however, the
pigmentation scheme of that genus differs notably
from that of A. cuchillo, A. eschmeyeri, and U.
magdalenensis and was characterized by Mago-
Leccia (1994) as ?highly diagnostic? within the Gym-
notiformes. The species of Platyurosternarchus have
intense dark pigmentation on the ventral portions of
the body with the darker patches in that region
nearly contiguous and interrupted by some expan-
sive more lightly pigmented regions (Ferreira et al.,
2007: 164; de Santana & Vari, 2009: figs 1, 5). This
pattern of expansive dark versus light pigmentation
patches differs dramatically from the finer marm-
oration characteristic of A. cuchillo, A. eschmeyeri,
and U. magdalenensis. Platyurosternarchus has
more lightly coloured dorsolateral and dorsal regions
of the body with some irregular large patches of
somewhat darker pigmentation within the ground
coloration; again a pattern absent in A. cuchillo, A.
eschmeyeri, and U. magdalenensis. In light of these
differences, we judge the marmoration in A.
cuchillo, A. eschmeyeri, and U. magdalenensis as
nonhomologous with the pigmentation pattern of
Platyurosternarchus. This nonhomology eliminates
support for the Ubidia?Platyurosternarchus clade
proposed by Triques (2005) with those two genera
plus Sternarchorhynchus thereby forming a tri-
chotomy under that scheme of relationships. This,
nonetheless, leaves Ubidia as potentially closely
related to Sternarchorhynchus.
As noted, Albert (2001: fig. 43) proposed that a
series of characters support the hypothesis that the
relationships of Ubidia lie with a component of
Apteronotus rather than Platyurosternarchus and
Sternarchorhynchus. Apteronotus cuchillo and U.
magdalenensis share distinctive juvenile coloration
patterns, most notably lightly coloured bands proxi-
mate to the rear of the anal fin and the base of the
caudal fin. These bands encircle the body within the
dark background coloration (Schultz, 1949: 71, pl. 3,
fig. A). Comparable ontogenetically vanishing con-
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 229
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
trasting coloration characterizes various Apteronotus
species including A. eschmeyeri (de Santana et al.,
2004). Neither species of Platyurosternarchus demon-
strates a comparable pigmentation pattern. The
common possession of this distinctive pigmentation
pattern provides further support for the hypothesis
that the relationships of U. magdalenensis lie with a
component of the genus Apteronotus.
Coding of internal features of U. magdalenensis by
Albert (2001) and Triques (2005) apparently was
limited to characters shown in the partial illustra-
tions of head osteology in the original description by
Miles (1945: fig. 11). This impediment resulted in
numerous uncoded characters and was encumbered
by apparent errors in those illustrations. Of note is
the lateral ethmoid which, although present in speci-
mens of Ubidia examined in this study, was absent
from the illustration with its absence versus presence
coded as unknown by Triques (2005). A lateral
ethmoid is always present in the species of Apterono-
tus contrary to the derived absence of that element
in Platyurosternarchus and Sternarchorhynchus.
Triques (2005) proposed other features uniting Ubidia
to Platyurosternarchus plus Sternarchorhynchus. Two
of the characters optimized at that clade rather than
being universal for the three genera. Comments on
the other proposed synapomorphies are provided
under the discussion of the features in the analysis
(characters 2, 23, 26, 68, 87) and ?Convergence in the
elongation of the snout?. The evidence from coloration
and the lateral ethmoid, complemented by the infor-
mation presented by Albert (2001: 76, 77, fig. 43, see
synapomorphies for nodes Z, AA, AB, AC), support the
hypothesis that the relationships of Ubidia lie with a
subunit of Apteronotus rather than with Platyuroster-
narchus and Sternarchorhynchus. Ubidia is conse-
quently not included as a proximate outgroup to
Sternarchorhynchus in the phylogenetic analysis.
PHYLOGENETIC RESULTS
Eighty-eight characters that vary within Platyuro-
sternarchus and Sternarchorhynchus, diagnose one of
those genera as monophyletic, or are informative for
resolution of structure in the outgroup phylogeny
were examined in the cleared and stained specimens
(Supporting Information Appendix S1) and whole
specimens listed under the taxonomic accounts. Char-
acters were divided into two or more discrete charac-
ter states, with multistate characters present for
three characters. Characters were coded as unordered
in the analysis of the data matrix (Appendix 1). A
heuristic search with stepwise addition, simple addi-
tional sequence, branch-swapping tree bisection?
reconnection, and ?max? trees saved in PAUP* 4.0b10
(Swofford, 2003) included all outgroups with branches
of zero maximum length collapsed and yielded eight
most parsimonious trees each with a length of 190,
consistency index (CI) = 0.484, and retention index
(RI) = 0.820. The analysis using minimum tree length
of zero resulted in four trees of the same topology and
scores. A parallel analysis in NONA (Goloboff, 1999)
in its shell WINCLADA (Nixon, 1999?2002) using the
same conditions as in PAUP* and a search strategy of
Mult* yielded four trees with the same topology as in
the PAUP* analysis with a length of 190, CI = 0.480,
and RI = 0.810. The strict consensus tree generated in
both of the two software packages was identical, with
a length of 193, CI = 0.477, and RI = 0.814 and is
presented in Figure 23. Only two of these trees were
pertinent to alternative hypotheses of relationships
within the lineage formed by Platyurosternarchus and
Sternarchorhynchus and involved the highly imbed-
ded clade 24 within the latter genus (Fig. 24). The
other alternative trees pertain to differing patterns of
relationships amongst more distant outgroup taxa
and as such are not germane to the foci of this study.
CHARACTER DESCRIPTION AND ANALYSIS
The following discussion is arranged by discrete body
systems ordered in an approximately anterior to pos-
terior sequence. Characters involving multiple por-
tions of an individual (e.g. coloration) are last. The
description of each of the characters first includes a
brief descriptor of the character followed by summa-
ries of the alternative character states, the consis-
tency and retention indices under the final
phylogenetic hypothesis (Fig. 23), and finally a dis-
cussion of the distribution of character states
amongst the examined species and members of the
examined outgroups. Additional comments on the
characters follow where appropriate.
MOUTH
1. Extent of gape: (0) posterior terminus of gape not
extending posteriorly to beyond vertical through pos-
terior nares; (1) posterior terminus of gape extending
posteriorly to beyond vertical through posterior nares
(CI = 1.000; RI = 1.000).
Members of the proximate outgroups (Orthosterna-
rchus, Sternarchorhamphus), along with Sternarch-
ella orthos and all species of Sternarchorhynchus with
the exception of S. goeldii and S. oxyrhynchus, have
notably short mouths with the posterior limit of the
gape falling short of the vertical through the posterior
nares (state 0; Fig. 1B). Although the mouths in S.
goeldii and S. oxyrhynchus are quite short along the
snout axis compared to those in most fishes including
many gymnotiforms (e.g. Magosternarchus, Lundberg
et al., 1996: fig. 2) they are, nonetheless, distinctly
230 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
longer than the form of the mouth present in all
remaining species of Sternarchorhynchus. As a
consequence, the gape in S. goeldii and S. oxyrhyn-
chus extends posteriorly distinctly beyond the vertical
running through the posterior nares (state 1; Fig. 1A)
rather than terminating short of that landmark. This
character could not be coded for the species of
Platyurosternarchus or the outgroups other than
Orthosternarchus, Sternarchorhamphus, and Sterna-
rchella orthos. In those taxa the proportionally dis-
tinctly posterior location of the nares relative to the
location of the apertures in Orthosternarchus
tamandua, Sternarchorhamphus muelleri, and the
species of Sternarchorhynchus means that that those
openings cannot serve as homologous landmarks,
thereby rendering coding impossible.
2. Presence or absence of small fold of skin on
anterolateral surface of upper lip: (0) skin of upper lip
flat and without fold; (1) skin of upper lip with dis-
tinct fold (CI = 0.500; RI = 0.900).
Variation in the morphology of the skin overlying
the anterolateral surface of the upper lip was
reported by Triques (2005: 26) for apteronotids.
Triques (2005) reported the fold as present in S.
oxyrhynchus. His material originated in the Amazon
basin, a region outside the known range of the species
and is likely to represent another species. Our analy-
sis found that the upper lip lacks a skin fold in the
species of Orthosternarchus, Platyurosternarchus, and
Sternarchorhamphus. Within Sternarchorhynchus the
fold is similarly absent in S. goeldii and S. oxyrhyn-
chus (Fig. 1A). Both of those species of Sternarcho-
rhynchus also share a mouth form unique in the
genus (see character 1). All other species of Sternar-
chorhynchus have a distinct fold within the skin of
the upper lip (Fig. 1B) with that feature also present
in Sternarchella orthos amongst the more distant
outgroups.
UPPER JAW
3. Form of premaxilla: (0) somewhat to distinctly
elongate from ventral view; (1) compact with longitu-
dinal length approximately equal to transverse width
(CI = 0.500; RI = 0.857).
As would be expected given the diversity of head
forms across the Apteronotidae, the members of the
family also demonstrate variation in the form of the
premaxilla. In Platyurosternarchus crypticus and
Platyurosternarchus macrostoma the premaxilla is
Figure 1. Lateral view of anterior portion of snout of A, Sternarchorhynchus oxyrhynchus, ANSP 162670; and B,
Sternarchorhynchus caboclo, INPA 10594, showing differing degree of development of mouth and fold of skin at rear of
rictus.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 231
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
anteroposteriorly variably elongate, a condition found
in the other proximate outgroups to Sternarchorhyn-
chus (Sternarchorhamphus muelleri, Campos-da-Paz,
1995: fig. 4; Orthosternarchus tamandua, Hilton
et al., 2007: fig. 10) and various more distantly related
gymnotiforms (Albert, 2001: fig. 6). An anteroposteri-
orly elongate premaxilla similarly characterizes a
minority of the species of Sternarchorhynchus (S.
axelrodi, S. goeldii, S. mormyrus, and S. oxyrhynchus;
Fig. 2). The remaining species of Sternarchorhynchus
have a compact form of the premaxilla in which the
longitudinal length of the bone approximately equals
its transverse width (Fig. 3). Looking beyond the
immediate outgroups to Sternarchorhynchus, we find
that comparable compact premaxillae are also
present amongst examined apteronotids in the
species of Apteronotus included in this study along
with Sternarchella orthos (Lundberg et al., 1996:
fig. 4c) and Sternarchogiton labiatus.
4. Presence or absence of teeth on premaxilla: (0)
teeth absent; (1) teeth present (CI = 0.500;
RI = 0.500).
Presence of premaxillary teeth is the common con-
dition across the Gymnotiformes. The species of
Orthosternarchus (Hilton et al., 2007: fig. 12), Sterna-
rchorhynchus (Figs 2, 3), and Sternarchorhamphus
(Campos-da-Paz, 1995: fig. 4) have premaxillary teeth
present, albeit with the form of the dentition on the
bone varying amongst those taxa. Premaxillary den-
tition is, in contrast, lacking in P. crypticus and P.
macrostoma. Amongst the more distant outgroups
included in the analysis, an edentulous premaxilla
similarly occurs in Sternarchogiton labiatus. Other
apteronotids not included in the outgroups that
without premaxillary dentition are Apteronotus
cuchillejo and the species of Adontosternarchus.
5. Degree of development of anterior portion of
maxilla: (0) with distinct anteriorly pointed process;
(1) without distinct anterior process (CI = 1.000;
RI = 1.000).
Immediate outgroups to Sternarchorhynchus
[Orthosternarchus tamandua (Hilton et al., 2007:
fig. 12), P. crypticus, P. macrostoma, Sternarchorham-
phus muelleri (Campos-da-Paz, 1995: fig. 4)] have a
distinct, somewhat to distinctly anteriorly pointed
process of the maxilla from lateral view (state 0).
That condition is also present in the more distant
outgroup genera Apteronotus, Sternarchella, and
Figure 2. Premaxilla and anterior portion of neurocranium of Sternarchorhynchus goeldii, MCZ 46887; dorsal view,
anterior to left.
Figure 3. Premaxilla and anterior portion of neurocranium of Sternarchorhynchus roseni, MCNG 52591; dorsal view,
anterior to left.
232 C. D. DE SANTANA and R. P. VARI
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Sternarchogiton. All species of Sternarchorhynchus
alternatively have an anterior portion of the maxilla
that lacks an anterior extension and have instead a
rounded to square margin to that portion of the bone
(state 1; Fig. 4).
6. Form of anterior portion of maxilla: (0) moder-
ately expanded; (1) reduced and only slightly wider
than main portion of bone; (2) distinctly expanded
into somewhat square plate with irregular margins
(CI = 1.000; RI = 1.000).
The anterior portion of the maxilla in most species
of Sternarchorhynchus is moderately expanded into a
plate-like region (state 0; Fig. 4A) with a similar
condition also present amongst the examined out-
group species in the included species of Apteronotus,
along with Orthosternarchus tamandua (Hilton et al.,
2007: fig. 12), Sternarchorhamphus muelleri and Ster-
narchogiton labiatus. Sternarchorhynchus axelrodi
and S. mormyrus have that portion of the maxilla
proportionally further expanded into an approxi-
mately square plate with irregular margins (state 2;
Fig. 4B). Two other species of Sternarchorhynchus (S.
goeldii, S. oxyrhynchus) alternatively have the ante-
rior portion of the maxilla reduced in size relative to
the conditions present in most congeners, with that
region of the bone only slightly higher vertically than
are the proximate posterior portions of the maxilla
(state 1; Fig. 4C).
Platyurosternarchus has a highly expanded maxilla
(Mago-Leccia, 1994: fig. 23d) of a form unique within
the Apteronotidae (see discussion in de Santana &
Vari, 2009). This renders it impossible to code
Platyurosternarchus for the form of the anterior
portion of the maxilla. The maxilla in Sternar-
chorhamphus muelleri is anteriorly distinctly
expanded (Mago-Leccia, 1994: fig. 23h; Campos-da-
Paz, 1995: fig. 4), similarly rendering it impossible to
code that species for this character.
7. Form of ventral margin of maxilla: (0) relatively
smooth; (1) with distinct concavity (CI = 0.500;
RI = 0.900).
Although there occurs a pronounced diversity in the
overall forms of the maxilla across the Apteronotidae
(Mago-Leccia, 1994: fig. 23), most species in the
family (e.g. Sternarchorhamphus muelleri, Campos-
da-Paz, 1995: fig. 4), along with S. goeldii and S.
oxyrhynchus, have a smooth, variably convex ventral
margin of the main body of the bone (state 0; Fig. 4C).
Other examined Sternarchorhynchus species alterna-
tively, have distinct concavities along the main body
of the maxilla (state 1; Fig. 4A, B). Such a concavity
of the maxilla is also present in Orthosternarchus
tamandua (Hilton et al., 2007: fig. 12) amongst the
examined outgroups.
LOWER JAW
8. Extent of fleshy pad at anterior of dentary: (0)
absent or only slightly developed; when present not
overlapping tip of snout in closed mouth; (1) well-
developed, dorsally directed, and overlapping tip of
snout in closed mouth (CI = 1.000; RI = 1.000).
The anterior portion of the fleshy covering of the
dentary is slightly to moderately developed in out-
groups to Sternarchorhynchus along with most
members of the genus (state 0; Fig. 1B). Sternarcho-
rhynchus goeldii and S. oxyrhynchus, in contrast,
have a very well-developed, somewhat distally
pointed, fleshy pad at the anterodorsal limit of the
dentary (state 1; Fig. 1A). This dorsally directed pad
overlaps the anterior portion of the snout when the
mouth is closed.
9. Coronomeckelian bone: (0) present in juveniles
and adults; (1) present as small rounded ossification
in smaller specimens but absent in adults (CI = 1.000;
RI = 1.000).
The coronomeckelian bone is typically present in
most gymnotiforms and indeed most fishes. In P.
crypticus and P. macrostoma the coronomeckelian is
an anteroposteriorly elongate ossification running
along the dorsal margin of the anguloarticular and
the posterior portion of the well-developed Meckel?s
cartilage (Fig. 5). Comparable overall morphologies of
the bone occur in the other outgroup taxa in this
Figure 4. Maxilla of A, Sternarchorhynchus roseni,
MCNG 52591; B, Sternarchorhynchus mormyrus, USNM
306843, and C, Sternarchorhynchus goeldii, MCZ 46887;
left side, lateral view; larger stippling represents cartilage.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 233
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
analysis [A. albifrons, A. cuchillo, A. rostratus, ?A.?
apurensis, Orthosternarchus tamandua (Hilton et al.,
2007: fig. 12b), Sternarchella orthos, and Sternar-
chorhamphus muelleri (Campos-da-Paz, 1995: fig. 5)].
A small, round ossification positionally comparable to
the coronomeckelian bone of other gymnotiforms is
present in an approximately 40 mm TL specimen of
an unidentified species of Sternarchorhynchus stew-
arti. That element is comparable to the form of that
bone in adults of some genera of the Apteronotidae
(e.g. Sternarchogiton labiatus).
Adults of all species of Sternarchorhynchus exam-
ined osteologically neither have any indication of the
coronomeckelian bone (state 1; Figs 6, 7), nor do they
retain a residual cartilage mass in the area primi-
tively occupied by that ossification. The space occu-
pied in outgroups by the coronomeckelian bone and
Meckel?s cartilage is filled in Sternarchorhynchus by
the dramatically anteriorly expanded anguloarticular
characteristic of that genus (Figs 6, 7; see character
16).
Although the coronomeckelian bone was present in
all non-Sternarchorhynchus gymnotiforms examined
in this study, Mago-Leccia (1978: 36) reported that
the element was of small size and ?not ossified in some
specimens? [our translation] of Eigenmannia virescens
of the family Sternopygidae. It is uncertain whether
that statement indicates that the coronomeckelian is
present as a cartilaginous precursor to the bone or
that the element is completely absent in the individu-
Figure 5. Lower jaw of Platyurosternarchus macrostoma, FMNH 100730; left side, medial view, anterior to right; larger
stippling represents cartilage.
Figure 6. Lower jaw of Sternarchorhynchus goeldii, MCZ 46887; left side, medial view, anterior to right.
234 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
als in question. Regardless, the Sternopygidae is not
phylogenetically proximate to Sternarchorhynchus
and the absence of the ossification in a species of
Eigenmannia is homoplastic relative to the condition
in Sternarchorhynchus.
10. Meckel?s cartilage: (0) present and well devel-
oped; (1) well developed in smaller individuals, but
ontogenetically reduced and distinctly smaller in
adults (CI = 1.000; RI = 1.000).
Meckel?s cartilage is well developed across gymno-
tiforms and immediate outgroups to Sternarchorhyn-
chus [Orthosternarchus tamandua (Hilton et al.,
2007: fig. 12b), Platyurosternarchus (Fig. 5), Sternar-
chorhamphus muelleri (Campos-da-Paz, 1995: fig. 5)];
a condition comparable to that in most fishes. Within
the Gymnotiformes, Meckel?s cartilage most often has
the form of an anteriorly attenuating body arising
posteriorly from a distinct process on the medial wall
of the anteromedial process of the anguloarticular
and terminating anteriorly along the medial surfaces
of that bone and the dentary (Fig. 5; Chardon & De
La Hoz, 1974: fig. 6). Meckel?s cartilage undergoes a
progressive ontogenetic reduction in the species of
Sternarchorhynchus. The cartilage is present and
relatively well developed in small cleared and stained
specimens of approximately 30 mm TL. At that body
size, the cartilage arises from a distinct process that
projects from the medial wall of the anguloarticular
and then extends anteriorly to terminate a short
distance posterior of the dentary symphysis. The
notable difference in the form of Meckel?s cartilage at
that body size relative to the condition in outgroups is
that in Sternarchorhynchus the cartilage is distinctly
narrower vertically even at its highest portion proxi-
mate to its contact with the process on the medial
wall of the anguloarticular. At approximately 110 mm
TL, the cartilage in cleared and stained preparations
of Sternarchorhynchus is reduced vertically to a very
narrow band that arises posteriorly at the bony
process of the medial wall of the anguloarticular.
However, larger examined cleared and stained speci-
mens of the genus (approximately 115 mm TL) have
the cartilage reduced to a small, very narrow band
limited to the anterior quarter of the anguloarticular
and falling far short posteriorly of the position of the
process on the medial wall of the anguloarticular in
smaller specimens (state 1). Individuals of 225 mm
TL show no indication of that process on the angu-
loarticular. This ontogenetic reduction of Meckel?s
cartilage in the species of Sternarchorhynchus paral-
lels the pronounced anterior development of the angu-
loarticular in the genus, which in adults fills the
space occupied by Meckel?s cartilage in outgroups
(Figs 6, 7).
11. Relative lengths of posterodorsal and poster-
oventral processes of dentary: (0) posterodorsal
process shorter than ventrolateral process; (1) pos-
terodorsal and posteroventral processes of approxi-
mately same length (CI = 0.500; RI = 0.875).
Proximate outgroups to Sternarchorhynchus
[Orthosternarchus tamandua (Hilton et al., 2007:
fig. 12), P. crypticus, P. macrostoma (Fig. 5), Sternar-
chorhamphus muelleri (Campos-da-Paz, 1995: fig. 5)]
along with other gymnotiforms have a posterodorsal
process of the dentary extending dorsal of the angu-
loarticular that is, in turn, distinctly shorter than the
posteroventral process of the dentary. The latter
process runs ventral to the anguloarticular and some-
times along at least a portion of the ventral margin of
the retroarticular (state 0; Fig. 5) (for conditions in
some more distantly related gymnotiform taxa see
Mago-Leccia, 1978: fig. 8; Mago-Leccia et al., 1985:
fig. 3; Albert, 2001: fig. 10). The species of Sternar-
chorhynchus alternatively have posterodorsal and
posteroventral processes of the dentary of approxi-
mately identical lengths or in some instances with the
dorsal process slightly longer (Figs 6, 7). This condi-
tion is approximated in Sternarchella orthos (Lund-
Figure 7. Lower jaw of Sternarchorhynchus mareikeae, INPA 22901; left side, medial view, anterior to right.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 235
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
berg et al., 1996: fig. 3c) amongst the outgroup taxa of
this analysis. That species is, however, not closely
related to Sternarchorhynchus (Albert, 2001) and the
presence of this similar condition in these taxa is
homoplastic.
12. Form of posteroventral process of dentary: (0)
posteroventral process of dentary relatively robust
and triangular overall; (1) posteroventral process of
dentary very narrow and in form of elongate narrow
strut of bone (CI = 1.000; RI = 1.000).
The posteroventral process of the dentary that
extends ventral of the anterior portion of the angu-
loarticular is typically a relatively robust process in
gymnotiforms including proximate outgroups such as
Orthosternarchus tamandua (Hilton et al., 2007:
fig. 12), both species of Platyurosternarchus (Fig. 5),
and Sternarchorhamphus muelleri (Campos-da-Paz,
1995: fig. 4). That morphology also occurs in the other
outgroup apteronotids included in this study.
Amongst all of those taxa, the process is either rela-
tively broad vertically along most of its anteroposte-
rior extent or gradually tapers to a point distally with
a resultant overall triangular morphology (Mago-
Leccia, 1978: fig. 8; Mago-Leccia et al., 1985: fig. 3;
Albert, 2001: fig. 10). The species of Sternarchorhyn-
chus have the posteroventral process of the dentary
dramatically restructured into a very narrow strut of
bone that borders a major portion of the ventral
margin of the anteroposteriorly elongate anguloar-
ticular (Figs 6, 7).
13. Posterior limit of posteroventral process of
dentary: (0) posteroventral process of dentary reach-
ing margin of posteroventral process of anguloarticu-
lar; (1) posteroventral process of dentary not reaching
margin of posteroventral process of anguloarticular
(CI = 0.200; RI = 0.200).
As mentioned under character 12, the posteroven-
tral portion of the dentary of Sternarchorhynchus is
a narrow, elongate process bordering the ventral
margin of the anguloarticular (Fig. 6). The posterior
extent of this process of the dentary varies
within Sternarchorhynchus, with some species
having the posterior terminus of the process falling
short of the point where the posteroventral process
of the anguloarticular arises from the main
body of that ossification (state 1; Fig. 7). All other
species in Sternarchorhynchus (Campos-da-Paz,
2000: fig. 6, for condition in S. mesensis) have the
posteroventral process of the dentary extending
further posteriorly (state 0; Fig. 6), with resultant
contact of the posteroventral process of the dentary
with the posteroventral process of the angulo-
articular. A comparable contact between those ele-
ments occurs in Orthosternarchus tamandua (Hilton
et al., 2007: fig. 12), Sternarchorhamphus muelleri
(Campos-da-Paz, 1995: fig. 4), the species of
Platyurosternarchus, and the more distant out-
groups of this analysis (state 0).
14. Position of articulation between quadrate and
dorsal surface of lower jaw: (0) located in region of
articulation of anguloarticular and retroarticular,
with anterodorsal portion of retroarticular contribut-
ing to joint of lower law with quadrate; (1) located
distinctly anterior to region of articulation of angu-
loarticular and retroarticular, with anterodorsal
portion of retroarticular well separated from joint of
lower law with quadrate (CI = 1.000; RI = 1.000).
In Orthosternarchus tamandua (Hilton et al., 2007:
fig. 12) and Sternarchorhamphus muelleri (Campos-
da-Paz, 1995: figs 4, 5) the articulation of the articu-
lar condyle of the quadrate with the lower jaw is via
an articular socket positioned along the posterodorsal
margin of the jaw. In these species, the socket is
situated along the dorsal portion of the joint between
the anguloarticular and the retroarticular. Such a
form of the articular socket occurs in other gymnoti-
forms (e.g. Rhabdolichops, Mago-Leccia, 1978: fig. 8)
and is apparently the primitive condition for the
Apteronotidae. In both Sternarchorhynchus and
Platyurosternarchus, the area of quadrate?lower jaw
articulation is shifted anteriorly relative to the joint
between the anguloarticular and retroarticular. As a
result, the articular socket on the lower jaw is formed
solely by a portion of the posterodorsal region of the
anguloarticular (Figs 5?7) with a distinct separation
of the anterodorsal corner of the retroarticular and
the quadrate?lower jaw articulation.
The degree of separation of the retroarticular from
the joint between the lower jaw and quadrate
increases ontogenetically in both Platyurosternarchus
and Sternarchorhynchus. Smaller specimens of both
Platyurosternarchus (P. crypticus, approximately
90 mm TL) and Sternarchorhynchus (Sternarchorhyn-
chus cf. stewarti, approximately 40 mm TL) have the
quadrate?lower jaw articulation proportionally closer
to the anguloarticular?quadrate joint than in larger
individuals of each species or adults of congeners.
An articulation of the quadrate solely with the
anguloarticular resolves as a synapomorphy for
Platyurosternarchus and Sternarchorhynchus under
the results of this study (see also character 15). This
condition is also present in A. albifrons, A. cuchillo, A.
rostratus, ?A.? apurensis, Sternarchella orthos, and
Sternarchogiton labiatus amongst the outgroups
included in this analysis. The presence of this feature
in these outgroup taxa is homoplastic to the condition
in Platyurosternarchus and Sternarchorhynchus
under present hypotheses of relationships within the
Gymnotiformes (Albert, 2001).
15. Degree of separation along dorsal margin of
anguloarticular between joint for articulation with
quadrate and anguloarticular-retroarticular joint: (0)
236 C. D. DE SANTANA and R. P. VARI
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distance approximately equal to width of articular
facet on anguloarticular that contacts quadrate; (1)
distance approximately about 4?4.5 times width of
articular facet on anguloarticular that contacts quad-
rate (CI = 1.000; RI = 1.000).
The site of articulation of the lower jaw with the
quadrate is restricted to the anguloarticular in both
Platyurosternarchus and Sternarchorhynchus (charac-
ter 14), albeit differing in relative positions in the
genera. Platyurosternarchus crypticus and P. macros-
toma have a shorter, albeit, distinct separation of the
condyle from the joint between the anguloarticular and
retroarticular (state 0; Fig. 5). In contrast, the species
of Sternarchorhynchus along with the outgroups A.
albifrons, A. cuchillo, A. rostratus, ?A.? apurensis, Ster-
narchella orthos, and Sternarchogiton labiatus have a
pronounced separation between these two landmarks
(state 1; Figs 6, 7). This character could not be coded
for Orthosternarchus tamandua and Sternarchorham-
phus muelleri, in which the articular condyle on the
lower jaw is formed jointly by the anguloarticular and
retroarticular rather than being restricted to the
dorsal margin of the anguloarticular.
16. Form of anterior portion and medial surface of
anguloarticular: (0) anterior portion of anguloarticu-
lar broad with medial surface of bone having distinct
process at posterior terminus of Meckel?s cartilage; (1)
anterior portion of anguloarticular distinctly pointed
with medial surface of bone unelaborated (CI = 1.000;
RI = 1.000).
The anterior portion of the anguloarticular that
articulates with the posterior region of the dentary is
relatively broad in most gymnotiforms (e.g. Albert,
2001: fig. 10) including the proximate outgroups to
Sternarchorhynchus in this study [Orthosternarchus
tamandua (Hilton et al., 2007: fig. 13), the species of
Platyurosternarchus, and Sternarchorhamphus muel-
leri]. All of the outgroups also have a distinct process
that arises from the medial surface of the anguloar-
ticular and serves as the posterior limit of Meckel?s
cartilage (Fig. 5). Amongst the species of Sternarcho-
rhynchus, the anterior portion of the anguloarticular
has instead a distinctly anteriorly tapering overall
triangular form (Figs 6, 7). Although a triangular
anterior portion of the anguloarticular also occurs in
some members of the Sternopygidae (e.g. Rhabdoli-
chops; Mago-Leccia, 1978: fig. 8), the form of region is
not distinctly anteriorly attenuate in those species.
Those members of the Sternopygidae are, further-
more, distantly related to Sternarchorhynchus
(Albert, 2001) and the similarities between these taxa
and Sternarchorhynchus in this character are clearly
homoplastic. As discussed under character 16, larger
individuals of the species of Sternarchorhynchus have
an unelaborated medial surface of the anguloarticu-
lar. The ontogenetic loss in Sternarchorhynchus of the
process present in that region of the anguloarticular
in other gymnotiforms correlates with the pronounced
reduction of Meckel?s cartilage in adults of all species
of the genus (character 10).
17. Location of posterior terminus and form of pos-
teroventral portion of the anguloarticular: (0) angu-
loarticular terminating posteriorly approximately at
vertical through dorsal portion of joint between angu-
loarticular and retroarticular and without distinct
posteriorly attenuating process extending under ret-
roarticular; (1) anguloarticular terminating posteri-
orly at, to distinctly posterior of, vertical through
dorsal portion of joint between anguloarticular and
retroarticular and with distinct, posteriorly attenuat-
ing process extending along anterior margin of ret-
roarticular (CI = 1.000; RI = 1.000).
Two highly divergent forms of the posteroventral
portion of the anguloarticular are found in Sternar-
chorhynchus and the other gymnotiforms incorpo-
rated into this study. In Sternarchorhamphus
muelleri (Campos-da-Paz, 1995: fig. 5) and Orthoster-
narchus tamandua (Hilton et al., 2007: fig. 12b) the
posteriormost portion of the anguloarticular is situ-
ated within the dorsal portion of the joint between the
anguloarticular and retroarticular. This portion of the
anguloarticular is incorporated into the socket receiv-
ing the articular condyle of the quadrate. The retroar-
ticular in these two species has an anteriorly directed
process extending under the posterior portion of the
anguloarticular (state 0) with this condition also
present in the other outgroups. The process is mod-
erately developed in Orthosternarchus tamandua
(Hilton et al., 2007: fig. 12) and extends further ante-
riorly in Sternarchorhamphus muelleri. The species of
Platyurosternarchus and Sternarchorhynchus have
the posteroventral portion of the anguloarticular
extending further posteriorly, forming a distinct pos-
teriorly attenuating process that extends under the
anterior portion of the retroarticular (state 1; Figs 5?
7). As such, the posterior terminus of the posteroven-
tral portion of the anguloarticular in those genera is
situated posterior of the vertical through the dorsal
portion of the joint between the anguloarticular and
the retroarticular.
18. Position of posterior limit of dentary: (0) poste-
rior limit of dentary located distinctly anterior of
vertical through vertical component of orbitosphe-
noid; (1) posterior limit of dentary located along ver-
tical through vertical component of orbitosphenoid
(CI = 0.500; RI = 0.800).
As discussed under characters 14 and 15, consider-
able variation occurs amongst the genera of interest
in diverse aspects of the articulation of the lower jaw
with the suspensorium. An additional difference
reflective of the broader details of the arrangement of
the bones of the head in these taxa involves the
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 237
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
location of the position of the posteriormost point on
the dentary with respect to the neurocranium. In S.
goeldii and S. oxyrhynchus, along with the outgroups
Orthosternarchus tamandua, P. crypticus, P. macros-
toma, and Sternarchorhamphus muelleri, the poste-
rior limit of the dentary lies considerably anterior of
the vertical running through the vertically aligned
section of the orbitosphenoid (state 0). In the remain-
ing species of Sternarchorhynchus the posterior ter-
mination of the dentary is more posteriorly positioned
relative to the orbitosphenoid, being situated along,
or posterior of, the vertical through the vertically
orientated anterior portion of the orbitosphenoid
(state 1). State 1 is also present amongst the out-
groups in Sternarchella orthos and Sternarchogiton
labiatus.
DENTITION
19. Form of teeth in upper and lower jaws: (0) teeth
proportionally elongate with relatively little change
in width other than distally and with slight posterior
curvature distally; (1) teeth distinctly wider basally
and tapering progressively to distinctly posteriorly
recurved distal portion (CI = 1.000; RI = 1.000).
Species of Sternarchorhynchus and its immediate
outgroup species, P. crypticus and P. macrostoma,
along with the basal apteronotids Orthosternarchus
tamandua (Hilton et al., 2007: fig. 12) and Sternar-
chorhamphus muelleri have teeth arranged in one or
more rows along the dorsal portion of the dentary.
These taxa also bear a patch of comparable dentition
on the ventral surface of the premaxilla other than for
the species of Platyurosternarchus, which lack upper
jaw dentition. The tooth form differs amongst these
taxa, with Orthosternarchus tamandua and Sternar-
chorhamphus muelleri having relatively elongate
teeth on each jaw (state 0). The teeth in these genera
become only slightly narrower along most of their
length and terminate in a slightly posteriorly
recurved point [tooth form termed villiform by Albert
(2001: 16) and some other authors). Sternarchorhyn-
chus alternatively has the teeth in both jaws tapering
to a pronounced degree from proportionally wider
bases with the distal curvature more developed (state
1). A similar form of distally tapering dentition occurs
in the lower jaw of the species of Platyurosternarchus.
However, this genus has an edentulous premaxilla.
Such a form of dentition is also present in both jaws
of the other outgroups included in the analysis except
Orthosternarchus and Sternarchorhamphus.
20. Location of area of attachment of teeth on
dentary: (0) teeth attaching to exterior surface of
dentary; (1) teeth attaching to interior surface of
dentary (CI = 1.000; RI = 1.000).
Attachment of the teeth on the dentary is consis-
tently on the inner surface of the dentary in the
species of Sternarchorhynchus, Sternarchorhamphus
muelleri (Campos-da-Paz, 1995: fig. 5), Orthosternar-
chus tamandua (Hilton et al., 2007: fig. 12), and the
other apteronotid outgroups in this study other than
P. crypticus and P. macrostoma. The dentition in
Platyurosternarchus instead attaches to the outer
surface of the dentary. Megadontognathus, an apter-
onotid genus not amongst the outgroup taxa of this
study, has teeth arising from the outer surface of the
dentary. Dentary dentition in this genus is limited to
the posterior portion of the dorsal margin of the
dentary (Mago-Leccia, 1994: fig. 58), whereas
Platyurosternarchus has the dentition restricted to
the anterior one-third of the dorsal margin of the
bone. These positional differences indicate nonhomol-
ogy of the dentition on the outer margin of the
dentary in the two genera; a hypothesis supported by
the pronounced phylogenetic separation of Megadon-
tognathus and Platyurosternarchus (Albert, 2001).
PALATINE ARCH
21. Degree of development of anterior portion of pala-
toquadrate cartilage: (0) moderately to well devel-
oped; (1) poorly developed and reduced to narrow,
somewhat thread-like process (CI = 1.000; RI = 1.000).
The anterior portion of the palatoquadrate cartilage
(the pars autopalatine of Hilton et al., 2007: fig. 11)
ranges from moderately to well developed in most of
the apteronotids incorporated into this study.
Although the palatoquadrate cartilage is somewhat
reduced in Platyurosternarchus relative to the condi-
tion in some other apteronotids, the cartilage remains
an overall moderately well-developed, triangular
structure (Fig. 8). Sternarchorhynchus species have
the palatoquadrate cartilage much further reduced,
resulting in a small structure (Figs 9, 10) sometimes
having an almost thread-like form. Such a reduction
is unique to Sternarchorhynchus amongst the taxa in
this analysis.
22. Position of endopterygoid: (0) endopterygoid
positioned along dorsomedial margin of lower jaw
with no, or limited, overlap by ventral portion of
endopterygoid of posterodorsal process of dentary and
posterodorsal region of anguloarticular; endoptery-
goid largely positioned above dorsal margins of
dentary and anguloarticular; (1) endopterygoid posi-
tioned along medial surface of dentary and anguloar-
ticular with dorsal margin of endopterygoid located
distinctly ventral of dorsal margins of dentary and
anguloarticular (CI = 1.000; RI = 1.000).
Most members of the Gymnotiformes have the
endopterygoid (the mesopterygoid or entopterygoid of
some previous authors) positioned distinctly dorsal of
the dorsal margin of the bones of the lower jaw (e.g.
A. albifrons, Chardon & De La Hoz, 1974: fig. 20;
238 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Figure 8. Suspensorium and opercular series of Platyurosternarchus macrostoma, FMNH 100730; left side, lateral view,
anterior to left; larger stippling represents cartilage.
Figure 9. Suspensorium and opercular series of Sternarchorhynchus chaoi, INPA 20851; left side, lateral view, anterior
to left; larger stippling represents cartilage.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 239
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
state 0) or demonstrate limited overlap of the endo-
pterygoid and the dorsal portions of the dentary and
anguloarticular (e.g. species of Platyurosternarchus,
Sternarchorhamphus muelleri, and more distant out-
groups in the analysis; also state 0). The palatine arch
is shifted ventrally relative to the lower jaw in the
species of Sternarchorhynchus as part of the revamp-
ing necessitated by space restrictions along the verti-
cal axis in the elongate tubular snout characteristic of
the genus. One of the changes required to accommo-
date a dorsoventrally narrow snout is the shift dorsally
of the lower jaw relative to the endopterygoid. This
repositioning results in the endopterygoid being situ-
ated medial to the dentary and anguloarticular in
Sternarchorhynchus (state 1). The dorsal margin of the
endopterygoid is consequently positioned ventral of
the dorsal border of the dorsal portions of the dentary
and anguloarticular; a unique arrangement of these
elements amongst examined gymnotiforms.
23. Form of anterior portion of endopterygoid: (0)
anterior portion of bone attenuating, but with ante-
rior region approximately as wide transversely as
high; (1) anterior portion of bone very narrow and
compressed transversely and distinctly higher than
wide (CI = 1.000; RI = 1.000).
All examined outgroup gymnotiforms have a dors-
oventrally higher anterior portion of the endoptery-
goid, which, nonetheless, extends medially to an
extent such that it is approximately as wide trans-
versely as it is high (state 0; Fig. 8). Sternarchorhyn-
chus species have an unusual endopterygoid that is
very narrow along the anteroposterior axis and
reduced along the transverse plane. As a consequence,
the endopterygoid is proportionally higher vertically
than wide transversely state 1; (Figs 9, 10).
An endopterygoid with the anterior portion larger
than the posterior section of the bone was proposed as
a synapomorphy for Platyurosternarchus, Sternarcho-
rhynchus, and Ubidia by Triques (2005; ossification
termed the mesopterygoid therein). The landmark
delimiting those portions of the bone was not identi-
fied. That issue aside, although the endopterygoid is
distinctly elongate in Sternarchorhynchus (Fig. 9), the
proportional length of the bone in Platyurosternar-
chus (Fig. 8; Albert, 2001: fig. 31a) is comparable to
that not only in Ubidia (Miles, 1945: fig. 11) but also
species of Apteronotus (e.g. A. albifrons, Chardon &
De La Hoz, 1974: fig. 6; Apteronotus bonapartii,
Hilton & Cox-Fernandes, 2006: fig. 5). Elongation of
the element is thus of broader occurrence and a more
Figure 10. Suspensorium and opercular series of Sternarchorhynchus goeldii, MCZ 46887; right side, lateral view,
anterior to left; larger stippling represents cartilage.
240 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
encompassing analysis is necessary to determine the
phylogenetic level at which it is applicable.
24. Form of posterior portion of endopterygoid: (0)
relatively high vertically and broadly overlapping
dorsal portion of quadrate and anterodorsal region of
metapterygoid; not fused to quadrate or metaptery-
goid; (1) vertically reduced to very elongate, some-
what horizontally aligned process extending along
and either tightly attached to lateral surface of quad-
rate and metapterygoid or fused to quadrate
(CI = 1.000; RI = 1.000).
The typical form of the posterior portion of the
endopterygoid in gymnotiforms including Orthoster-
narchus tamandua (Hilton et al., 2007: fig. 11), the
species of Platyurosternarchus (Albert, 2001: fig. 31a),
Sternarchorhamphus muelleri (Albert, 2001: fig. 31b),
and examined outgroups is a vertically relatively
expansive ossification closely applied and tightly
attached to the lateral surface of portions of the
quadrate and metapterygoid (state 0; Fig. 8). Sterna-
rchorhynchus has the vertical extent of the posterior
region of the endopterygoid dramatically reduced to
an elongate process extending along the middle of the
lateral portions of the quadrate and metapterygoid
(state 1; Figs 9, 10). The reduction of the primitively
broad contact between the overlapping endopterygoid,
quadrate, and metapterygoid and the consequent
decrease in the area of contact of the entopterygoid
with the posterior elements of the palatine arch is
offset by the very tight association of the reduced
posterior portion of the endopterygoid with the lateral
surface of the quadrate in the species of Sternarcho-
rhynchus. Maximal connectivity of the endopterygoid
and quadrate is achieved in S. goeldii and S. oxyrhyn-
chus where these bones are fused into a single ossi-
fication without trace in adults of the original line of
contact (Fig. 10; see character 25).
25. Association of quadrate and endopterygoid: (0)
bones closely applied but separate; (1) bones fused
(CI = 1.000; RI = 1.000).
The quadrate and endopterygoid are closely applied
to each other but separate in examined outgroup
gymnotiforms and in all species of Sternarchorhyn-
chus other than S. goeldii and S. oxyrhynchus (state
0; Fig. 9). These two species have the quadrate and
endopterygoid fused into a single anteroposteriorly
elongate ossification without any indication of the
original joint between those elements (state 1;
Fig. 10).
26. Ascending process of endopterygoid: (0) absent;
(1) present (CI = 0.250; RI = 0.500).
Diverse gymnotiforms have a variably elongate,
dorsally directed ascending process of the endoptery-
goid arising from the dorsal surface of that bone
(e.g. Sternarchella sima, Albert, 2001: fig. 31c). Such
a process is present in S. mormyrus but absent
across all of the other members of the genus exam-
ined osteologically (state 1). The feature was, none-
theless, included in the analysis because it may
serve to define a small assemblage of species once
the remaining recognized members of the genus are
examined osteologically or further species of Sterna-
rchorhynchus are described and evaluated as to
their phylogenetic relationships. Within proximate
outgroups such an endopterygoid process is encoun-
tered in P. crypticus but is absent in P. macrostoma.
A comparable process is also present in smaller indi-
viduals of Sternarchorhamphus muelleri but is lost
ontogenetically. We were unable to code S. axelrodi
for this feature.
Possession of the process optimized as a synapo-
morphy for the clade consisting of Platyurosternar-
chus, Sternarchorhynchus, and Ubidia in the analysis
by Triques (2005) that included a limited number of
Sternarchorhynchus species. The process is only
present in one species in the genus and one of the two
species of Platyurosternarchus and as such does not
serve to unit those three genera.
27. Attachment area of pterygocranial ligament: (0)
limited to dorsal surface of endopterygoid; (1) involv-
ing both endopterygoid and quadrate (CI = 0.250;
RI = 0.727).
The pterygocranial ligament extends posterodor-
sally from the suspensorium to an attachment on the
orbitosphenoid. In examined outgroups along with S.
caboclo, Sternarchorhynchus chaoi, S. curvirostris, S.
curumim, S. goeldii, Sternarchorhynchus higuchii,
Sternarchorhynchus mendesi, S. mesensis, S.
mormyrus, S. oxyrhynchus, and S. roseni, the liga-
ment attaches onto the suspensorium solely via a
small dorsal process extending from the endoptery-
goid (state 0; Fig. 11A) that is best viewed from an
oblique dorsoventral angle. Sternarchorhynchus brit-
skii, Sternarchorhynchus cramptoni, S. gnomus, Ster-
narchorhynchus hagedornae, Sternarchorhynchus
inpai, Sternarchorhynchus jaimei, Sternarchorhyn-
chus mareikeae, Sternarchorhynchus montanus, Ster-
narchorhynchus retzeri, Sternarchorhynchus starksi,
S. stewarti, and S. severii instead have the quadrate
also contributing the attachment of the pterygocra-
nial ligament on the suspensorium. This attachment
site most often has the form of a dorsal process
extending along the surface of the dorsal process of
the entopterygoid and often completely overlapping
the corresponding portion of the entopterygoid from
medial view (state 1; Fig. 11B). We were unable to
code S. axelrodi for this feature from radiographs of
the type series.
28. Overall form of dorsal portion of quadrate: (0)
with relatively broad, anterodorsal plate-like process;
(1) without broad, anterodorsal plate-like process
(CI = 1.000; RI = 1.000).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 241
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Outgroup gymnotiforms in this study including the
immediate outgroups in this analysis (e.g. P. macros-
toma, Sternarchorhamphus muelleri; Albert, 2001:
fig. 31a, b) have a variably well-developed plate-like
process of the quadrate that extends dorsal of the
articular condyle that contacts the lower jaw (state 0;
Fig. 8). In the species of Sternarchorhynchus, the
quadrate is dorsoventrally shallower and lacks this
dorsal process on the bone (state 1; Figs 9, 10).
29. Form of dorsal margin of quadrate: (0) straight
to slightly convex; (1) concave (CI = 1.000; RI = 1.000).
A straight or convex dorsal margin along the plate-
like dorsal process of the quadrate typifies most gym-
notiforms including all proximate outgroups for
Sternarchorhynchus in this analysis [e.g. Orthoster-
narchus tamandua (Hilton et al., 2007: fig. 11); Ster-
narchorhamphus muelleri (Albert, 2001: fig. 31a, b)].
As described under character 28, Sternarchorhynchus
species have the quadrate reduced vertically. Sterna-
rchorhynchus axelrodi, S. goeldii, S. mormyrus, and
S. oxyrhynchus, nonetheless, retain a straight to
slightly convex dorsal margin of the reduced quadrate
comparable to the form of that portion of the ossifi-
cation in outgroups (state 0; Fig. 10). All other
members of Sternarchorhynchus have a distinctly
concave dorsal margin to the quadrate (state 1;
Fig. 9).
30. Form of posterolateral portion of quadrate: (0)
without lateral expansion; (1) with lateral expansion
into rounded ridge terminating posteriorly in articu-
lar facet (CI = 1.000; RI = 1.000).
Outgroups have the lateral surface of the quadrate
unelaborated (state 0), with the posterolateral region
of this bone overlapped laterally by the endopterygoid
[e.g. Orthosternarchus tamandua (Hilton et al., 2007:
fig. 11)]. The posterolateral portion of the quadrate is
Figure 11. Anterior portion of quadrate and associated structures of A, Sternarchorhynchus mormyrus, USNM 306843
(note: small bony process at base of pterygocranial ligament is part of endopterygoid), and B, Sternarchorhynchus retzeri,
FMNH 11515; showing differing contributions of bones to attachment areas for pterygocranial ligament; process of
endopterygoid shown in (A) is hidden by process of quadrate in (B); right side, medial view, anterior to left.
242 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
exposed laterally but unelaborated in all Sternarcho-
rhynchus species other than S. goeldii and S. oxy-
rhynchus and is consequently coded as state 0 for
these taxa (Fig. 9). Sternarchorhynchus goeldii and S.
oxyrhynchus bear a lateral expansion of the lateral
surface of the posterodorsal portion of the quadrate,
with the expanded region having the form of a raised,
laterally rounded, longitudinally aligned ridge termi-
nating in a distinct posterior facet (state 1; Fig. 10)
that articulates with a corresponding facet on the
anterior surface of the metapterygoid (see character
39).
31. Form of posteroventral margin of main body of
quadrate that receives anterior tip of symplectic: (0)
with distinct notch; notch open laterally and most
often also medially; (1) notch very small or absent and
when present enclosed laterally and medially by ver-
tical sheet of bone (CI = 0.333; RI = 0.500).
The narrow anterior portion of the symplectic fits
into a distinct concavity in the posteroventral margin
of the main body of the quadrate in proximate out-
groups to Sternarchorhynchus together with all exam-
ined members of the genus other than S. mormyrus
and perhaps S. axelrodi (state 0). In S. mormyrus the
anteriormost portion of the symplectic fits into a
dorsally open pocket bordered medially and laterally
by vertical bony processes arising from the quadrate
(state 1). Such a modification of the quadrate also
appears to be present in S. axelrodi based on radio-
graphs of several specimens of this species. Looking
to more distant outgroups, we find that state 1 is
present in A. albifrons, ?A.? apurensis, and Sternar-
chogiton labiatus. The character was included in the
analysis as a potential synapomorphy for S. axelrodi
and S. mormyrus that are herein proposed as sister
taxa and perhaps for other species not examined
osteologically in this study.
32. Position of area of articulation of symplectic
with quadrate: (0) anterior portion of symplectic
fitting into notch or bony pocket along posteroventral
margin of quadrate located anterior of ventral limit of
joint between quadrate and metapterygoid; (1) ante-
rior portion of symplectic fitting into notch or pocket
along posteroventral margin of quadrate located dis-
tinctly posterior of ventral limit of joint between
quadrate and metapterygoid (CI = 0.500; RI = 0.500).
The notch or pocket in the posteroventral portion of
the quadrate that accommodates the anterior tip of
the symplectic is located anterior to, distinctly ante-
rior of, the ventral terminus of the quadrate?
metapterygoid joint in examined outgroups to
Sternarchorhynchus and in all species in the genus
other than S. curvirostris, S. goeldii, and S. oxyrhyn-
chus (state 0; Fig. 9). These three species have the
articulation of these ossifications shifted distinctly
posteriorly relative to that landmark and situated
ventral of the metapterygoid (state 1; Fig. 12).
33. Lateral closure of notch along posteroventral
margin of quadrate that receives symplectic: (0)
present; (1) absent (CI = 0.250; RI = 0.500).
Outgroup taxa in the analysis along with S. axel-
rodi, S. britskii, S. curvirostris, S. curumim, S.
gnomus, S. goeldii, S. hagedornae, S. higuchii, S.
inpai, S. mareikeae, S. mendesi, S. montanus, S.
mormyrus, S. oxyrhynchus, S. severii, S. starksi, and
S. stewarti have the lateral portion of the notch in the
quadrate that receives the anterior tip of the sym-
plectic covered, or largely covered, by a thin sheet of
Figure 12. Posterior portion of quadrate, anterior portion of metapterygoid and symplectic, and adjoining bones in
Sternarchorhynchus curvirostris, USNM 163887; left side, lateral view, anterior to left; larger stippling represents
cartilage.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 243
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
bone arising from the main body of the quadrate
(state 0; Figs 10, 12). This thin bony sheet is absent in
S. caboclo, S. chaoi, S. cramptoni, S. jaimei, S. mesen-
sis, S. retzeri, and S. roseni (state 1; Fig. 9). A com-
parable bony sheet appears to be present in S.
axelrodi based on radiographs.
34. Overlap laterally of anteroventral corner of
metapterygoid by bony process of quadrate: (0)
absent; (1) present (CI = 0.333; RI = 0.600).
The anteroventral corner of the metapterygoid
proximate to the joint between this ossification and
the quadrate is laterally exposed in most gymnoti-
forms including all examined outgroups to
Sternarchorhynchus (state 0). Sternarchorhynchus
curvirostris, S. gnomus, S. hagedornae, S. higuchii, S.
mareikeae, and S. starksi have a further development
dorsally of the bony sheet such that it overlaps the
lateral surface of the notch in the posteroventral
portion of the quadrate. This expansion results in the
lateral overlap of the anteroventral corner of the
metapterygoid by the dorsal process of the quadrate
in these species (state 1; Fig. 12).
35. Location of posterior limit of posteroventral
process of quadrate: (0) when present, process termi-
nates approximately at, or slightly posterior of, ver-
tical through ventral portion of joint between
quadrate and metapterygoid; (1) process terminates
approximately at vertical through two-thirds of
length of metapterygoid or posterior of that point
(CI = 1.000; RI = 1.000).
Most gymnotiforms either lack a posteroventral
process of the quadrate that extends ventral of the
symplectic and over the anteroventral process of the
preopercle (e.g. Gymnotus carapo, Chardon & De La
Hoz, 1974: fig. 4) or have a relatively short process
that terminates approximately at, or slightly poste-
rior of, the vertical through the ventral portion of the
area of contact of the metapterygoid and quadrate
(state 0). The latter condition is present in all exam-
ined outgroups to Sternarchorhynchus [e.g. Orthoster-
narchus tamandua (Hilton et al., 2007: fig. 11);
Platyurosternarchus (Albert, 2001: fig. 31a); Sternar-
chorhamphus muelleri (Albert, 2001: fig. 31b)]. Ster-
narchorhynchus species have a much more elongate
posteroventral process of the quadrate. This process
extends from the body of the ossification as a narrow
flange of bone running ventral of the symplectic to a
point at least as far posterior as the vertical located
two-thirds of the distance along the length of the
metapterygoid (state 1; Figs 9, 10, 12).
36. Overall form of symplectic: (0) symplectic rela-
tively slender, with height of posteriormost portion of
bone approximately one-fifth length of bone; (1) sym-
plectic proportionally vertically higher, with height of
posteriormost portion of bone approximately one-
third length of bone (CI = 0.250; RI = 0.625).
Species of Sternarchorhynchus other than S. axel-
rodi, S. goeldii, S. mormyrus, and S. oxyrhynchus
have a relatively slender symplectic that from a
lateral view gradually increases posteriorly in its
vertical extent. As a consequence, the height of the
posteriormost portion of the symplectic is approxi-
mately one-fifth of its length (state 0). This symplectic
form also occurs in A. cuchillo, A. rostratus, Orthoster-
narchus tamandua (Hilton et al., 2007: fig. 11), P.
crypticus, and Sternarchorhamphus muelleri in the
outgroups (state 0). Sternarchorhynchus axelrodi, S.
chaoi, S. goeldii, S. mormyrus, and S. oxyrhynchus
have instead a distinctly more posterodorsally angled
dorsal margin of the symplectic with a resultant
greater disparity in the height of the anterior versus
posterior portions of the bone (state 1). State 1 is
present amongst the examined outgroups in A. albi-
frons, ?A.? apurensis, P. macrostoma, Sternarchella
orthos, and Sternarchogiton labiatus.
37. Anterodorsally directed process on dorsal
margin of symplectic: (0) absent; (1) present
(CI = 0.250; RI = 0.667).
The dorsal margin of the symplectic is straight to
variably irregular in outgroups to Sternarchorhyn-
chus (Hilton et al., 2007: fig. 11, for condition in
Orthosternarchus tamandua) and nearly all species of
the genus (state 0; Fig. 9). Sternarchorhynchus
cramptoni, S. curumim, S. curvirostris, S. goeldii, S.
hagedornae, S, mareikeae, S. oxyrhynchus, S. retzeri,
S. starksi, and S. stewarti rather have the dorsal
portion of the symplectic elaborated into an anteriorly
and slightly medially directed process (state 1;
Figs 10, 12).
38. Form of metapterygoid: (0) approximately trian-
gular overall; (1) somewhat to distinctly horizontally
elongate and approximately quadrilateral (CI = 1.000;
RI = 1.000).
The metapterygoid in outgroups to Sternarchorhyn-
chus is approximately triangular [e.g. Orthosternar-
chus tamandua (Hilton et al., 2007: fig. 11);
Platyurosternarchus (Albert, 2001: fig. 31a); Sternar-
chorhamphus (Albert, 2001: fig. 31b)] with the poste-
rior portion tapering to a variably distinct point (state
0; Fig. 8). Species of Sternarchorhynchus, in contrast,
have a more elongate metapterygoid with an overall
quadrilateral form (state 1; Figs 9, 10).
39. Form of lateral surface of dorsal portion of
metapterygoid: (0) overall flat or gently convex with
minimal thickening; (1) with distinct rounded lateral
ridge terminating anteriorly in well-developed articu-
lar surface (CI = 1.000; RI = 1.000).
Outgroups to Sternarchorhynchus have the poste-
rior portion of the endopterygoid overlapping the
anterodorsal region of the metapterygoid, with the
latter ossification having a smooth lateral surface
[e.g. Orthosternarchus tamandua (Hilton et al., 2007:
244 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
fig. 11a)]. The dorsal portion of the metapterygoid in
Sternarchorhynchus is not overlapped by the endop-
terygoid; however, all members of the genus other
than S. goeldii and S. oxyrhynchus have the exposed
portion of the metapterygoid unelaborated laterally or
bearing at most some minor ridges and/or expansions
on that surface (state 0; Fig. 9). Both S. goeldii and S.
oxyrhynchus have a lateral elaboration of the dorso-
lateral portion of the metapterygoid expanded into a
thickened, laterally rounded, anteroposteriorly
aligned ridge. This metapterygoid expansion is par-
ticularly well developed anteriorly, where it forms a
broad facet that articulates with a corresponding
process of the quadrate (state 1, Fig. 10; see also
character 30).
40. Association of posterior tip of posteroventral
process of quadrate and dorsal margin of horizontal
arm of preopercle: (0) tip of posteroventral process of
quadrate positioned above dorsal margin of preo-
percle; (1) tip of posteroventral process of quadrate
fitting into variably developed notch along dorsal
margin of preopercle (CI = 1.000; RI = 1.000).
Outgroups to Sternarchorhynchus and S. goeldii, S.
oxyrhynchus, and S. mormyrus have the elongate
posteroventral process of the quadrate running along
and closely applied to the dorsal margin of the hori-
zontal arm of the preopercle. In that condition the tip
of the quadrate process is neither enveloped posteri-
orly nor dorsally by the preopercle (state 0; Fig. 10).
We were unable to code this feature for S. axelrodi.
All remaining species of Sternarchorhynchus have the
dorsal margin of the preopercle expanded dorsally in
the region posterior to the tip of the posteroventral
process of the quadrate. Consequently, the posterior-
most portion of the quadrate lies within a depression
along the dorsal margin of the preopercle (state 1;
Figs 9, 12). Species with this expansion often, but not
always, have the dorsally expanded portion of the
preopercle elaborated into an anterodorsally directed
process extending towards or over the tip of the
quadrate process, sometimes encompassing the tip.
41. Anterior extent of preopercle: (0) terminating
variably posterior of vertical through ventral portion
of joint between quadrate and metapterygoid; (1)
extending to location anterior of vertical through
ventral portion of joint between quadrate and metap-
terygoid (CI = 0.143; RI = 0.625).
Examined apteronotid outgroups and S. axelrodi, S.
chaoi, S. cramptoni, S. hagedornae, S. montanus, S.
mormyrus, and S. starksi have the horizontal arm of
the preopercle extending anteriorly to a point situated
distinctly posterior of the ventral portion of the
quadrate?metapterygoid joint (state 0; Figs 8, 9).
Sternarchorhynchus britskii, S. caboclo, S. curumim,
S. curvirostris, S. gnomus, S. goeldii, S. higuchii, S.
inpai, S. jaimei, S. mareikeae, S. mendesi, S. mesen-
sis, S. oxyrhynchus, S. retzeri, S. roseni, S. severii, and
S. stewarti instead possess an anteroposteriorly
longer horizontal arm of the preopercle terminating
anteriorly somewhat, to distinctly, anterior of the
vertical through the ventral portion of this joint (state
1; Fig. 10).
42. Form of laterosensory canal segment in vertical
arm of preopercle: (0) in form of two shallowly ante-
riorly concave segments; (1) in form of two deeply
anteriorly concave segments (CI = 0.167; RI = 0.545).
The portion of the laterosensory canal system in the
vertical arm of the preopercle in Sternarchorhynchus
has the form of two anteriorly concave segments that
join, or nearly meet, approximately midway along the
vertical length of the bone. Two major alternative
morphologies of this system occur in the genus. In S.
axelrodi, S. caboclo, S. chaoi, S. cramptoni, S.
curumim, S. goeldii, S. mormyrus, S. oxyrhynchus, S.
retzeri, and S. severii, the canals form deeply anteri-
orly convex arcs (state 1; Figs 9, 10, 13A). State 1 is
also present in ?A.? apurensis and P. macrostoma in
the outgroups. Sternarchorhynchus britskii, S. curvi-
rostris, S. gnomus, S. higuchii, S. hagedornae, S.
inpai, S. jaimei, S. mareikeae, S. mendesi, S. mesen-
sis, S. montanus, S. roseni, S. starksi, and S. stewarti
also have concave canal segments such as those in
congeners, but with the convexity of the laterosensory
canal segments much less pronounced and in the form
of distinctly shallow arcs (state 0; Fig. 13B). State 0 is
also present in the outgroups in the three examined
species of Apteronotus, Orthosternarchus tamandua,
P. crypticus, Sternarchella orthos, Sternarchogiton
labiatus, and Sternarchorhamphus muelleri.
43. Form of dorsal margin of opercle: (0) very
slightly concave to distinctly convex; (1) distinctly
concave (CI = 0.250; RI = 0.500).
Outgroups to Sternarchorhynchus have the dorsal
margin of the opercle ranging from very slightly
concave to distinctly convex, with the species of
Platyurosternarchus plus Sternarchorhamphus muel-
leri having slightly concave margins to the bone (state
0; Fig. 8). That condition also occurs amongst more
distant outgroups in A. albifrons, A. cuchillo, ?A.?
apurensis, and Sternarchogiton labiatus. Sternarcho-
rhynchus, in contrast, has the opercular margin dis-
tinctly concave (Figs 9, 10) with this condition (state
1) also present amongst outgroups in A. rostratus,
Orthosternarchus tamandua (Hilton et al., 2007:
fig. 11), and Sternarchella orthos (Lundberg et al.,
1996: fig. 5c).
44. Form of posterodorsal corner of opercle: (0)
rounded to pointed, but not forming distinct process;
(1) extended in form of distinct ?ear-like? process
(CI = 0.500; RI = 0.875).
The posterodorsal corner of the opercle varies in
form across the Gymnotiformes, ranging most often
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 245
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
from being gently rounded [e.g. Sternarchorhamphus
(Albert, 2001: fig. 31b); Orthosternarchus tamandua
(Hilton et al., 2007: fig. 11)] to somewhat concave [e.g.
Electrophorus electricus (Albert et al., 2005: fig. 7)].
Species of Sternarchorhynchus, in contrast, have a
distally rounded ?ear-like? posterior extension of this
region of the opercle (state 1; Figs 9, 10). This process
is present solely in Sternarchella orthos amongst out-
groups in this study.
45. Association of posterodorsal corner of opercle
and supracleithrum: (0) rounded posterior extension
of opercle lying ventral of, or very slightly overlap-
ping, ventralmost portion of supracleithrum; (1)
rounded posterior extension of opercle extending over
ventralmost portion of supracleithrum (CI = 0.250;
RI = 0.625).
Sternarchorhynchus species other than S. axelrodi
and S. mormyrus share state 0 in which the opercle
demonstrates no or at most minimal overlap of the
ventral portion of the supracleithrum. State 0 is
present amongst outgroups in P. crypticus, Sternar-
chella orthos, and Sternarchorhamphus. Cleared and
stained specimens of S. mormyrus have an extensive
overlap of the ventralmost region of the supraclei-
thrum by the posterodorsal portion of the opercle.
Radiographs of specimens of its sister species, S.
axelrodi, revealed a comparable degree of overlap of
the two bones in that species (state 1). A similar
degree of extensive overlap (state 1) occurs in out-
groups in A. albifrons, A. cuchillo, A. rostratus, ?A.?
apurensis, Orthosternarchus tamandua, P. macros-
toma, and Sternarchogiton labiatus.
HYOID ARCH
The number of branchiostegal rays within the Gym-
notiformes ranges from two to five (Albert, 2001).
Variation in the number of elements involves differ-
ences in the number of rays associated with the
anterior and occasionally posterior ceratohyals. One
to three ceratohyals can attach to the ventral
margin of the anterior ceratohyal. The fourth
element has a variable area of attachment ranging
from the lateral surface of the posterior portion of
the anterior ceratohyal to the lateral surface of the
anterior region of the posterior ceratohyal. A fifth
ray, when present, attaches to the area of the joint
of the anterior and posterior ceratohyals (see Mago-
Leccia, 1978: fig. 13 for illustration of this arrange-
ment of five rays in Eigenmannia virescens) or to
the lateral surface of the posterior ceratohyal (see
de Santana & Nogueira, 2006: fig. 3 for illustration
of this condition in S. caboclo). Various authors have
used total ray counts to advance hypotheses of phy-
logenetic relationships (e.g. McAllister, 1968). Such
data, albeit informative at a general level, fail to
specify the presence versus absence of individual
rays. Phylogenetically useful information can be
better expressed in terms of individual elements; a
procedure we use herein.
46. Presence or absence of anterior most bran-
chiostegal ray attaching to ventral margin of anterior
ceratohyal: (0) absent; (1) present (CI = 0.500;
RI = 0.900).
One to three branchiostegal rays attach to the
ventral margin of the anterior ceratohyal; however, in
the absence of landmarks that allow us to homologize
elements unambiguously we only coded the number of
rays attaching to this bone when fewer than three
rays are present. Nonetheless, based on positional
information it appears that loss of branchiostegal
rays proceeds in an anterior posterior sequence that
leads us to cast the discussion within that framework.
Figure 13. Preopercle of A, Sternarchorhynchus severii, INPA 22898; and B, Sternarchorhynchus gnomus, INPA 25636;
showing differing forms of laterosensory canals in bone; left side, lateral view, anterior to left.
246 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
The first ray is absent in Orthosternarchus
tamandua, which also lacks the apparent second ray,
retaining only a single branchiostegal ray attaching
to the anterior ceratohyal (Hilton et al., 2007: fig. 13).
The first ray is missing in all species of Platyuroster-
narchus, the examined species of Apteronotus, and
Sternarchella orthos, Sternarchogiton labiatus, and
Sternarchorhamphus muelleri amongst the outgroup
taxa (state 0) and uniquely in S. caboclo within Ster-
narchorhynchus. Although this condition is autapo-
morphic for S. caboclo amongst osteologically
examined species of Sternarchorhynchus, we retained
it in the analysis because it may prove to be synapo-
morphic for a small clade once additional species of
the genus are examined osteologically.
47. Presence or absence of posteriormost bran-
chiostegal ray attaching either to lateral surface of
area of articulation of anterior and posterior cerato-
hyals or to anterior region of lateral surface of poste-
rior ceratohyal: (0) present; (1) absent (CI = 1.000;
RI = 1.000).
The posteriormost, typically larger, branchiostegal
ray in gymnotiforms attaches to the lateral surface of
the hyoid arch within the area delimited by the area
of joint between the anterior and posterior ceratohy-
als and the anterior region of the posterior ceratohyal.
Variation in the area of attachment forms a con-
tinuum across the examined taxa and we coded only
presence versus absence of the ray in this analysis.
This posteriormost branchiostegal ray is absent (state
1) in both Sternarchorhamphus muelleri and
Orthosternarchus tamandua (Hilton et al., 2007:
fig. 13), but present in Platyurosternarchus and Ster-
narchorhynchus (state 0). This ray is similarly
present in the examined species of Apteronotus and
Sternarchella orthos and Sternarchogiton labiatus.
Sternarchorhamphus muelleri and S. caboclo each
have four branchiostegal rays. That number is an
equivalent character state under previous coding
schemes focused on total numbers of rays rather than
presence versus absence of individual elements. The
reduced number of branchiostegal rays is achieved in
different fashions in the two taxa, being a conse-
quence of the loss of the anteriormost ray in S.
caboclo versus the absence of the posteriormost ray in
Sternarchorhamphus muelleri.
48. Relative size of first and second branchiostegal
rays: (0) rays of approximately same length; (1) first
ray approximately one-third length of second ray
(CI = 1.000; RI = 0.000).
Variation occurs in both the relative overall size
and length of the first and second branchiostegal
rays, but we focus in this character on the length of
the rays as this is a more readily quantifiable
attribute. With the single exception of S. inpai all
species of Sternarchorhynchus have the first and
second rays of more or less comparable lengths (state
0). In S. inpai the first ray is shortened to approxi-
mately one-third of the length of the second ray (state
1). Although this condition is autapomorphic for S.
inpai within Sternarchorhynchus in the present
analysis, we included it herein because it may define
a small clade within the genus in future studies that
incorporate species not examined osteologically in
this study. This character could not be coded in out-
groups to Sternarchorhynchus or in the genus for S.
caboclo, all of which lack the anteriormost ray.
49. Form of anterodorsal margin of third bran-
chiostegal ray: (0) smoothly convex; (1) with distinct
angular process (CI = 1.000; RI = 1.000).
The third branchiostegal ray has an overall
smoothly convex margin along its anterodorsal region
in both proximate outgroups to Sternarchorhynchus
[e.g. Orthosternarchus tamandua (Hilton et al., 2007:
fig. 13); the br1 of those authors] and the more dis-
tantly related apteronotids in the analysis (state 0).
Species of Sternarchorhynchus other than S. goeldii
and S. oxyrhynchus similarly share state 0. Both S.
goeldii and S. oxyrhynchus have the anterodorsal
portion of the third branchiostegal ray expanded into
a broadly angular pointed process (state 1).
50. Length of anterior branchiostegal ray attaching
to lateral surface of the anterior ceratohyal: (0) 1.5
times or less of distance from anterior limit of ventral
hypohyal to posterior limit of posterior ceratohyal; (1)
approximately three times distance from anterior
limit of ventral hypohyal to posterior limit of posterior
ceratohyal (CI = 1.000; RI = 1.000).
Species of Sternarchorhynchus and Platyurosterna-
rchus plus most examined outgroup apteronotids
have the anterior branchiostegal ray attaching to the
lateral surface of the anterior ceratohyal (the fourth
branchiostegal ray under the scheme of five total rays
detailed above) of a length equal to, or shorter than,
1.5 times the distance from anterior limit of the
ventral hypohyal to posterior limit of posterior cera-
tohyal. Fourth branchiostegal rays of comparable
relative lengths also occur in more distantly related
outgroups [e.g. Eigenmannia virescens (Mago-Leccia,
1978: fig. 15)]. Sternarchorhamphus muelleri and
Orthosternarchus tamandua have significantly longer
fourth rays of lengths approximately three or more
times the distance from the anterior limit of the
ventral hypohyal to the posterior limit of the posterior
ceratohyal (see Hilton et al., 2007: fig. 13 for
Orthosternarchus tamandua). Although the derived
elongation of the fourth branchiostegal ray is not
pertinent to the question of relationships within Ster-
narchorhynchus, we included the character to provide
structure to the outgroup phylogeny. A comparable
elongation of the second branchiostegal ray attaching
to the lateral surface of the posterior portion of the
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 247
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
hyoid arch (the fifth ray under the numbering scheme
herein) characterizes Sternarchorhamphus muelleri
and is apparently autapomorphic for that species.
51. Form of dorsal margin of proximate portion of
anterior branchiostegal ray attaching to lateral
surface of the anterior ceratohyal: (0) dorsally pointed
or rounded; (1) dorsally concave with angled margins
(CI = 1.000; RI = 0.000).
The dorsal portion of the anterior ray attaching to
the lateral surface of the anterior ceratohyal (the
fourth ray under the system described above) is either
dorsally rounded or pointed in outgroups to Sternar-
chorhynchus in the Apteronotidae. Sternarchorhyn-
chus caboclo, in contrast, has a strongly concave
dorsal margin to the ossification demarked by distinct
angled areas both anteriorly and posteriorly. This
character (state 1) is autapomorphic in the present
study, but was retained in the analysis as a potential
synapomorphy once additional species of Sternarcho-
rhynchus are examined osteologically.
52. Relative size of anterior portion of urohyal: (0)
relatively narrow and one-fifth or less of length of
main body of bone; (1) relatively wide and one-third or
more of length of main body of bone (CI = 0.333;
RI = 0.500).
In Orthosternarchus tamandua, Sternarchorham-
phus muelleri, S. goeldii, S. mormyrus, and S. oxy-
rhynchus, the anterior portion of the urohyal is
narrow relative to the overall size of the bone with its
transverse width approximately one-fifth or less of
the length of the main body (state 0; Fig. 14A).
Because of the reduction of the overall proportional
length of the urohyal, the anterior portion of the
urohyal is relatively wide relative to the overall size
of the bone in species of Sternarchorhynchus other
than S. goeldii, S. mormyrus, and S. oxyrhynchus.
This is reflected in a transverse width of the urohyal
that is approximately one-third or more of the length
of the main body of the ossification (state 1; Fig. 14B).
The urohyal is dramatically reduced in size and modi-
fied in form in the outgroup apteronotids other than
P. crypticus, P. macrostoma, and Sternarchella orthos
but, nonetheless, fits the definition of state 1 and was
coded accordingly. This character was not coded for
Sternarchogiton labiatus and the three examined
species of Apteronotus, all of which have highly modi-
fied urohyals. It was impossible to code S. axelrodi for
this character solely from radiographs of the types.
53. Form of anterior margin of urohyal: (0) straight
or slightly irregular, but without distinct medial
notch; (1) with distinct medial notch (CI = 0.200;
RI = 0.556).
The anterior margin of the urohyal is transversely
nearly straight or at most slightly irregular in
Orthosternarchus tamandua, P. crypticus, P. macros-
toma, Sternarchorhamphus muelleri, and most
Sternarchorhynchus species (state 0; Fig. 14A). Ster-
narchorhynchus chaoi, S. cramptoni, S. curumim, S.
hagedornae, S. higuchii, S. jaimei, S. mesensis, S.
montanus, S. roseni, and S. stewarti alternatively
have a distinct medial notch along the anterior
margin of the urohyal (state 1; Fig. 14B). This char-
acter could neither be coded for the other outgroup
apteronotids in which the urohyals are dramatically
Figure 14. Urohyal of A, Sternarchorhynchus oxyrhynchus, USNM 228787, and B, Sternarchorhynchus hagedornae,
USNM 391574; dorsal view, anterior at top.
248 C. D. DE SANTANA and R. P. VARI
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reduced in relative size and also modified in form, nor
for S. starksi, which had a deformed urohyal in the
single available cleared and stained specimen of the
species and S. axelrodi in the absence of cleaned and
stained specimens.
GILL ARCHES
54. Form of basihyal: (0) without lateral processes; (1)
with lateral processes (CI = 0.250; RI = 0.773).
The anteriormost component of the median ossifi-
cations of the lower half of the gill arches in all
examined apteronotids is an elongate ossification
identified by Hilton et al. (2007) as a fused basihyal
plus first basibranchial. Underlying this assumption
was the fact that the ossification occupies the area
encompassed by those elements in some other gym-
notiform families (e.g. Sternopygidae, see Mago-
Leccia, 1978: fig. 7) or by the ossified basihyal plus
cartilaginous first basibranchial in some taxa (e.g.
Eigenmannia, Mago-Leccia, 1978: fig. 17). In Sterna-
rchorhynchus the posterior limit of the anterior
element terminates between the anterior portions of
the first hypobranchials, the typical position for the
end of the basihyal and as such it appears that
basibranchial 1 is absent. We consequently identify
the elongate anterior ossification as the basihyal.
Apteronotus albifrons, A. cuchillo, A. rostratus, ?A.?
apurensis, Orthosternarchus tamandua (Hilton et al.,
2007: fig. 14), P. crypticus, P. macrostoma, Sternarch-
ella orthos, Sternarchogiton labiatus, and Sternar-
chorhamphus muelleri have this ossification ranging
from rod-like to slightly expanded transversely ante-
riorly, but without distinct lateral processes (state 0;
Fig. 15). Within Sternarchorhynchus an unelaborated
form of the basihyal (state 0) is restricted to S.
britskii, S. goeldii, S. higuchii, S. jaimei, S. oxyrhyn-
chus, and S. roseni. Other species of Sternarchorhyn-
chus have definite lateral processes along at least the
posterior half of the bone (state 1; Figs 16, 17).
55. Presence or absence of medial ridge on posterior
portion of dorsal surface of basihyal: (0) present; (1)
absent (CI = 1.000; RI = 1.000).
Various gymnotiforms have a medial ridge on the
dorsal surface of the posterior portion of the basihyal
(Triques, 1993: figs 12, 13). Such a process (state 0;
Figs 15?17) is present in all outgroups in this study
other than A. rostratus, Orthosternarchus tamandua,
and Sternarchella orthos and all species of Sternar-
chorhynchus other than S. inpai and S. montanus
(state 0). This ridge is absent in those two species
(state 1). This character could not be coded for in S.
axelrodi from radiographs.
56. Degree of separation between basihyal and
second basibranchial: (0) ossifications in close prox-
imity with posterior limit of basihyal extending pos-
teriorly nearly to transverse to posterior limit of
ossified portions of first hypobranchial; (1) ossifica-
tions distinctly separated with posterior limit of basi-
hyal extending posteriorly only to, or proximate to,
anterior region of ossified portion of first hypobran-
chial (CI = 1.000; RI = 1.000).
One notable variable amongst examined taxa
involves the degree of the extension posteriorly of the
basihyal. The condition typical for most apteronotids
including the outgroups to Sternarchorhynchus in this
study has a relatively small gap between the posterior
limit of the basihyal and the anterior margin of the
second basibranchial (state 0). This posterior position
of the terminus of the basihyal is reflected in the
location of the end of the ossification approximately at
the transverse to the posterior limit of the ossified
portion of the first hypobranchial (Hilton et al., 2007:
fig. 14 for an illustration of this condition in Orthoster-
narchus tamandua). The examined species of Sterna-
rchorhynchus, in contrast, have the posterior limit of
the basihyal situated between the anterior portions of
the contralateral first hypobranchials or anterior of
that position (state 1; Figs 15?17). This anterior posi-
tion of the terminus of the basihyal results in a major
gap between that ossification and the anterior limit of
the first hypobranchial.
57. Form of first hypobranchial: (0) triangular
overall with transverse dimension of ossified portion
slightly less than one-half length of that region; (1)
elongate with transverse dimension of ossified portion
approximately one-quarter to one-fifth length of that
region (CI = 1.000; RI = 1.000).
An overall triangular first hypobranchial (state 0;
Figs 15?17) is broadly distributed across all examined
taxa in the Apteronotidae and indeed elsewhere in the
Gymnotiformes (Mago-Leccia, 1978: fig. 7 for condi-
tion in a representative of the Sternopygidae). Within
the Apteronotidae, a distinct elongation of the first
hypobranchial occurs in both Orthosternarchus
tamandua and Sternarchorhamphus muelleri (state
1) amongst the taxa examined in this study. Although
not directly informative as to intrageneric relation-
ships within Sternarchorhynchus, we retained the
character in the analysis to provide structure within
the outgroup phylogeny.
58. Form of second basibranchial: (0) with
midlength constriction; (1) with lateral margins
running approximately in parallel (CI = 0.250;
RI = 0.700).
The majority of species of Sternarchorhynchus
along with all of the examined outgroups have the
second basibranchial constricted to a variable, but
nonetheless pronounced, degree along its midlength
(state 0). As a consequence, the element has a vari-
able hour-glass shape from dorsal view (Figs 15, 16).
In some outgroup taxa [e.g. Orthosternarchus
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 249
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
tamandua (Hilton et al., 2007: fig. 14)], the second
basibranchial is proportionally more elongate with a
relatively less pronounced but still obvious midlength
constriction. A subset of the species of Sternarcho-
rhynchus (S. chaoi, S. cramptoni, S. curvirostris, S.
hagedornae, S. jaimei, S. mesensis, S. mormyrus, S.
retzeri, S. severii, S. starksi, and S. stewarti) have a
bony plate extending laterally from the lateral
margins of the constricted portion of the main body of
the second basibranchial (state 1; Fig. 17). These
lateral extensions result in parallel lateral margins to
the second basibranchial from a dorsal view, albeit
with the constricted main body of the bone still
obvious; more so, in transmitted light (state 1). This
character could not be coded for S. axelrodi from
radiographs.
59. Form of anterior portion of second hypobran-
chial: (0) without distinct anterior extension from
main body; (1) with distinct anterior extension from
main body (CI = 1.000; RI = 1.000).
The second hypobranchial is a variably anteropos-
teriorly elongate bone amongst gymnotiforms, typi-
cally with an progressively tapering anterior region
that extends along the lateral margin of the second
basibranchial. Although outgroups to Sternarcho-
rhynchus along with S. goeldii and S. oxyrhynchus
have the anterior portion of this ossification some-
what pointed overall, the region is not developed into
a distinct narrow, often somewhat slightly medially
curving process (state 0; Fig. 15). All Sternarchorhyn-
chus species other than S. goeldii and S. oxyrhynchus
have the anterior portion of the second hypobranchial
Figure 15. Ventral portion of gills arches of Sternarchorhynchus goeldii, MCZ 46887; dorsal view, anterior at top; larger
stippling represents cartilage; small elements along anterior margins of ceratobranchials are highly reduced gill rakers.
250 C. D. DE SANTANA and R. P. VARI
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more attenuate, with this anterior extension
often slightly medially curving anteriorly (state 1;
Figs 16, 17).
60. Degree of development of medial portion of
second hypobranchial in adults: (0) with distinct
medial process extending ventral of second basibran-
chial and approaching contralateral second hypobran-
chial; (1) without distinct medial process and with
contralateral second hypobranchials separated by
second basibranchial (CI = 0.500; RI = 0.000).
The second hypobranchial in adults of nearly all
outgroups and all species of Sternarchorhynchus has
a medial extension directed towards its contralateral
partner in the area ventral of the second basibran-
chial. Amongst species for which we had a size range
of osteological preparations, the extension is less
developed in smaller individuals but ontogenetically
expands into a distinctly pointed process (state 0;
Figs 15, 17). Uniquely amongst the species examined
herein, S. caboclo and S. higuchii lack that medial
process of the second hypobranchial. They instead
have the contralateral ossifications completely sepa-
rated by the second basibranchial and the cartilage
that lies between that ossification and the third basi-
branchial (state 1; Fig. 16). This character could not
be coded for in S. axelrodi from radiographs.
61. Degree of constriction of medial portion of fourth
ceratobranchial: (0) constriction limited when
present; (1) constriction very distinct (CI = 1.000;
RI = 1.000).
When viewed from the dorsal view, the fourth cera-
tobranchial has nearly parallel lateral and medial
margins, or tapers slightly anteriorly in Orthosterna-
rchus tamandua (Hilton et al., 2007: fig. 14) and Ster-
narchorhamphus muelleri (state 0). Most examined
apteronotids and more distantly related gymnotiform
taxa either retain that morphology of the fourth cera-
tobranchial or have on occasion a lateral expansion of
the anterior portion of that ossification (e.g. Rhabdoli-
chops troschelii, Mago-Leccia, 1978: fig. 7). Species
Figure 16. Ventral portion of gills arches of Sternarchorhynchus caboclo, INPA 10594; dorsal view, anterior at top; larger
stippling represents cartilage; small elements along anterior margins of ceratobranchials are highly reduced gill rakers.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 251
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of Platyurosternarchus and Sternarchorhynchus,
however, have the anterior portion of the fourth cera-
tobranchial transversely constricted along the portion
of the bone somewhat distal of the region where the
ossified portion of the ceratobranchial merges into the
cartilage that caps the bone (state 1; Figs 15?17).
Such constriction of the fourth ceratobranchial is par-
ticularly pronounced in S. goeldii amongst species of
the genus represented by cleared and stained speci-
mens in this analysis. That condition may serve to
define a subunit of that genus once additional conge-
ners are examined osteologically.
62. Condition of fourth infrapharyngobranchial:
(0) totally cartilaginous; (1) ossified (CI = 1.000;
RI = 1.000).
The fourth infrapharyngobranchial is an anteropos-
teriorly elongate, posteriorly wider cartilaginous body
without ossification centres in both Orthosternarchus
tamandua (Hilton et al., 2007: fig. 14) and Sternar-
chorhamphus muelleri. An entirely cartilaginous
fourth infrapharyngobranchial is, furthermore,
general amongst other outgroups in the Apter-
onotidae (e.g. Adontosternarchus, Mago-Leccia et al.,
1985: fig. 5) and across the Gymnotiformes (e.g. the
sternopygids Eigenmannia and Rhabdolichops, Mago-
Leccia, 1978: figs 9, 17). It thus represents the primi-
tive condition across the Gymnotiformes (state 0). The
species of Sternarchorhynchus and Platyurosternar-
chus have a well-ossified fourth infrapharyngobran-
chial with an overall triangular, posteriorly widening
form (state 1; Fig. 18). The ossified portion of the
fourth infrapharyngobranchial is bordered anteriorly
by a small cartilage cap that contacts the cartilages of
the third epibranchial and third infrapharyngobran-
chial and terminates posteriorly along a transversely
elongate cartilage that broadly articulates with the
cartilage along the anterior margin of the fourth
epibranchial.
Figure 17. Ventral portion of gills arches of Sternarchorhynchus hagedornae, USNM 391574; dorsal view, anterior at top;
larger stippling represents cartilage; highly reduced gill rakers along anterior margins of ceratobranchials not illustrated.
252 C. D. DE SANTANA and R. P. VARI
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63. Degree of medial development of cartilage along
anterior margin of first epibranchial: (0) cartilage
extending along lateral, but not anterior margin of
cartilage at anterior of second infrapharyngobran-
chial; (1) cartilage expanded medially and extending
along all, or nearly all, of anterior margin of cartilage
along anterior margin of second infrapharyngobran-
chial (CI = 1.000; RI = 1.000).
Two primary conditions of the cartilages along the
anterior limits of the first epibranchial and the second
infrapharyngobranchial occur in Sternarchorhynchus
and its proximate outgroups. Orthosternarchus
tamandua (Hilton et al., 2007: fig. 14), Sternar-
chorhamphus muelleri, and other examined outgroup
apteronotids have a moderately sized cartilage along
the anterior margin of the first epibranchial. This
cartilage extends solely along the lateral margin of
the cartilage that caps the anterior limit of the ossi-
fied portion of the second infrapharyngobranchial. In
this configuration, the cartilage that anteriorly caps
the second infrapharyngobranchial retains a distinct
transversely exposed margin anteriorly (state 0).
Platyurosternarchus and Sternarchorhynchus have
the cartilage along the anterior portion of the first
epibranchial further expanded medially to a notable
degree. Therefore that cartilage overlaps not only the
lateral margin of the cartilage that caps the second
infrapharyngobranchial anteriorly, but extends to
varying degrees along the anterior margin of that
cartilage. As a consequence of this expansion of the
anterior cartilage of the first epibranchial, the carti-
lage at the anterior margin of the second infrapharyn-
gobranchial in Platyurosternarchus and Sternarch-
orhynchus lacks a broadly exposed margin anteriorly;
a derived condition (state 1; Fig. 1).
MYORHADOI
64. Form of ventral myorhadoi in central portions of
body: (0) central portion of myorhadoi without ventral
or dorsal elaborations; (1) central portion of myo-
rhadoi with ventral elaboration; (2) central portion of
myorhadoi with ventral and dorsal elaborations
(CI = 0.667; RI = 0.900).
Myorhadoi are the superficial series of the inter-
muscular bones that extend along the length of the
body in gymnotiforms and are variably present in
other fishes. The most common form of the large
series of these ossifications present across the Gym-
notiformes is a bony rod that progressively subdivides
distally at both ends with these terminal processes
extending further into the musculature. Such an
unelaborated bony rod along the central region of the
myorhadoi occurs in Orthosternarchus tamandua, P.
crypticus, P. macrostoma, Sternarchorhamphus muel-
leri, Sternarchella orthos, and Sternarchorhynchus
goeldii amongst the taxa in this study (state 0). All
other examined taxa have elaborations of the central
rod-like section of at least some of the myorhadoi;
Figure 18. Dorsal portion of gills arches of Sternarchorhynchus hagedornae, USNM 391574; right side, ventral view,
anterior at top; larger stippling represents cartilage.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 253
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with such extensions taking either of two forms
(states 1 or 2). Apteronotus albifrons, Sternarchogiton
labiatus, and all species of Sternarchorhynchus with
the exception of S. goeldii have an elaboration of the
portion of the central section of the portion of the
myorhadoi series located in the region of the body
approximately one-quarter the distance between the
rear of the abdominal cavity and the end of the anal
fin. The myorhadoi in that region have a relatively
long, curving, anteromedially directed extension
arising from the medial surface of the rod-like central
portion of the bone (states 1 and 2; Fig. 19A, B).
Sternarchorhynchus chaoi uniquely also has a shorter
anterodorsally orientated process arising from the
dorsal surface of the myorhadoi at a point approxi-
mately directly opposite to the base of the larger
anteroventral extension of the ossification (state 2;
Fig. 19B). This character could not be coded for S.
axelrodi solely based on radiographs of the types.
POSITION OF ANUS AND UROGENITAL PAPILLA
65. Ontogenetic shift in position of anus: (0) position of
anus relatively invariant in juveniles and adults with
anus situated posterior to vertical through eye in
adults; (1) position of anus distinctly ontogenetically
variable and shifting anteriorly with growth to loca-
tion anterior to vertical through eye in adults
(CI = 0.125; RI = 0.500).
Orthosternarchus tamandua, P. crypticus, P. mac-
rostoma, and Sternarchorhamphus muelleri lack an
ontogenetic anterior migration of the anus and uro-
genital papilla. Positional transitions were absent in
A. cuchillo, A. rostratus, Sternarchella orthos, and
Sternarchogiton labiatus amongst the more distant
outgroups in this analysis (state 0). Campos-da-Paz
(2000) remarked that the position of the anus (and
presumably the associated urogenital papilla) was
ontogenetically variable in a subset of the few species
of Sternarchorhynchus recognized at the time of his
analysis. Our analysis, involving as it does a signifi-
cantly greater number of now-recognized species,
documents that many Sternarchorhynchus species
demonstrate an ontogenetic shift anteriorly of the
anus and urogenital papilla (state 1; see listing of
species in Appendix 1). An anterior shift of the posi-
tion of the anus and urogenital papilla occurs in A.
albifrons and ?A.? apurensis? amongst the more dis-
tantly related apteronotids incorporated into the
analysis. This character was not coded for species of
Sternarchorhynchus for which available ontogenetic
series are too restricted to demonstrate potential
shifts in the position of the anus and urogenital
papilla.
NEUROCRANIUM
66. Presence or absence of scythe-shaped process along
lateral margin of ventral ethmoid: (0) absent; (1)
present (CI = 1.000; RI = 1.000).
The ventral ethmoid is fused to the anterior portion
of the vomer to form a compound ossification (see
discussion in Albert, 2001: 6?7). The lateral margin of
the ventral ethmoid lacks any pronounced scythe-
shaped elaborations in outgroups to Sternarchorhyn-
chus (state 0). Species of Sternarchorhynchus with
the exception of S. goeldii and S. oxyrhynchus (Fig. 2)
have contralateral, well-developed, posteriorly
directed, scythe-shaped processes arising from the
lateral margins of what is considered positionally to
be the ventral ethmoid (state 1; Fig. 3). Each scythe-
shaped process has a very small distal cartilage in
specimens of approximately 40 mm TL, but is com-
pletely ossified in adults and separate from any car-
tilage masses associated with the main body of the
vomer and/or parasphenoid.
The positionally somewhat similar expansions on
the lateral margin of the ventral ethmoid in examined
Figure 19. Myorhadoi from central portion of body of A, Sternarchorhynchus higuchii, INPA 20855; and B, Sternarcho-
rhynchus chaoi, INPA 20851; lateral view, anterior to left.
254 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
species of Apteronotus, along with Orthosternarchus
tamandua (Hilton et al., 2007: fig. 10c), Sternarchella
orthos, Sternarchogiton labiatus, and Sternar-
chorhamphus muelleri lack the scythe-shaped process
present in the vast majority of Sternarchorhynchus
species. These outgroups have, in contrast, postero-
laterally directed articular surfaces on the ventral
ethmoid that form the anterior limit of anteroposte-
riorly elongate cartilage bodies that extend along the
length of the vomer and sometimes parasphenoid. In
light of their significantly different overall morphol-
ogy and association with the vomerine cartilages,
those processes of the ventral ethmoid in these out-
groups are coded as state 0.
67. Relative length of the mesethmoid in adults:
(0) distance from tip of mesethmoid to vertical
through posteriormost limit of that bone less than,
to distinctly less than, distance from anteriormost
point on frontal to anterior margin of parietal; (1)
distance from tip of mesethmoid to vertical through
posteriormost limit of that bone equal to, or longer
than, distance from anteriormost point on frontal
to anterior margin of parietal (CI = 1.000; RI =
1.000).
One of the striking features of Sternarchorhyn-
chus is the pronounced development of the snout
into an elongate overall tubular structure. Elonga-
tion of the snout is achieved via diverse alterations
within the Apteronotidae (see Convergence in elon-
gation of snout under Discussion), but in Sternar-
chorhynchus the pronounced lengthening of the
mesethmoid is one of the major contributing factors
to the elongation of the dorsal portion of the neu-
rocranium. The mesethmoid in adults of that genus
spans approximately one-half the distance between
the tip of the snout and the anterior margin of the
opercle (state 1; Campos-da-Paz, 2000: fig. 6), with
the extension reflected in the relative length of the
mesethmoid versus the frontal. Juveniles of Sterna-
rchorhynchus have a proportionally much shorter
mesethmoid (compare Albert, 2001: fig. 17A, B) with
that ossification progressively increasing in
length ontogenetically. Although Orthosternarchus
tamandua amongst the proximate outgroups also
has an elongate overall head, the proportional elon-
gation of the mesethmoid is much less pronounced
in that species (Hilton et al., 2007: fig. 10) than in
Sternarchorhynchus. We also did not encounter dra-
matically elongated mesethmoids amongst outgroup
apteronotids in this study (state 0).
68. Presence or absence of lateral ethmoid: (0)
present; (1) absent (CI = 1.000; RI = 1.000).
A lack of the lateral ethmoid was ambiguously
polarized as a possible synapomorphy for Platyuro-
sternarchus plus Sternarchorhynchus by Albert &
Campos-da-Paz (1998) and Albert (2001; cited therein
as lateral ethmoid not ossified). Triques (2005) alter-
natively proposed that the lateral ethmoid was
present in both genera as is the case in the vast
majority of gymnotiforms, albeit sometimes repre-
sented as a cartilaginous element. The ambiguity in
the earlier studies as to the applicability of the
absence of a lateral ethmoid as a synapomorphy for
Platyurosternarchus plus Sternarchorhynchus was a
consequence of optimization resulting from the lack of
an ossified lateral ethmoid in the examined specimens
of Orthosternarchus tamandua. An ossified lateral
ethmoid was, however, reported as present in
Orthosternarchus tamandua by Hilton et al. (2007: 6,
fig. 10), albeit reduced in size and shifted anteriorly
relative to the typical condition in apteronotids. A
lateral ethmoid is similarly present in the cleared and
stained material of Orthosternarchus tamandua
examined herein. In light of the consequent recoding
of the condition in Orthosternarchus from lateral
ethmoid absent to present, the absence of the lateral
ethmoid in Platyurosternarchus and Sternarchorhyn-
chus (state 1) resolves in this study as an unambigu-
ous synapomorphy for those genera.
69. Degree of development of the ventral portion of
the orbitosphenoid: (0) well developed and extensive
along anteroposterior axis and extending anteriorly
along dorsal margin of parasphenoid; (1) relatively
narrow along anteroposterior axis and not extending
anteriorly along dorsal margin of parasphenoid
(CI = 1.000; RI = 1.000).
The orbitosphenoid extends ventrally from the
frontal to contact the dorsal margin of the parasphe-
noid in gymnotiforms and many other ostariophysans.
In the case of Orthosternarchus tamandua (Hilton
et al., 2007: fig. 10b), the species of Platyurosternar-
chus crypticus, and Sternarchorhamphus muelleri the
ventral portion of the orbitosphenoid proximate to the
parasphenoid is anteroposteriorly elongate with a
definite anterior extension along the dorsal surface of
the latter bone. This condition (state 0) occurs in the
examined outgroup species of Apteronotus and ?Apter-
onotus? along with Sternarchella orthos and Sternar-
chogiton labiatus. Sternarchorhynchus, in contrast,
has a more pillar-like form of the ventral portion of
the orbitosphenoid with either a limited anterior
extension where it contacts the parasphenoid or a
lack of such an elaboration. The orbitosphenoid in
Sternarchorhynchus similarly has at most a limited
posterior extension along the dorsal margin of the
parasphenoid (state 1; Fig. 20).
70. Form of posterior margin of orbitosphenoid: (0)
straight and abutting anterior margin of pterosphe-
noid along its entire length; (1) concave and contact-
ing pterosphenoid only at dorsal and ventral limits of
areas of contact of orbitosphenoid and pterosphenoid
(CI = 1.000; RI = 1.000).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 255
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Examined outgroups to Sternarchorhynchus and all
species of that genus other than S. axelrodi and S.
mormyrus have a continuous vertical cartilaginous
joint between the orbitosphenoid and pterosphenoid
[state 0; Fig. 20A; see also Hilton et al. (2007:
fig. 10b), for illustration of ventral portion of joint].
Cleared and stained and radiographed individuals of
S. mormyrus instead have a distinctly anteriorly
concave posterior margin of that portion of the orbito-
sphenoid. Contact between the orbitosphenoid and
the pterosphenoid is thus limited to separate areas of
articulation situated ventral and dorsal to concavity
(state 1; Fig. 20B). Although we lacked cleared and
stained specimens of S. axelrodi, the anterior concav-
ity of the posterior margin of the orbitosphenoid is
obvious in radiographs of the large specimens and the
species was coded as having state 1.
71. Form of anterior margin of pterosphenoid: (0)
straight and abutting anterior margin of orbitosphe-
noid along its entire length; (1) concave and contact-
ing orbitosphenoid only at dorsal and ventral limits of
areas of contact of pterosphenoid and orbitosphenoid
(CI = 1.000; RI = 1.000).
This character is associated with character 70. Out-
groups to Sternarchorhynchus and all examined
species of this genus other than S. axelrodi and S.
mormyrus have a straight, vertical anterior margin of
the orbitosphenoid (state 0; Fig. 20A). The cleared
and stained specimens of S. mormyrus in contrast
have a distinctly posteriorly concave anterior margin
of the pterosphenoid. That concavity in conjunction
with the adjoining concavity along the posterior
margin of the orbitosphenoid results in a large
foramen within the lateral region of the braincase.
Contact of the pterosphenoid with the orbitosphenoid
along the primitively continuous joint is as a conse-
quence reduced to two separate areas of articulation;
one situated dorsal to and the second ventral of the
foramen (state 1; Fig. 20B). An identical posterior
concavity of the anterior margin of the pterosphenoid
(state 1) is obvious in radiographs of large individuals
of A. axelrodi.
Apteronotus albifrons, A. cuchillo, and ?Apteronotus?
apurensis in the outgroups have a posteroventral
extension of the pterosphenoid that contacts the pos-
terior portion of the orbitosphenoid slightly above the
point where that bone articulates with the parasphe-
noid. This process and a small anterior concavity on
the orbitosphenoid jointly delimit a small transverse
foramen that at first consideration might be consid-
ered homologous with the foramen discussed in the
previous paragraph and under character 70 (see
Hilton & Cox-Fernandes, 2006: fig. 4, for a compa-
rable condition in A. bonapartii). The aperture in A.
albifrons, A. cuchillo, and ?A.? apurensis is positioned
distinctly ventral of the opening in S. axelrodi and S.
mormyrus and is formed by ventral extensions of the
orbitosphenoid and pterosphenoid rather than by the
main body of these bones such as is the case in S.
axelrodi and S. mormyrus. These apertures are
clearly nonhomologous with the foramen in the two
species of Sternarchorhynchus.
72. Anterior limit of anterior fontanel: (0) extending
anterior of anterior limit of orbitosphenoid; (1) falling
short of anterior limit of orbitosphenoid (CI = 0.500;
RI = 0.875).
Figure 20. Anterior portion of braincase and proximate bones of A, Sternarchorhynchus hagedornae, USNM 391574; and
B, Sternarchorhynchus mormyrus, USNM 306843; left side, lateral view, anterior to left; larger stippling represents
cartilage.
256 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Many ostariophysans including gymnotiforms have
a median frontoparietal fontanel that is typically
separated into anterior and posterior components by
the transversely aligned epiphyseal bar. Variation in
the extent of the anterior component of the fontanel
delimited by the frontals is pertinent to the groups of
interest. In both Platyurosternarchus and Sternar-
chorhamphus the frontal component of the fontanel
system is proportionally elongate with the anterior
limit of the aperture being situated anterior of the
orbitosphenoid. This condition (state 0) is also present
in the outgroups Apteronotus and ?Apteronotus? along
with Sternarchella orthos and Sternarchogiton labia-
tus. Orthosternarchus tamandua (Hilton et al., 2007:
fig. 10a) and Sternarchorhynchus species have less
extensive frontal fontanels that fall distinctly short of
the anterior limit of the orbitosphenoid (state 1).
PECTORAL GIRDLE
73. Presence or absence of mesocoracoid: (0) present;
(1) absent (CI = 1.000; RI = 1.000).
The mesocoracoid is a relatively small, vertically
elongate ossification running between the cleithrum
dorsally and the region of the joint between the cora-
coid and scapula ventrally. The possession of a meso-
coracoid is typical for gymnotiforms [e.g. species of
Gymnotus (Albert & Miller, 1995: fig. 5; Albert et al.,
2005: fig. 16)] and this ossification is present in
Orthosternarchus tamandua (Hilton et al., 2007:
fig. 18b) and Sternarchorhamphus muelleri. A meso-
coracoid is absent in Platyurosternarchus and Sterna-
rchorhynchus and amongst the outgroups of
immediate interest also in the species of Apteronotus
and ?Apteronotus? along with Sternarchella orthos and
Sternarchogiton labiatus (state 1).
74. Anterior extent of slender anteroventral process
of coracoid: (0) reaching to medial surface of clei-
thrum and terminating in small cartilage; (1) termi-
nating anteriorly distinctly short of medial surface of
cleithrum and with resultant gap filled by distinct
cartilage mass (CI = 0.500; RI = 0.000).
The coracoid extends anteriorly as an elongate,
typically anteriorly attenuating splint of bone
amongst gymnotiforms. This condition similarly
occurs in outgroups to Sternarchorhynchus examined
in this study (Hilton et al., 2007: fig. 18 for condition
in Orthosternarchus tamandua). Anteriorly, this
portion of the bone lies proximate to the medial
surface of the cleithrum and is capped by at most a
small cartilage body. This morphology of the coracoid
process (state 0) also characterizes all Sternarcho-
rhynchus species other than S. britskii and S. caboclo.
In these two species there is a distinct gap between
the anterior terminus of the anteroventral process
and the proximate portion of the cleithrum (state 1).
Filling that gap is an anteroposteriorly elongate car-
tilage much larger than the cartilage mass in that
position in congeners. This character could not be
coded for S. axelrodi based on radiographs of the
available specimens.
POSTCLEITHRA AND PROXIMATE INDEPENDENT
OSSIFICATIONS
Postcleithra are variably shaped, often flattened ossi-
fications embedded in the superficial tissues of the
body and positioned in part medial and more so
posterior to the pectoral girdle, in particular the clei-
thrum. These elements occur broadly across within
the Characiformes, albeit with zero to three postclei-
thra present in different families (comments by Vari,
1995: 26). Postcleithra are typically reduced to one
element in the Cypriniformes and lost in the Siluri-
formes (Fink & Fink, 1981). Species of Sternarcho-
rhynchus along with some other gymnotiforms have
been reported to possess one or more postcleithra, but
with these elements absent in some taxa within the
order [e.g. Sternopygus macrurus (Lundberg & Mago-
Leccia, 1986: fig. 8); Electrophorus electricus (Brous-
seau, 1976: 100)]. Nonetheless, positioning of
ossifications termed postcleithra by diverse authors
differs considerably across the Gymnotiformes; varia-
tion that raises questions as to the homology of some
of those bones.
Amongst immediate outgroups to Sternarchorhyn-
chus, we find that Orthosternarchus tamandua has a
single large, plate-like postcleithrum partially over-
lapped by the pectoral girdle (Hilton et al., 2007:
fig. 18). This element and the ossifications in the
species of Platyurosternarchus along with Sternar-
chorhamphus muelleri are positionally equivalent to
the first postcleithrum in the Characiformes [e.g.
Brycon meeki (Weitzman, 1962: fig. 18)] including the
basal families Distichodontidae and Citharinidae
(Vari, 1979: fig. 35). Ossifications located in this posi-
tion in Orthosternarchus and Sternarchorhamphus
are homologous with the first postcleithrum of other
orders of the Ostariophysi. A comparable first
postcleithrum is also present in Sternarchorhynchus,
with the bone followed by one or more additional
postcleithra in some species.
Diverse gymnotiforms have additional ossifications
of uncertain homology located in the region antero-
dorsal to the first postcleithrum. The apteronotid
genus Adontosternarchus bears three smaller, over-
lapping, longitudinally elongate ossifications in that
area (Mago-Leccia et al., 1985: fig. 6). A positionally
homologous anteroposteriorly elongate ossification
occurs in the basal gymnotiform genus Gymnotus.
More pertinently, a subset of the species of Sternar-
chorhynchus have an anteroposteriorly elongate bone
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 257
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
situated distinctly anterodorsal to the element that is
positionally homologous with the first postcleithrum
or the series of postcleithra in most groups in the
Characiformes. The simultaneous presence in many
gymnotiforms of one to three first postcleithra posi-
tionally homologous to those in many other ostari-
ophysans plus these additional ossifications makes it
clear that the more dorsally positioned bones in
various species of Sternarchorhynchus are not
postcleithra in terms of homology, notwithstanding
their locations posterior to the cleithrum.
This is likely to be the case with the bone or series of
dorsally positioned bones present in some outgroup
gymnotiforms.
For the purposes of the following discussion, we
utilize a positional concept for postcleithra. The
element partially overlapped by the posterior portion
of the cleithrum is herein coded as the first postclei-
thrum in keeping with its positional equivalence to
the ossification of that name in other ostariophysans
[e.g. Brycon meeki (Weitzman, 1962: fig. 18)]. Sequen-
tially posterior elements in that series are termed the
second and third postcleithra. In light of this conven-
tion, the ossification(s) situated anterodorsal to the
first postcleithrum in Adontosternarchus, Gymnotus,
and some species of Sternarchorhynchus coded under
character 75 are elements of uncertain homology.
75. Presence or absence of ossification located in
superficial tissues of body anterodorsal to first
postcleithrum: (0) absent; (1) present (CI = 0.167;
RI = 0.615).
An independent ossification situated posterior of
the cleithrum and anterodorsal to the first postclei-
thrum occurs in S. axelrodi, S. britskii, S. chaoi, S.
curvirostris, S. gnomus, S. goeldii, S. hagedornae, S.
inpai, S. montanus, S. mormyrus, S. oxyrhynchus, S.
severii, and S. starksi (state 1; Fig. 21). Amongst the
outgroup apteronotids examined in this study, this
ossification is present in ?A.? apurensis. No ossification
occurs in this region (state 0) in the remaining Ster-
narchorhynchus species or in A. albifrons, A. rostra-
tus, Orthosternarchus tamandua, P. crypticus, P.
macrostoma, Sternarchella orthos, Sternarchogiton
labiatus, and Sternarchorhamphus muelleri in the
outgroups.
Three ossifications identified as postcleithra were
illustrated in the same general region by Mago-Leccia
et al. (1985: fig. 8) in the apteronotid Adontosternar-
chus devenanzii. These bones differ in orientation and
form from the ossification present in that area in
some Sternarchorhynchus species. This makes it dif-
ficult to evaluate the possible homology between the
elements in Adontosternarchus and the single bone
present in some species of Sternarchorhynchus. As
discussed above, in light of positional differences, we
do not equate these ossifications with the postcleithra
found in various gymnotiforms and characiforms.
Furthermore, Adontosternarchus and Sternarcho-
rhynchus are not close relatives (Albert, 2001) and
the ossifications situated in the superficial tissues
anterodorsal to the first postcleithrum even if homolo-
gous in those genera, nonetheless, demonstrate a
homoplastic distribution.
76. Form of ossification located anterodorsal to first
postcleithrum: (0) rounded or ovoid; (1) elongate
(CI = 0.250; RI = 0.400).
Figure 21. Posterior portion of cleithrum, postcleithra, and independent ossification in A, Sternarchorhynchus hagedor-
nae, USNM 391574; and B, Sternarchorhynchus mormyrus, USNM 306843; left side, lateral view, anterior to left.
258 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
When present, the independent ossification
reported under character 75 has either of two forms
in Sternarchorhynchus and other examined apter-
onotids. A rounded, ovoid, or slightly irregularly rect-
angular form of the bone (state 0; Fig. 21A) occurs in
S. chaoi, S. gnomus, S. hagedornae, S. inpai, S.
montanus, S. severii, and S. starksi and in the out-
group in ?A.? apurensis. In contrast, an anterodorsally
distinctly elongate form of the ossification (state 1;
Fig. 21B) is present in S. axelrodi, S. britskii, S.
curvirostris, S. goeldii, S. mormyrus, and S. oxyrhyn-
chus. This ossification is absent and could not be
coded in the remaining Sternarchorhynchus species
examined osteologically along with A. albifrons, A.
rostratus, Orthosternarchus tamandua, P. crypticus,
P. macrostoma, Sternarchella orthos, Sternarchogiton
labiatus, and Sternarchorhamphus muelleri in the
outgroups.
77. Number of postcleithra: (0) one postcleithrum;
(1) two postcleithra; (2) three postcleithra (CI = 0.400;
RI = 0.400).
A single postcleithrum (state 0), the first postclei-
thrum under the numbering system discussed
above, is the only element of that series present in
Orthosternarchus tamandua (Hilton et al., 2007:
fig. 18) and Sternarchorhamphus muelleri. A second
postcleithrum located posterior to the first postclei-
thrum is present in Platyurosternarchus and Ster-
narchorhynchus for a total of at least two
postcleithra in these genera [states 1 (Fig. 20A, B)
and 2]. Outgroups with a second postcleithra are A.
cuchillo, ?A.? apurensis, and Sternarchogiton orthos.
Sternarchorhynchus curvirostris, S. inpai, S.
mendesi, S. mesensis, and S. roseni have a third
postcleithrum (state 2).
78. Form of second postcleithrum: (0) rounded or
slightly longitudinally ovoid; (1) horizontally elongate
(CI = 0.250; RI = 0.500).
The second postcleithrum is located immediately
posterior of the first element in that series
that is overlapped, in turn, by the posterior
margin of the cleithrum. Two morphologies
of the second postcleithrum occur within Platyuro-
sternarchus, Sternarchorhynchus, and the other
examined apteronotids bearing that ossification. In
P. crypticus, P. macrostoma, S. goeldii, S. mormyrus,
and S. oxyrhynchus the bone is horizontally elongate
(state 1; Fig. 21B), whereas in all other species of
Sternarchorhynchus the ossification is either round
or only slightly longitudinally ovoid (state 0;
Fig. 21A). An elongate morphology of the second
postcleithrum (state 1) also occurs in A. cuchillo
and ?A.? apurensis. This character could not be
coded for outgroups that lack a second postclei-
thrum or for S. axelrodi based on radiographs of the
types.
WEBERIAN COMPLEX
79. Form of intercalarium: (0) transversely elongate;
(1) rhomboidal or rectangular; (2) medially tapering
and triangular overall (CI = 0.667; RI = 0.500).
The intercalarium is one of the set of ossicles within
the pars auditum of the Weberian apparatus. These
ossicles, along with associated soft tissues, the swim-
bladder, and components of the neurocranium are
directly involved in the detection of sound in the
water column. The intercalarium in gymnotiforms is
a relatively small ossification located within the inter-
osseus ligament that extends anterodorsally from the
anterior tip of the tripus and then continues anteri-
orly to the scaphium (De La Hoz & Chardon, 1984:
fig. 24, for illustration of arrangement in Sternopygus
macrurus). Three morphologies of this ossification
occur in Platyurosternarchus, Sternarchorhynchus,
and the examined outgroup apteronotids. State 0, a
transversely elongate form of the intercalarium, is
limited to P. crypticus and P. macrostoma amongst
examined taxa. In Sternarchorhynchus species with
the exception of S. mesensis and S. starksi the inter-
calarium is overall rectangular or posteriorly nar-
rower medially, but, nonetheless, extends a distinct
distance medially along the axis of the interosseus
ligament (state 1; Fig. 22A). A rhomboidal form of the
ossification occurs in A. cuchillo, ?A.? apurensis,
Orthosternarchus tamandua, and Sternarchorham-
phus muelleri. A rectangular morphology of the inter-
calarium is present in A. albifrons, A. rostratus,
Sternarchella orthos, and Sternarchogiton labiatus
(state 1). In S. mesensis and S. starksi the bone
distinctly tapers medially to a point and has an
overall triangular form when examined from a dorsal
view (state 2; Fig. 22B). It was impossible to code this
character for S. axelrodi from radiographs of the
types.
80. Form of tripus: (0) progressively narrowing
away from area of attachment to the centrum of the
third vertebra and with relatively narrow distal tip;
(1) not distinctly narrowing distally and relatively
wide for distal half of bone (CI = 1.000; RI = 0.000).
The tripus, another of the set of ossicles within the
pars auditum of the Weberian apparatus, progres-
sively attenuates as it extends distally from its area
of attachment on the centrum of the third vertebra
both in outgroups to Sternarchorhynchus and most
members of that genus (De La Hoz & Chardon, 1984:
fig. 24, for illustration of comparable arrangement in
Sternopygus macrurus). The distal portion of the
tripus has an abrupt change in angle towards the
midline in Platyurosternarchus and is more gradually
angled in that direction in most species of Sternar-
chorhynchus (state 0; Fig. 22A). Regardless of the
details of the morphology of that region of the tripus,
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 259
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
the distal half of the ossification becomes progres-
sively narrower and is quite narrow distally relative
to the more anterior portions of the bone. This con-
dition is also the case in the examined outgroups to
the genus. In S. mesensis the distal half of the tripus
is of approximately constant width and forms a wide
overall process with a more obtuse distal tip. The
width of the posterior portion of the tripus is approxi-
mately one-half that of the anterior region of the bone
(state 1; Fig. 22B). Although the character is autapo-
morphic for S. mesensis amongst the species of Ster-
narchorhynchus included in this study, it may serve
as a synapomorphy for a small subunit of the genus
once additional species of the genus are included in
the analysis. It was impossible to code this character
for S. axelrodi based on radiographs of the types.
CAUDAL FIN
81. Ossification of hypural plate: (0) plate ossified; (1)
plate cartilaginous (CI = 1.000; RI = 1.000).
An ossified hypural plate is common to both Ster-
narchorhynchus and Platyurosternarchus, whereas
the plate is cartilaginous in Orthosternarchus
tamandua (Hilton et al., 2007: fig. 17a) and Sternar-
chorhamphus muelleri [state 1; note: the specimen
illustrated by Fink & Fink (1981) as Sternarchorham-
phus with an ossified hypural plate is rather P. cryp-
ticus]. The plate is also ossified in other examined
outgroup apteronotids, although with some specimens
of A. rostratus having only a slightly developed ossi-
fication node in the central portion of what appears to
be an otherwise cartilaginous plate. Other specimens
of this species, in contrast, have a well-ossified
hypural plate, with A. rostratus coded as having that
condition (state 0).
SCALATION
82. Scales along mid-dorsal region of body anterior to
origin of electroreceptive filament: (0) present; (1)
reduced to some extent and sometimes largely absent
(CI = 0.250; RI = 0.750).
The mid-dorsal region of the body in most gymno-
tiforms is scaled, albeit with scales sometimes sparse
and hidden to varying degrees by the overlying skin
(state 0). This condition is present amongst the out-
groups in A. albifrons, A. cuchillo, and A. rostratus.
Most examined species of Sternarchorhynchus simi-
larly have the mid-dorsal region of the body anterior
Figure 22. Tripus, intercalarium, and associated portions of interosseus ligament of A, Sternarchorhynchus oxyrhynchus,
USNM 228787; and B, Sternarchorhynchus mesensis, MNRJ 13216; left side, dorsal view, anterior at top; dashed bands
indicate ligament.
260 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
of the origin of the electroreceptive organ scaled (state
0). Scales are lacking in variably extensive portions of
the mid-dorsal areas anterior to the origin of the
electroreceptive that region of the body in ?A.? apuren-
sis, Orthosternarchus tamandua, P. crypticus, P. mac-
rostoma, Sternarchella orthos, Sternarchogiton
labiatus, Sternarchorhamphus muelleri, S. axelrodi,
S. chaoi, S. goeldii, S. jaimei, S. mormyrus, and S.
oxyrhynchus (state 1).
83. Degree of reduction of scaling along mid-dorsal
portion of body anterior to origin of electroreceptive
filament: (0) scales absent along entire mid-dorsal
region to origin of electroreceptive filament; (1) scales
absent along mid-dorsal region only to region approxi-
mately at vertical through posterior margin of pecto-
ral fin (CI = 1.000; RI = 1.000).
Sternarchorhynchus species and members of the
outgroup with reductions in the scales along the mid-
dorsal region of the body demonstrate two different
degrees of that reduction. In S. axelrodi, S. goeldii, S.
mormyrus, and S. oxyrhynchus along with the out-
groups ?A.? apurensis, Orthosternarchus tamandua, P.
crypticus, P. macrostoma, Sternarchella orthos, Ster-
narchogiton labiatus, and Sternarchorhamphus muel-
leri the scales are absent along the entire mid-dorsal
region to the origin of the electroreceptive filament
(state 0). Sternarchorhynchus chaoi and S. jaimei
have less extensive reduction of the scale covering in
the mid-dorsal region of the body, with the scales
missing from the rear of the head approximately to
the vertical through the posterior margin of the pec-
toral fin (state 1). This character was not coded for
species that retain scales anterior by some degree to
the electroreceptive filament origin, whether in the
form of complete or sparse scaling.
84. Degree of development of mid-dorsal scales when
present along mid-dorsal portion of body anterior to
origin of electroreceptive filament: (0) scales well
developed and obvious; (1) scales sparse and covered
to different degrees by skin (CI = 0.500; RI = 0.667).
Species of Sternarchorhynchus that retain scales
along the mid-dorsal region anterior of the origin of
the electroreceptive filament vary in the degree to
which the scales are present and readily obvious
externally. Most species of the genus with a scaled
mid-dorsal region (all species other than S. hagedor-
nae, S. higuchii, S. mendesi, and S. roseni) have very
obvious scales in that region (state 0). State 0 is also
present in the outgroups in A. albifrons, A. cuchillo,
and A. rostratus. In S. hagedornae, S. higuchii, S.
mendesi, and S. roseni the mid-dorsal scales in the
region anterior to the electroreceptive region,
although present, are somewhat sparse and covered
to varying degrees by skin (state 1). Given the pres-
ence of scales along at least part of the mid-dorsal
area, this condition differs from the lack of scales in
that region in characters 82 and 83. This character
could not be coded for species lacking scales along the
mid-dorsal region anterior to the electroreceptive fila-
ment (characters 82, 83).
COLORATION
85. Presence or absence of narrow, mid-dorsal, lightly
coloured stripe on head: (0) mid-dorsal portion of head
with pigmentation comparable to that of laterally
adjoining regions or with pigmentation darker; (1)
mid-dorsal region of head with narrow, mid-dorsal,
lightly coloured stripe (CI = 0.333; RI = 0.833).
Immediate outgroups to Sternarchorhynchus
(Orthosternarchus, Platyurosternarchus, Sternar-
chorhamphus) along with Sternarchella orthos and
Sternarchogiton labiatus amongst more distant out-
groups all have the coloration of the mid-dorsal por-
tions of the head comparable to, or darker than, that
of the laterally adjoining regions of the head (state 0).
The majority of species of Sternarchorhynchus (state
1; Appendix 1), in contrast, have a narrow to very
narrow, mid-dorsal, distinctly more lightly coloured
stripe extending from, or proximate to, the tip of the
snout posteriorly to at least the interorbital region
and sometimes further posteriorly on the head (state
1). Some species with such a stripe have that pigmen-
tation pattern continuous with a comparable mid-
dorsal stripe along the body that extends to varying
degrees posteriorly towards, or sometimes beyond,
the origin of the electroreceptive filament. Amongst
the outgroups, such a mid-dorsal lightly coloured
stripe (state 1) is also present in A. albifrons, A.
cuchillo, and A. rostratus. Two species of Sternarcho-
rhynchus, S. britskii and S. mesensis, were reported
to have only an indistinct mid-dorsal stripe on the
snout in certain individuals (Campos-da-Paz, 2000),
but these species are coded as state 1 in light of the
presence of the stripe to some degree in the material
of these species examined in this study.
86. Presence or absence of narrow, lightly coloured
stripe on lateral surface of snout: (0) lateral surface of
snout with pigmentation comparable to that of adjoin-
ing regions or with irregular marbling; (1) lateral
surface of snout with distinct, more lightly coloured
band (CI = 0.333; RI = 0.857).
All examined apteronotid outgroups to Sternarcho-
rhynchus have uniform coloration of the lateral
surface of the snout or when the pigmentation in this
region is non-uniform it is marbled or otherwise
irregular (state 0). Such uniform pigmentation along
the snout is common to S. curvirostris, S. goeldii, S.
oxyrhynchus, S. roseni, and S. starksi. In contrast, S.
axelrodi, S. britskii, S. caboclo, S. chaoi, S. cramptoni,
S. curumim, S. gnomus, S. hagedornae, S. higuchii,
S. inpai, S. jaimei, S. mareikeae, S. mormyrus,
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 261
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
S. mendesi, S. mesensis, S. montanus, S. retzeri,
S. severii, and S. stewarti have a distinct, more lightly
coloured band extending along the lateral surface of
the snout in the region anterior to the eye and some-
times continuing nearly to the tip of the snout (state
1).
87. Presence or absence of dark coloration along
basal portion of anal fin: (0) fin hyaline to slightly
dusky overall, but lacking distinct band of dark pig-
mentation basally; (1) fin hyaline to slightly dusky
overall, with distinct band of dark pigmentation
basally (CI = 1.000; RI = 0.000).
Anal fin coloration in Sternarchorhynchus ranges
from hyaline to somewhat dusky overall, but most
species of the genus along with all outgroups in this
analysis lack a band of distinctly darker pigmentation
extending along the basal portion of the fin (state 0).
Such a band of dark, basal pigmentation on the anal
fin is limited to S. curvirostris amongst species of the
genus (state 1). Although autapomorphic for this
species in this analysis, we included this feature
because future analyses may find it to be more
broadly distributed with the inclusion of additional
species.
Triques (2005) proposed that dark coloration of the
caudal peduncle and adjoining regions was synapo-
morphic for a clade formed by Platyurosternarchus,
Sternarchorhynchus, and Ubidia. This pigmentation
is rare amongst the species of Sternarchorhynchus. As
discussed under the framework for outgroup compari-
sons, the caudal pigmentation of Platyurosternarchus
and Ubidia differs in various details with the colora-
tion of the latter genus more similar to that of a
subunit of Apteronotus.
88. Presence or absence of dark coloration along
distal portions of anal fin: (0) fin hyaline to slightly
dusky overall, but lacking distinct band of dark pig-
mentation along distal portion of fin; (1) fin hyaline to
slightly dusky overall, and with distinct band of dark
pigmentation distally (CI = 0.167; RI = 0.375).
Anal fin coloration in preservative in Sternarcho-
rhynchus ranges from hyaline to somewhat dusky
overall, but most species in the genus along with A.
albifrons, A. cuchillo, A. rostratus, Orthosternarchus
tamandua, P. crypticus, and P. macrostoma lack a
band of distinctly darker pigmentation along the
distal margin of the anal fin (state 0). ?Apteronotus?
apurensis and Sternarchorhamphus muelleri in the
outgroups together with S. axelrodi, S. cramptoni, S.
goeldii, S. montanus, S. mormyrus, S. oxyrhynchus,
and S. retzeri have instead a distinct band of dark
pigmentation along the distal portions of the anal fin
(state 1). This darkly pigmented band covers one-fifth
to one-half of the distal portions of much of the
anterior and middle anal-fin rays and in some
instances all, or nearly all, of the posterior rays of the
fin. The dark coloration on the anal fin in the species
of Platyurosternarchus is limited to the posteriormost
portion of the fin and extends to the base of the
involved fin rays (de Santana & Vari, 2009); a very
different and thus nonhomologous pattern.
Sternarchorhynchus roseni demonstrates variation
in the presence or absence of dark pigmentation on
the anal fin, with the presence of such coloration
correlated with the possession in mature males of an
anteriorly expanded dentary with enlarged dentition.
This correlation raises the possibility that the pres-
ence of dark pigmentation is a seasonal, sexually
dimorphic feature for males and we consequently code
S. roseni as unknown for this character.
DISCUSSION
PHYLOGENETIC RECONSTRUCTION AND KEY
INNOVATIONS
Twenty-four nodes were resolved in the phylogenetic
analysis for, and within, the clade formed by
Platyurosternarchus plus Sternarchorhynchus (clade
numbering in Fig. 23). Reconstructed relationships
amongst the outgroup taxa in this study beyond the
hypothesis of a sister-group relationship between
Platyurosternarchus and Sternarchorhynchus should
not be viewed as well-supported phylogenetic hypoth-
eses and support for those portions of the phylogeny
is not detailed on the cladogram. The potential uncer-
tainty in outgroup relationships is derivative of
several limitations with the underlying data. Taxon
sampling amongst apteronotids outside of Platyuro-
sternarchus and Sternarchorhynchus was of necessity
sparser than within those genera that were the
subject of in-depth analyses by, respectively, de
Santana & Vari (2009) and herein. Notwithstanding
the fact that some characters were incorporated into
the analysis in order to provide structure to the
outgroup phylogeny, we did not search for new char-
acters informative about relationships amongst and
within the outgroup taxa incorporated into this study.
Characters previously reported in the literature as
informative about relationships within the Apter-
onotidae were typically excluded from this analysis
unless germane to the core questions phylogenetic
addressed in the study. The evidence for the sister-
group relationship between Orthosternarchus
tamandua and Sternarchorhamphus muelleri arrived
at herein does, however, conform with the hypotheses
advanced by Campos-da-Paz (1995) and various sub-
sequent authors.
The results strongly support the hypothesis of a
sister-group relationship between Platyurosternar-
chus and Sternarchorhynchus advanced by authors
starting with Albert & Campos-da-Paz (1998), albeit
262 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Figure 23. Strict consensus of eight most parsimonious trees generated in PAUP*, length = 193, consistency index
(CI) = 0.477, and retention index (RI) = 0.814, with all branches of zero maximum length collapsed and all characters
unordered. Each of the most parsimonious trees has length = 190, CI = 0.484, and RI = 0.820. Synapomorphies only
mapped for and within clade consisting of Platyurosternarchus and Sternarchorhynchus.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 263
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
with some differences in the underlying evidence (see
Synapomorphy list in Appendix 2 for details). Several
of the synapomorphies common to those two genera
are of particular note in being unambiguous modifi-
cations unusual not only within the Apteronotidae but
in some instances across the Gymnotiformes. Striking
from that perspective are the restructuring of the
posterior portion of the anguloarticular (character
17), the very distinct constriction of the medial
portion of the fourth ceratobranchial (character 61),
the well-ossified fourth infrapharyngobranchial (char-
acter 62), and the absence of the lateral ethmoid
(character 68). The results of this study and those of
de Santana & Vari (2009) also support the hypothesis
of the monophyly of Platyurosternarchus. A number of
the derived modifications at the level of Platyuroster-
narchus similarly involve the jaws and dentition.
These include the absence of teeth on premaxilla
(character 4), and the attachment of teeth to the
exterior surface of the dentary (character 20).
Of particular note within the clade formed by
Platyurosternarchus plus Sternarchorhynchus are the
extensive series of synapomorphies for Sternarcho-
rhynchus (Synapomorphy list in Appendix 2 for
details), with a high percentage (77%) of the 27 char-
acters informative as to the monophyly of Sternarcho-
rhynchus being unambiguous characters uniquely
derived at the level of the genus. These numerous
synapomorphies are by far the greatest number of
such features defining any genus within the Gymno-
tiformes (Albert, 2001, for other genera). Seven of the
27 synapomorphies for Sternarchorhynchus involve
restructurings of components of the jaws (character 5,
the form of the maxilla; character 9, the reduction of
the coronomeckelian bone; character 10, the reduction
of Meckel?s cartilage; character 11, the relative devel-
opment of the posterodorsal and posteroventral pro-
cesses of the dentary; character 12, the form of the
posteroventral process of the dentary; character 15,
the position on the lower jaw of the articular facet
contacting the quadrate; and character 16, the form of
the anterior portion of the anguloarticular). Seven
additional synapomorphies for Sternarchorhynchus
involve alterations of the suspensorium so that it can
be accommodated in the vertically constricted tubular
snout or are correlated with the remodelling of com-
ponents of the jaws (character 21, the reduction of the
anterior portion of the palatoquadrate cartilage; char-
acter 22, the shift ventrally in the relative position of
the endopterygoid; character 23, the reduction of the
anterior portion of the endopterygoid; character 24,
the reduction of the posterior portion of the endop-
terygoid and the closer association or fusion of that
ossification with the quadrate; character 28, the loss
of the dorsal portion of the quadrate; character 35,
the shift of the posterior limit of the posteroventral
portion of the quadrate; and character 38, the hori-
zontal elongation of the metapterygoid). Except for
character 11, none of these modifications was mani-
fested within the examined outgroups. Of the restruc-
turings of the neurocranium at this level of the
phylogeny, one synapomorphy (character 67, the
increase in the proportional distance from the tip of
the mesethmoid to the vertical through the posteri-
ormost limit of that bone) is clearly correlated with
the dramatic proportional elongation of the snout
characteristic of Sternarchorhynchus. These 15 modi-
fications of the jaws, suspensorium, and anterior
portion of the neurocranium all correlate with the
distinctive form of the jaws, snout, and associated soft
tissue systems that permit grasp-suction or suction
assisted by mechanical grasping in the species of
Sternarchorhynchus (comments under Adaptive
radiation in the next section).
Figure 24. Two alternative topologies of species within clade 24 with characters mapped under ACCTRAN optimization.
264 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
The synapomorphies for Sternarchorhynchus that
are heavily weighed towards modifications of the
jaws, suspensorium, anterior portion of the neurocra-
nium, and associated systems are recognized herein
as key innovations [i.e. special set of characteristics ?
sensu Liem (1973), Lauder (1981)] within a compara-
tive phylogenetic framework as proposed by Stiassny
& Jensen (1987). The concept of key innovation has
been used in diverse fashions, usually focusing on
attributes purported to account for the success for a
lineage in any of several ways, including species rich-
ness and morphological diversity. Herein we focus on
species richness resultant from morphological modi-
fications, specifically asymmetrical divergence in
species numbers between Platyurosternarchus and
Sternarchorhynchus following the criterion of Guyer
& Slowinski (1993).
That being said, there remains controversy on the
issue of whether key innovations serve as triggers of
diversification (e.g. Cracraft, 1990) and it is difficult
to test for such features (Hodges, 1997). One diffi-
culty with the discussion of key innovations is the
lack of a standard to assess diversity and species
richness (Jensen, 1990). Jensen (1990) reviewed the
process for historical testing for key innovations.
Historical testing uses convergence to search for
independent corroboration of hypotheses relating
evolutionary novelties with phylogenetic patterns
(Jensen, 1990). That author proposed that historical
testing must be a two-step process. The first step
involves a comparison of the species diversity of a
taxon exhibiting a proposed key innovation or inno-
vations with that of its sister group. Following that
is the comparison of sister groups in independent
lineages in which an identical novelty has evolved.
This ascertains whether comparable disparate pat-
terns of species richness occur in each of the inde-
pendent lineages.
In the present study, the first step involves a com-
parison of species diversity of Sternarchorhynchus
versus Platyurosternarchus. The second step is a com-
parison of the species richness in the two genera of
freshwater fishes in which grasp-suction feeding has
been reported (Sternarchorhynchus and the African
electric fish genus Campylomormyrus), versus their
sister taxa (Platyurosternarchus and Gnathonemus,
respectively) neither of which demonstrates that
feeding system (for further information on the species
diversity and relationships amongst Mormyriformes
genera see Moller, 1995; Sullivan, Lavou? & Hopkins,
2000; Feulner et al., 2007).
In both the South American and African lineages,
the groups in which grasp-suction feed mode has
evolved (Sternarchorhynchus with 32 species and
Campylomormyrus with 14-plus species) are more
diverse than are sister taxa that do not demonstrate
that mode of feeding (Platyurosternarchus with two
species and Gnathonemus with five species, respec-
tively; for further details see Adaptive radiation and
Convergence in elongation of snout sections). Campy-
lomormyrus is forecast to be even more diverse than
presently recognized (Feulner et al., 2007). This con-
sistent pattern of relative species richness between
Sternarchorhynchus and Campylomormyrus versus
their sister groups satisfies the second criterion
advanced by Jensen (1990). We thus propose that the
various synapomorphies for Sternarchorhynchus
noted above, in particular the restructuring of com-
ponents of the jaws, suspensorium, and anterior
portion of the neurocranium that permit the grasp-
suction feeding as likely key innovations linked to the
adaptive radiation within that genus.
Looking at the distribution of synapomorphies of
and within Sternarchorhynchus, particularly of
uniquely derived features, we find a remarkable
asymmetry in the occurrence of these attributes
across the phylogeny of the genus (Fig. 23). Clades 1
to 7 in Sternarchorhynchus involve 39 such synapo-
morphies contrary to the presence of only one
uniquely derived synapomorphy across clades 8 to 24.
The pronounced loading of these characters at the
basal levels within the clade formed by Platyuroster-
narchus and Sternarchorhynchus correlates with a
number of novel modifications of various body
systems at these levels. These potential key innova-
tions particularly load at the level of clade 3 where
they involve the synapomorphies for the species of
Sternarchorhynchus associated with capture and
initial processing of prey items. Such loading of major
modifications applies, albeit to a lesser extent, at the
level of other basal clades within that genus (clades 4
to 7), all of which are defined by multiple synapomor-
phies. With few exceptions, clades 8 to 24 are instead
defined by single homoplastically distributed synapo-
morphies that involve aspects of the feeding system.
The underlying cause of this pattern of synapomorphy
distribution is impossible to discern from the morpho-
logical data, nor is relative timing of cladogenesis
determinable in the absence of any benchmark vicari-
ance events that provide a temporal context to the
phylogeny. One explanation involves rapid speciation
at less inclusive levels within the phylogeny of the
genus. Such a clustering of modifications at the basal
clades is congruent with expectations under the
hypothesis of adaptive radiation (Foote, 1997;
Schluter et al., 1997; Schluter, 2000; also comments
under Adaptive radiation below).
Having arrived at a series of innovations that
permit the very unusual, albeit clearly highly func-
tional, grasp-suction feeding mode at the level of
Sternarchorhynchus (clade 3), there followed less dra-
matic modifications of the jaws, suspensorium, and
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 265
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
gill arches at basal levels within the genus. Clade 4,
consisting of S. goeldii and S. oxyrhynchus, is char-
acterized by several unique distinctive modifications
of these body systems (character 1, the mouth length;
character 6, the reduction of the anterior portion of
the maxilla; character 8, the presence of a fleshy,
dorsally directed pad at the anterior margin of the
dentary; character 25, the fusion of the quadrate and
endopterygoid; character 30, the lateral expansion of
the posterolateral portion of the quadrate; and char-
acter 39, the lateral expansion of the anterolateral
portion of the metapterygoid). In sum, these result in
a mouth form unique to S. goeldii and S. oxyrhynchus
within Sternarchorhynchus. Presumably, these modi-
fications correlate with different diets or modes of
prey capture in these species versus their congeners.
Unfortunately, the limited detailed available informa-
tion on feeding habits in, and prey items of, the
species of Sternarchorhynchus precludes a test of this
hypothesis at this time.
Clade 5, the sister lineage to clade 4, includes all
species of Sternarchorhynchus with the exception of
S. goeldii and S. oxyrhynchus. Clade 5 is character-
ized by fewer unique features that clearly involve
the feeding system and the elongate snout than is
clade 4 (character 7, the position of the posterior
limit of the dentary; character 59, the anterior
extension from the main body of the second hypo-
branchial; character 66, the presence of a scythe-
shaped process on the lateral margin of the ventral
ethmoid). Clade 7, in turn, has two unique synapo-
morphies associated with the jaws and suspenso-
rium (character 3, the compact form of the
premaxilla; character 29, the concave dorsal margin
of the quadrate). The remaining clades (8?24) either
lack or have only homoplastically distributed syna-
pomorphies associated with the food acquisition and
initial processing systems and the associated elon-
gate preorbit. The lack of further substantive modi-
fications of the jaws, suspensorium, and anterior
portion of the neurocranium at, or within, clade 8 is
likely to reflect functional constraints of those por-
tions of the head by the key innovations present at
the levels of the more inclusive clades (3, 5, 7).
As would be expected, the Bremer support values
[Treerot V.2C (Sorenson, 1999); 20 replicates and
10 000 trees] parallel the same pattern of asymmetry
in the distribution of nonhomoplastic synapomorphies
discussed above. Clade 1 (Platyurosternarchus plus
Sternarchorhynchus) has a Bremer value of 4. Within
that clade, Platyurosternarchus (clade 2) has a value
of 2, whereas Sternarchorhynchus (clade 3) with
many more synapomorphies has a value of 20. Less
inclusive basal clades and their values are: clade 4,
Bremer support 8; clade 5, Bremer support 4; clade 6,
Bremer support 5; and clade 7, Bremer support 5. The
remaining clades in the phylogeny (8?24) all have low
support values of 1 other than for clade 20, which has
a value of 2.
The overall pinnate form of the phylogeny at the
level of Platyurosternarchus and Sternarchorhynchus
and the asymmetrical distribution of the number of
species across the phylogeny (Fig. 23) evokes the phe-
nomenon discussed by Stiassny & de Pinna (1994),
who documented instances in which basal taxa within
lineages are proportionally depauperate in numbers
of species relative to their sister groups. As discussed
previously, key innovations are a potential basis for
the species richness within Sternarchorhynchus. The
underlying cause for the relatively depauperate situ-
ation in Platyurosternarchus is unknown, but some
authors (Brooks and McLennan, 1991; Hodges, 1997)
have proposed that such clades may possess
attributes that constrain diversification. Stiassny &
de Pinna (1994) also commented that basal taxa in
pinnate phylogenetic schemes often have geographi-
cally extremely constricted distributions. The broad
distribution of P. macrostoma in the immediate out-
group along with the extensive ranges of S. goeldii in
the Amazon basin and of S. oxyrhynchus of the R?o
Orinoco system of the basal clade within Sternarcho-
rhynchus run counter to the pattern highlighted by
those authors. Although the distribution of S. goeldii
and S. oxyrhynchus (Figs 42, 63) is more restrictive
than the broader Amazon basin, the river systems of
the Guyanas, and the upper Rio Paran? inhabited by
their congeners, the distributional ranges of these two
species that constitute the sister clade to all other
species of Sternarchorhynchus, nonetheless, cover sig-
nificant portions of the overall distribution of the
genus.
ADAPTIVE RADIATION
The various forms of the snout and jaws in diverse
groups of gymnotiforms are associated with differ-
ences in the diet and accessibility of certain food
items. Restructurings of the bones, musculature, and
other soft tissues of the anterior portions of the neu-
rocranium and jaws (Aguilera, 1986) in Sternarcho-
rhynchus permit the extraction of prey items from
constricted refuges in compacted clay masses, decay-
ing wood, debris, and mud on river bottoms. These
dramatic restructurings are proposed above as poten-
tial key innovations that facilitate ?grasp-suction? or
?suction assisted by mechanical grasping? in the
members of the genus. In that system, food items are
first mechanically removed from the constricted
refuges favoured by potential prey by pincer-like
manipulations of the small toothed jaws and then
drawn into the oral cavity via suction. Marrero &
Winemiller (1993) and Winemiller & Adite (1997)
266 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
pointed out that this very unusual, highly specialized
feeding mode is unique to Sternarchorhynchus and
the African mormyriform genus Campylomormyrus
amongst those orders of fishes entirely restricted to
freshwaters. Paralleling this functional similarly is
the fact that Campylomormyrus is a strikingly speci-
ose member of the Mormyridae (Feulner et al., 2007);
a situation comparable to that of Sternarchorhynchus
within the Apteronotidae. Feulner et al. (2007) pro-
posed that the phenomenon of high numbers of
species represents an adaptive radiation within
Campylomormyrus. Does that phenomenon also apply
to Sternarchorhynchus?
In his discussion on key innovations in cichlids,
Liem (1973) noted that Mayr (1960) and Bock (1965)
suggested that adaptive radiations of organisms
would not occur until the evolutionary novelty
reached a certain degree of stability or development.
The features recognized as key innovations of Ster-
narchorhynchus were primarily acquired at the level
of clade 3 and achieved a degree of stability at clade
8. More recently, Schluter (2000) defined adaptive
radiation as the evolution of ecological and phenotypic
diversity within a rapidly multiplying lineage.
Schluter proposed four criteria that characterized
that phenomenon: origin from a common ancestor,
rapid speciation, a correlation between environment
and phenotype, and trait utility.
Common ancestry
The hypothesis of the monophyly of Sternarchorhyn-
chus is supported by a series of synapomorphies
thereby filling the first of the criteria proposed by
Schluter (2000).
Rapid speciation
Rates of speciation are difficult to determine in the
absence of any evidence (i.e. detailed fossil record or
appropriate molecular data) that permits calibration
of the age of the different lineages; however, the
pronounced disparity between the two species within
Platyurosternarchus (de Santana & Vari, 2009) and
the minimum of 32 species within Sternarchorhyn-
chus (see also comments under Possible additional
undescribed species) confirm significantly different
rates of speciation and/or extinction between these
genera. No evidence of extinction exists for Platyuro-
sternarchus, the two members of which are morpho-
logically quite similar. That fact plus the broad range
of P. macrostoma across the Amazon, Orinoco, and
Essequibo river basins is congruent with the hypoth-
esis of a minimal degree of speciation within
Platyurosternarchus. Regardless of this issue, Sterna-
rchorhynchus demonstrates a significantly acceler-
ated rate of speciation over its sister clade as
evidenced by the disparity in the number of species in
each genus [two species of Platyurosternarchus (de
Santana & Vari, 2009) versus 32-plus species of Ster-
narchorhynchus (results herein); also comments in
Stiassny & Jensen (1987) concerning the need to
evaluate concepts such as species richness in a phy-
logenetic context]. At least some of the studies focused
on patterns of morphological divergence within clades
in the fossil record have demonstrated that morpho-
logical disparity typically is maximized towards the
base of the clade with that phenomenon followed by
an increase in the diversity of species (Foote, 1997).
The pattern highlighted by Foote (1997) is well
manifested in the Platyurosternarchus?Sternar-
chorhynchus lineage, wherein the basal lineages are
characterized by the possession of a disproportionate
percentage of the derived morphological modifications
known across that lineage. Within Sternarchorhyn-
chus this is followed by a dramatic increase in species
richness in clades that demonstrate relatively little
pronounced morphological restructurings in the
examined body systems.
Phenotype?environment correlation and trait utility
A correlation between environment and phenotype
as typified by phylogeny is clear in some of the
basal clades within the genus (comments at begin-
ning of Discussion above). Different forms of the
mouth in Platyurosternarchus versus Sternarcho-
rhynchus and within basal lineages of the latter
genus can be assumed to reflect different feeding
regimes permitting exploitation of specific food
resources; a difference fitting the criterion of trait
utility. The most conspicuous phenotypic differences
amongst species of Sternarchorhynchus involve
snout size and shape; more specifically differences in
the proportional length, vertical height, transverse
width and degree of central curvature of the snout.
To date we lack the necessary information on
feeding behaviours and dietary preferences to
engage in a rigorous test of the hypothesis of
phenotype?environment correlation and trait utility.
Nonetheless, the overall evidence indicates that
adaptive radiation is a driving mechanism that
accounts to some unspecified degree for the speciose
nature of Sternarchorhynchus relative to other
genera of the Apteronotidae. Further analysis incor-
porating data from life history studies of all species
in Sternarchorhynchus evaluated within a phyloge-
netic analysis is necessary to test this hypothesis.
CONVERGENCE IN ELONGATION OF SNOUT
Elongate preorbital regions of the head (= snout) are
manifested in two units of the Gymnotiformes;
the Apteronotidae (Compsaraia, Orthosternarchus,
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 267
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Platyurosternarchus, Sternarchorhamphus, Sternar-
chorhynchus, and some species of Apteronotus) and
the Rhamphichthyidae (Gymnorhamphichthys and
Rhamphichthys). In addition, both the Apteronotidae
and Rhamphichthyidae include numerous species
lacking comparable elongations of the preorbital
portion of the head. The extension of the snout in
subunits of the two families is clearly convergent
under present concepts of phylogenetic relationships
within the Gymnotiformes (Albert & Campos-da-Paz,
1998; Albert, 2001).
Focusing on the Apteronotidae, the very different
forms of the elongation of the anterior region of the
head in Compsaraia and Apteronotus relative to the
snout morphology in Sternarchorhynchus brings to
the fore questions as to the equivalence of the preor-
bital expansion in these taxa (Cox-Fernandes et al.,
2002: fig. 1; and Hilton & Cox Fernandes, 2006: fig. 1,
relative to the species of Apteronotus; and
Mago-Leccia, 1994: fig. 90, for Compsaraia compsus
identified as Porotergus compsus therein). More sig-
nificantly, neither Compsaraia nor the species of
Apteronotus with elongate preorbital regions are
closely related to Sternarchorhynchus (Albert, 2001;
Crampton & Albert, 2006; results of this study). Thus,
the elongate snouts in these other apteronotid taxa
are convergent with the lengthened preorbital portion
of the head characteristic of Sternarchorhynchus.
Elongation of the preorbital region was proposed by
Albert & Campos-da-Paz (1998) and Albert (2001) as
a feature supporting a clade within the Apteronotidae
consisting of Orthosternarchus, Platyurosternarchus,
Sternarchorhamphus, and Sternarchorhynchus. More
recently, Hilton et al. (2007) revisited this issue and
highlighted the fact that although these four genera
share an elongate preorbital region, the mode
of lengthening derives from different underlying
morphological modifications in Orthosternarchus
and Sternarchorhamphus on the one hand versus
Platyurosternarchus and Sternarchorhynchus on the
other. These differences manifest themselves most
clearly in the degree of proportional development
of the jaws that is best reflected in the relative
position of the articulation of the lower jaw with the
suspensorium.
Hilton et al. (2007) noted that the joint of the lower
jaw with the articular condyle of the quadrate
is positioned distinctly further posteriorly in
both Platyurosternarchus and Sternarchorhynchus
(Fig. 25B for position of joint in latter genus) than is
the case in Orthosternarchus tamandua and Sterna-
rchorhamphus muelleri. The combination of a poste-
rior position of the joint and an elongate snout is
achieved by pronounced proportional longitudinal
elongation of various elements of the lower jaw
(dentary, anguloarticular, Meckel?s cartilage at least
in juveniles) in Platyurosternarchus (Fig. 5) and Ster-
narchorhynchus (Figs 6, 7) relative to corresponding
elements in Orthosternarchus tamandua (Hilton
et al., 2007: fig. 12) and Sternarchorhamphus muelleri
(Campos-da-Paz, 1995: fig. 5). Snout elongation in
Orthosternarchus tamandua (Hilton et al., 2007:
fig. 11) and Sternarchorhamphus muelleri in which
the lower jaw?quadrate joint is anteriorly positioned
is in large part a function of anteroposterior elonga-
tion of elements posterior of the lower jaw?quadrate
joint; most notably the preopercle, interopercle, and
subopercle. Expansions of these ossifications in
Orthosternarchus and Sternarchorhamphus contrasts
with the more typical apteronotid morphology
of these bones in Platyurosternarchus and
Sternarchorhynchus.
Figure 25. Radiograph of head and snout of Sternarcho-
rhynchus yepezi, holotype, MCNG 44286; showing A,
expanded portion of dentary and elaboration of associated
dentition in sexually dimorphic males; B, point of articu-
lation between quadrate and lower jaw; and C, elongate
mesethmoid.
268 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Preorbital elongation results from restructuring of
two different systems in the species of Platyuroster-
narchus and Sternarchorhynchus (the anteroposterior
elongation of the components of the lower jaw and
anterior portions of the suspensorium) versus
Orthosternarchus tamandua and Sternarchorham-
phus muelleri (the anteroposterior elongation of the
posterior portion of the suspensorium and some ele-
ments of the opercular series). The lengthening of the
snout in these two lineages is thus patently nonho-
mologous, notwithstanding the external similarities
in that region in the head.
Differences also occur in the mode of preorbital
elongation and in particular in the morphology of the
jaws in Sternarchorhynchus versus its sister group,
Platyurosternarchus. Although members of each
genus have what could be considered to be elongate
preorbital regions, the mouth in Platyurosternarchus
is relatively elongate, forming 30.0?37.9% of the HL
(de Santana & Vari, 2009), whereas it is reduced in
the species of Sternarchorhynchus to a small opening
achieving a maximum of 12.4% of the HL in those
species with longer mouths.
Looking at the underlying bones, we find that the
modifications associated with the elongation of the
snout in Sternarchorhynchus are unique to that
genus, not being approximated in Platyurosternar-
chus let alone other examined apteronotids. Of par-
ticular note is the pronounced elongation of the
mesethmoid in Sternarchorhynchus (Fig. 25C), which
is a major factor in the lengthened preorbit, whereas
the frontal is only moderately extended in this genus.
In contrast, the mesethmoids in Orthosternarchus
tamandua, P. crypticus, P. macrostoma, and Sternar-
chorhamphus muelleri are of proportional lengths
comparable to those in outgroup apteronotids,
whereas these species demonstrate a pronounced
elongation of the frontals. Orthosternarchus,
Platyurosternarchus, and Sternarchorhamphus
have anteroposteriorly lengthened orbitosphenoids,
whereas Sternarchorhynchus has a form of this bone
proportionally comparable to the smaller ossification
present in apteronotid taxa with shorter snouts.
A ventral curvature of the snout that terminates
below the horizontal to opercular region was proposed
as a synapomorphy for a clade formed by Platyuro-
sternarchus, Sternarchorhynchus, and Ubidia in an
analysis by Triques (2005). Elongation of the snout
that is prerequisite for the extension of the snout to
ventral of the horizontal to opercular region was
achieved via different modifications in these genera
and as such the curvature is not homologous across
these genera.
As discussed above, grasp-suction or suction
assisted by mechanical grasping is unique to two
genera amongst freshwater fishes; Sternarchorhyn-
chus in the Neotropics and Campylomormyrus, a
member of the order Mormyriformes that inhabits
rivers in the western and central portions of sub-
Saharan Africa (Feulner et al., 2007: fig. 1). Notwith-
standing the striking convergence between these two
genera in their feeding systems, numerous differences
occur in the underlying osteological systems in Ster-
narchorhynchus versus Campylomormyrus. Given the
pronounced phylogenetic distance between these
genera, this result is expected and in the interests of
efficiency, we discuss only a few of the larger scale
differences.
The mesethmoid of Sternarchorhynchus is dis-
tinctly elongate anteroposteriorly (character 67), and
the primary contributor amongst the bones of the
dorsal portion of the neurocranium to the elongation
of the snout. In Campylomormyrus the elongation of
the preorbital region of the head is, in contrast,
largely a function of the proportional lengthening of
the frontal, with the mesethmoid being relatively
short along its anteroposterior axis (Taverne, 1968:
figs 2, 3, 6). Campylomormyrus has a distinctly
anteroposteriorly lengthened orbitosphenoid with
that elongation being one of the distinguishing
characteristics of the genus (Taverne, 1968: fig. 9).
Sternarchorhynchus, by contrast, has a relatively
anteroposteriorly compact orbitosphenoid. Finally, the
coronomeckelian ossification is lost ontogenetically in
Sternarchorhynchus (character 9), but this bone is
distinctly lengthened along the anteroposterior axis
in Campylomormyrus.
These and correlated differences in other elements
of the preorbital region in Sternarchorhynchus versus
Campylomormyrus amply demonstrate that the two
genera arrived at functionally convergent forms of
jaws and associated systems for prey capture and
ingestion via different evolutionary paths in South
America versus sub-Saharan Africa. Interesting, the
convergences in the overall external form of the pre-
orbital region of the head in Campylomormyrus and
Sternarchorhynchus correlate with the independent
acquisition in these two genera of two other features;
body elongation of varying degrees and electrogenic
abilities. A correlation between body elongation and
grasp-suction feeding may not derive directly from
this feeding mode, but rather may be functionally
associated with the requirements of the generative
and receptive systems associated with electrolocation
and electrocommunication. Both electrolocation and
electrocommunication, however, provide distinct
advantages in the habitats occupied by Campylo-
mormyrus and Sternarchorhynchus. Electrolocation
facilitates the targeting of potential prey items in the
mud, leaf litter, and interstices of clay nodules under
the limited light conditions characteristic of most
tropical rivers inhabited by Campylomormyrus and
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 269
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Sternarchorhynchus. Detection and fine-scale location
of prey is a prerequisite so that the species of these
genera can then bring into action their unique ?grasp-
suction? feeding system. Electrocommunication is also
undoubtedly critical in such habitats ?for signaling of
identity or behavior states and intentions? (Crampton
& Albert, 2006: 649) to at least congeners. As is the
case with electrolocation, this ability provides a major
advantage in the dark waters inhabited by Campylo-
mormyrus and Sternarchorhynchus on the two
continents.
SEXUAL DIMORPHISM
The comments in the introduction summarized the
several types of sexual dimorphism that occur in the
Apteronotidae. Sexual dimorphism of diverse forms,
including snout form and modifications of the lower
jaw and dentary teeth, arose several times in the
family under present hypotheses of relationships
(Rapp Py-Daniel & Cox-Fernandes, 2005). Rapp
Py-Daniel & Cox-Fernandes (2005) proposed that the
sexual dimorphism in some Sternarchorhynchus
species is most parsimoniously interpreted as having
arisen independently relative to other instances of
that phenomenon in the Apteronotidae. Our conclu-
sions, in particular the evidence supporting the
hypothesis of a sister-group relationship of Sternar-
chorhynchus with Platyurosternarchus, a genus in
which sexual dimorphism is unknown (de Santana &
Vari, 2009), are consistent with this hypothesis. The
distribution of sexual dimorphism within Sternarcho-
rhynchus reveals interesting intrageneric patterns.
The following comments should be considered with
the caveat that various species of Sternarchorhynchus
are known from limited samples, in some instances
consisting solely of probable juveniles. It is
probable that the totality of sexual dimorphism
across the genus is more extensive than presently
documented.
Survey of extensive samples of Platyurosternar-
chus, the sister group to Sternarchorhynchus, failed
to reveal sexually dimorphic features in that genus
(de Santana & Vari, 2009). A lack of such modifica-
tions similarly characterized the species of the basal
clade 4 (S. goeldii and S. oxyrhynchus) within Ster-
narchorhynchus. Lack of sexual dimorphism in the
species of clade 4 is noteworthy in that we examined
large series of specimens of all sizes of those two
species and the absence of the trait is unlikely to be
an artefact of limited samples. Evidence as to the
presence versus absence of sexual dimorphism is
unavailable for some species in clade 5 (all species of
Sternarchorhynchus with the exception of S. goeldii
and S. oxyrhynchus), but notwithstanding that limi-
tation, the phenomena manifests itself in 12 of the 22
species in clade 5 (S. axelrodi, S. caboclo, S. cramp-
toni, S. curumim, S. gnomus, S. hagedornae, S.
higuchii, S. inpai, S. mareikeae, S. mormyris, S.
retzeri, S. roseni) with those species distributed across
the clade. Sexual dimorphism within this lineage
typically involves the positions of the anus and uro-
genital papillae, with the variation in these features
sometimes correlated with sexually dimorphic colora-
tion differences.
One particularly striking form of sexual dimor-
phism is unique amongst gymnotiforms to some
members of clade 17. Some mature males in five of
the ten species in clade 17 (S. cramptoni, S. hagedor-
nae, S. higuchii, S. retzeri, S. roseni) have the ante-
rior portion of the dentary expanded both laterally
and dorsally. The resultant dorsally bulbous structure
is transversely rounded along the longitudinal axis of
the snout and surmounted by a series of enlarged
dentary teeth (Fig. 25A; also Rapp Py-Daniel &
Cox-Fernandes, 2005: fig. 5b). Males of these species
possibly use this modified lower jaw during antago-
nistic encounters (Marrero & Taphorn, 1991; Kirsch-
baum, 1995; Cox-Fernandes et al., 2002). Several of
the species within clade 17 not known to demonstrate
sexual dimorphism in the form of the lower jaw and
dentary dentition are represented by limited samples
in this study. An examination of larger samples of
those forms would be likely to reveal the presence of
these derived modifications in other species in this
lineage. These elaborations of the dentary and
dentary dentition potentially represent a complex of
synapomorphies for the species of clade 17. In the
absence of definitive information on the presence or
absence of these sexually dimorphic elaborations in
all species of clade 17, we deferred from incorporating
those features into the phylogenetic analysis. Two
other species of Sternarchorhynchus not incorporated
into the phylogenetic analysis because of limited
samples (S. taphorni, S. yepezi) also demonstrate
these pronounced elaborations of the lower jaw and
associated dentition in some mature males. Thus,
they are likely to be components of clade 17 or a
slightly more inclusive lineage.
BODY SIZE AND HABITAT
The innovations described previously potentially pro-
vided a competitive advantage to Sternarchorhynchus
relative to other clades of Apteronotidae during the
colonization of Neotropical rivers and may account for
the speciose nature of this genus within the context of
the Apteronotidae. Two other aspects of morphology
and behaviour may have contributed to the success of
the genus. Examination of body size within the
context of the arrived-at phylogeny reveals repetitive
shifts in maximum body sizes within Sternarchorhyn-
270 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
chus that probably permit the exploitation of a more
diverse suite of resources. Similarly, preferred habi-
tats for the species of the genus demonstrate definite
patterns when evaluated within the context of phy-
logeny, with such shifts further expanding the habi-
tats available to members of Sternarchorhynchus.
Platyurosternarchus, the sister group to Sternar-
chorhynchus, grows to a relatively large body size
(415 mm TL; de Santana & Vari, 2009). Basal clades
within Sternarchorhynchus (clades 4, 6) include the
largest species in the family, with examined speci-
mens of clade 4 exceeding 460 mm TL and those of
clade 6 reaching approximately 550 mm TL. Species
of clade 7 are with few exceptions of shorter to dis-
tinctly shorter maximum known body sizes, with 16
of the 20 species in that clade (S. britskii, S. caboclo,
S. chaoi, S. curumim, S. curvirostris, S. gnomus,
S. hagedornae, S. higuchii, S. inpai, S. jaimei, S.
mareikeae, S. mendesi, S. mesensis, S. montanus, S.
severii, S. stewarti) not known to achieve TLs greater
than 275 mm with some of these species sexually
mature by 150 mm TL. Body sizes of those standard
lengths apparently represent the primitive condition
for the species of clade 7. Reversals to distinctly
larger body sizes occur three times within the clade,
with all of the involved species achieving TLs of at
least 375 mm. These are S. starksi (clade 16), S.
cramptoni and S. retzeri that jointly form clade 30,
and S. roseni (clade 24).
The second transition of note within the phy-
logenetic scheme for Sternarchorhynchus involves
habitat preferences. In the discussion, we follow the
definitions used by Crampton & Albert (2006: 659)
for streams (terra firme streams and small rivers
not exposed to seasonal floodplain flooding) and
rivers (deep, swiftly flowing channels). Platyuroster-
narchus species are somewhat generalists in terms
of habitat, being collected both in streams and along
the margins of larger rivers (de Santana & Vari,
2009). The large body size Sternarchorhynchus
species of basal clades 4 and 6 (S. axelrodi, S.
goeldii, S. mormyrus, S. oxyrhynchus) are inhabit-
ants of large rivers. This is also the case for the
large body-sized S. roseni of clade 24. Such a cor-
relation between large body sizes and larger water
bodies would seem logical given the reported dietary
preferences for deep-water invertebrates that char-
acterize these species. Alternative preferences for
rapid water conditions were documented for an uni-
dentified Sternarchorhynchus species by Schwass-
mann & Carvalho (1985: 237) and this attribute has
been found to be broadly distributed across the
genus. Twelve of the 19 intermediate-sized species of
clade 7 have an overall preference for fluviatile
habitats, with the other seven species in that
lineage showing repeated independent transitions to
life in rapids. Rheophilic habits characterize S.
caboclo (clade 8), S. severii (clade 9), S. inpai (clade
11), S. mareikeae (clade 13), S. jaimei (clade 22),
and S. higuchii (clade 24). Sternarchorhynchus
hagedornae (clade 17) also lives in high-energy
stream settings albeit without evidence that it
occurs in rapids. Transitions from the ancestral riv-
erine habitat preferences thus appear to have
occurred multiple times independently within Ster-
narchorhynchus. Furthermore, S. jaimei and S.
kokraimoro, species not included in the phylogeny
because of limited samples, also were captured in
the high energy habitat of the rapids of the lower
Rio Xingu. An absence of information as to the phy-
logenetic position of these two species renders it
impossible to determine whether these represent
one or more additional independent transitions to
rheophilic conditions. Nonetheless, the evidence
indicates that rheophilic stenotopy with rapids and
other high-energy situations were acquired indepen-
dently on multiple occasions within Sternarchorhyn-
chus as was the case with at least some groups of
Neotropical cichlids (comments in Kullander & Fer-
reira, 2005). More extensive collecting efforts in
diverse habitats throughout the river systems
inhabited by the apparently rheophilic species of
Sternarchorhynchus are prerequisite for an evalua-
tion of the degree to which these species are actu-
ally exclusively stenotopic for rapids and other areas
of very rapid water flow.
Rheophily, the tendency to thrive in or have a
preference for running water, occurs in numerous
groups of South American fishes [summary in Lima
& Zuanon (2004: 120)] including other apteronotids
[e.g. Megadontognathus (Campos-da-Paz, 1999);
some species of Sternarchogiton]. Preference for
rapidly flowing water and rapids is correlated with
diverse morphological modifications in some groups
of fish, whereas in other taxa the adaptations to
high energy habitats are behavioural. We were
unable to identify morphological modifications
unique to all of the rheophilic species of Sternar-
chorhynchus to the exclusion of their congeners.
Although a long tail such as is present in some
species of the genus living in rapidly flowing waters
might on first consideration be thought to correlate
with rheophily, comparable elongations of the tail
occur amongst congeners inhabiting lentic water
bodies and slower flowing streams and rivers.
Behavioural observations of the rheophilic species of
Sternarchorhynchus in nature are lacking to date.
Nonetheless, in the absence of any manifest exter-
nal morphological shifts, it appears that the rheo-
phily typical of some species of Sternarchorhynchus
is likely to be a consequence of as-of-yet undeter-
mined behavioural adaptations.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 271
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TAXONOMIC ACCOUNTS
The dramatic increase in the number of species of
Sternarchorhynchus makes it impossible to associate
confidently many of the literature records for the
long-described species S. curvirostris, S. mormyrus,
and S. oxyrhynchus with one of the species recognized
in this revision. Particularly problematic in this
respect are citations of one or more of these species of
Sternarchorhynchus within compendia of species pur-
portedly inhabiting various rivers, regions, or coun-
tries. Myriad drainage basins and regions originally
cited as inhabited by a single species of Sternarcho-
rhynchus rather include two or more often more
members of the genus in their ichthyofaunas. We thus
restrict the synonymies for S. curvirostris, S. oxyrhyn-
chus, and S. mormyrus to the original descriptions of
the species and major subsequent publications (e.g.
Ellis, 1913; Mago-Leccia, 1994). Exceptions involve
instances where evidence in a publication or the
examination of samples that served as the basis for
the record in question allowed us to associate
unequivocally a published citation with a particular
species.
STERNARCHORHYNCHUS CASTELNAU, 1855
Sternarchorhynchus Castelnau, 1855: 91 [Campos-da-
Paz, 2000: 525, concerning page numbering; type
species: Sternarchorhynchus mulleri, Castelnau, 1855
(= Sternarchus oxyrhynchus, M?ller & Troschel,
1848); type by monotypy; masculine].
Rhamphosternarchus G?nther, 1870: 4 (type
species Sternarchus oxyrhynchus, M?ller & Troschel,
1848; type by subsequent designation of Jordan, 1919;
proposed as subgenus of Sternarchus, Bloch &
Schneider, 1801; masculine).
Sternarchorchynchus Mago-Leccia, 1978: 14
(misspelling).
Diagnosis: Synapomorphies for Sternarchorhynchus
were discussed under the preceding phylogenetic
reconstruction and are summarized in the synapo-
morphy list for the genus in Appendix 2 (clade 3).
Although these characters delimit the genus as mono-
phyletic, they overwhelmingly involve internal char-
acters and are therefore inappropriate to determine
whether whole specimens at hand are members of
Sternarchorhynchus. The following combination of
derived and plesiomorphic characters serve to delimit
members of the genus.
Sternarchorhynchus shares with other species of
the Apteronotidae the presence of a caudal fin and a
fleshy dorsal electroreceptive filament, features that
readily distinguish the family from other groups in
the Gymnotiformes. Species of Sternarchorhynchus
differ from other genera in the Apteronotidae by the
combination of the possession of an elongate, tubular
snout that is compressed laterally and slightly to
strongly curved ventrally anteriorly; the length of the
snout (usually more than 50% of HL), the small
mouth (usually less than 12% of HL), the pronounced
distance from the posterior naris to the eye
(usually more than 37% of HL), and the posterior
position of the origin of the midsaggital electrorecep-
tive filament (approximately at, or posterior to, the
middle of TL and situated approximately at 55 to 70%
of TL).
Remarks: Campos-da-Paz (2000: 527) detailed the
history of the recognition, or lack thereof, of Sternar-
chorhynchus by authors following Castlenau?s (1855)
proposal of the genus. As discussed by Campos-da-
Paz, various authors failed to recognize Sternarcho-
rhynchus for nonspecified reasons, perhaps because
they were not aware of Castlenau?s description of the
genus. G?nther (1870: 4), for example, was appar-
ently unaware of Sternarchorhynchus because he
proposed Rhamphosternarchus as a subgenus of Ster-
narchus, with that genus including three species
amongst which was S. oxyrhynchus, the type species
of Sternarchorhynchus. The Rhamphosternarchus of
G?nther was based on the presence in member
species of a ?snout produced into a long tube?, one of
the distinguishing attributes for Sternarchorhynchus.
Eigenmann & Ward (1905: 166) rectified the problem
by explicitly noting that Rhamphosternarchus was a
synonym of Sternarchorhynchus.
Common features of species of Sternarchorhynchus:
The species of Sternarchorhynchus share a distinc-
tive bauplan with many of the features delimiting
species involving meristics and specific morphomet-
ric features and/or coloration rather than significant
changes in overall external head and/or body mor-
phology. In the interest of space efficiency, we
describe external features common to all species of
Sternarchorhynchus in this section rather than reit-
erating them in each species description. Conditions
of the intragenerically variable external features for
each species are detailed in each species account.
Body elongate and distinctly laterally compressed
(cultiform), more so in region posterior to abdominal
region. Greatest body depth located in area of abdomi-
nal cavity or slightly posterior to that region. Dorsal
profile of body ranges between straight to very
slightly convex. Anteriormost perforated lateral line
scale located along vertical through pectoral-fin
origin.
Head laterally compressed, widest in opercular
region and deepest at nape. Eye very small, laterally
positioned on dorsal half of head, and completely
272 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
covered by thin membrane. Cephalic pores small.
Snout distinctly elongate, overall tubular but some-
what compressed laterally. Premaxilla of small size.
Anterior naris located at end of small tube and proxi-
mate to tip of snout. Posterior naris ellipsoid, without
tubular extension. Posterior naris located distinctly
closer to tip of snout than to anterior margin of eye.
Branchial opening constricted to short vertical aper-
ture situated along posterior margin of opercle and
slightly anterior to vertical through pectoral-fin
origin. Branchial membranes joined at isthmus. Anus
and urogenital papilla adjacent and ventrally posi-
tioned. Location of both structures intragenerically
and ontogenetically variable in many species and
sexually dimorphic in some species.
Scales cycloid, small and present over all, or nearly
all, of body from rear of head to anterior portion of
base of caudal fin. Scales absent or sparse in some
species along mid-dorsal line of body anterior to
origin of electroreceptive filament. Lateral line scales
often larger than those of scale rows immediately
dorsal and ventral of lateral line series.
Pectoral fin long, broad, and distally pointed. Anal
fin elongate and extending from under head posteri-
orly for most of length of body. Dorsal electroreceptive
filament arising on posterior portion of body and
progressively narrowing posteriorly and inserting into
and attached to narrow mid-dorsal grove. Caudal and
pectoral fins present, but dorsal and pelvic fins absent
as in all gymnotiforms.
Distribution: A distinct majority of the species of
Sternarchorhynchus inhabit portions of the Amazon
basin (22 of 32 species, Table 1), with the genus
occurring across major portions of that drainage
system. Many of the apparent major gaps in the
distribution of the genus across the Amazon basin
are most likely to be a function of the lack of col-
lecting in habitats appropriate for the members of
the genus. This issue is general for the Neotropical
freshwater fish fauna (Vari & Malabarba, 1998).
Seven species of Sternarchorhynchus occur in the
R?o Orinoco system and the independent river
systems of north-eastern Venezuela that drain into
the Golfo de Paria (Table 1). One of these species, S.
mormyrus, is the only member of the genus shared
with the Amazon basin (comments under that
species description).
The sparse records of Sternarchorhynchus in the
rivers of the Guianas (two species) may be in part a
function of the limited collecting efforts in appropriate
habitats, but the genus is unknown even in some
relatively well sampled basins in this region (Mol
et al., 2007). Similar gaps in distributions at the
generic level occur in other components of the ich-
thyofauana in the Guianas. A single species of Ster-
narchorhynchus occurs in the Essequibo River system
of Guyana, one species in the Lawa River of the
Marowijne River (= Fleuve Maroni) system along the
border between Suriname and French Guiana. Ster-
narchorhynchus has also been reported from the
Fleuve Oyapock (= Rio Oiapoque) along the boundary
between French Guiana and Brazil (Planquette,
Keith & Le Bail, 1996: 406). We were unable to
examine the specimens that served as the basis for
that report. A single species of Sternarchorhynchus, S.
britskii, is known from the upper portions of the Rio
Paran? basin in Brazil; that being the only member of
the genus occurring in a drainage system south of the
Amazon basin.
Diversity: The 32 recognized species of Sternarcho-
rhynchus represent approximately 40% of the present
known diversity at the species level within the Apter-
onotidae, making it by far the most speciose genus in
the family, with the approximately 15 recognized
species of Apteronotus (sensu stricto; Albert & Cramp-
ton, 2005: 363) making it the next most diverse genus
in the family. As we note under the Possible addi-
tional undescribed species section, the 32 recognized
species of Sternarchorhynchus undoubtedly represent
an underestimate of the actual diversity in the genus.
Under present concepts of generic limits and species
richness, Sternarchorhynchus is one of the most spe-
ciose genera within the Gymnotiformes. Only Gym-
notus in the Gymnotidae, that is estimated to
include at least 35 species (Albert & Crampton,
2005; Albert et al., 2005) is as speciose as
Sternarchorhynchus.
An evaluation of the diversity of Sternarchorhyn-
chus relative to that of Gymnotus shows some notable
differences in the proportional density of species in
the two genera across their range. Most obviously,
Sternarchorhynchus is restricted to the cis-Andean
portions of South America with only one species, S.
britskii, known from a river basin south of the
Amazon, whereas Gymnotus has a massive distribu-
tion from Mexico to Argentina to both sides of the
Andean Cordilleras. Gymnotus is, furthermore, able
to tolerate a much broader range of habitats, being
able to absorb atmospheric oxygen via a portion of the
gas-bladder (Campos-da-Paz, 2003: 483); an adapta-
tion that opens up low oxygen-level backwaters and
swamps as potential habitats. Sternarchorhynchus
lacks such modifications and is apparently limited to
well-oxygenated habitats. The more restricted geo-
graphical range and habitat tolerances of the species
of Sternarchorhynchus render its speciose nature all
the more impressive in terms of proportional density
of species. In part this density is made possible by the
ability by many species of Sternarchorhynchus to
exploit deep river habitats, which contrasts with the
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 273
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
absence of all genera of the Gymnotidae from such
habitats (Crampton, 2007: 302).
Remarks on secondary sexual dimorphism: Various
species within one clade within Sternarchorhynchus
together with various other Gymnotiformes (e.g.
Sternarchogiton; de Santana & Crampton, 2007: 390:
fig. 1a; Compsaraia, Albert & Crampton, 2009: fig. 1)
demonstrate particularly striking sexual dimorphic
remodelling of the lower jaw of various forms. Some
males with well-developed testes amongst the Ster-
narchorhynchus species in clade 17 have the dentary
anteriorly lengthened and transversely expanded into
a dorsally bulbous structure that is rounded from a
dorsal view (Fig. 25A; comments on Sexual dimor-
phism under Discussion above). This enlarged portion
of the dentary bears a patch of distinctly enlarged,
typically slightly posteriorly recurved dentition. This
patch of enlarged teeth in males of this clade may be
utilized in confrontations during breeding contests
(Marrero & Taphorn, 1991: 129).
Such dramatic elaborations of the lower jaw and
dentary dentition are unknown in some species of the
clade represented by limited numbers of specimens
and larger samples are necessary to determine
whether the condition is indeed absent in these
species. We have examined conspecific males of the
species characterized by such dentary modifications
Table 1. Occurrence of the species of Sternarchorhynchus in river systems and regions of cis-Andean South America
Species
River basins and regions
A B C D E F G H I J K L
S. axelrodi x x
S. britskii x
S. caboclo x
S. chaoi x
S. cramptoni x x x
S. curumim x
S. curvirostris x
S. freemani x
S. galibi x
S. gnomus x
S. goeldii x x x x
S. hagedornae x
S. higuchii x
S. inpai x
S. jaimei x
S. kokraimoro x
S. mareikeae x
S. marreroi x
S. mendesi x
S. mesensis x
S. montanus x
S. mormyrus x x x x
S. oxyrhynchus x
S. retzeri x x x
S. roseni x
S. schwassmanni x
S. severii x
S. starksi x
S. stewarti x
S. taphorni x
S. yepezi x
S. villasboasi x
River systems and regions are as follows: A, Rio Orinoco basin; B, Guianas; C, Rio Negro; D, Rio Tocantins/Araguaia; E,
Rio Trombetas; F, mainstream Amazon below Manaus; G, mainstream Amazon above Manaus; H, Rio Madeira; I, western
Amazonian tributaries; J, upper Rio Paran?; K, Rio Xingu; L, Rio Branco.
274 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
with well-developed testes that nonetheless lack
elaborations of the lower jaw and associated denti-
tion. This is despite those individuals being of body
sizes comparable to conspecific males with those
attributes. Thus, one cannot assume that large speci-
mens of a species within clade 17 that lack an expan-
sion of the dentary and elaborations of the dentary
dentition are females. The significance of these dif-
ferences amongst conspecific males of comparable
sizes cannot be elucidated from museum specimens,
but potentially reflects social structure amongst
groups of males. Alternatively, it may be a function of
seasonality in the manifestation of this secondary
sexually dimorphic feature.
STERNARCHORHYNCHUS AXELRODI SP. NOV.
(FIGS 26?28; TABLE 4)
Sternarchorhynchus cf. mormyrus, Campos-da-Paz,
2000: 533 [Brazil, Rio Tocantins; as probable unde-
scribed species].
Sternarchorhynchus mormyrus, not of Stein-
dachner, dos Santos et al., 2004: 103, unnumbered
figure [Brazil, lower Rio Tocantins; food habits].
Diagnosis: Sternarchorhynchus axelrodi is distin-
guished from all congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical through
the anterior nares, the absence of scales along the
mid-dorsal region of the body as far posteriorly as the
origin of the electroreceptive filament, and the pos-
session of 200?217 anal-fin rays.
Description: Morphometric data for examined speci-
mens in Table 4.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
curved ventrally, and with sexual dimorphism in
overall form across examined specimens of large body
sizes. Snout more anteroventrally aligned in mature
females than in mature males of comparable sizes as
evidenced by specimens of each sex with mature
gonads. Sexual dimorphism in form of lower jaw and
associated dentition found in many congeners not
apparent in examined samples. Mouth terminal,
rictus situated anterior of vertical through anterior
naris. Anus and urogenital papilla located ventral to
head, with openings situated anterior to vertical
through anterior margin of eye (in specimens of 433?
510 mm SL). Combined opening for anus and urogeni-
tal papilla distinctly elongate longitudinally and
bordered laterally by raised fleshy ridges.
Premaxilla with six to ten teeth apparent in whole
specimens (N = 4). Dentary with one tooth row con-
sisting of nine to 15 curved conical teeth in whole
specimens (N = 4), with second row of apparent
replacement teeth located internal to functional row.
Branchiostegal rays five; with first to third rays
apparently narrow and elongate in radiographs, and
with fourth and fifth rays clearly very large and
broad. Precaudal vertebrae 18?19 (15 anterior; three
to four transitional; N = 10).
Pectoral-fin rays ii + 13?17 [ii + 16] (N = 10). Anal-
fin origin located anterior to opercle. Anterior
unbranched anal-fin rays 22?34 [33] (N = 5). Total
anal-fin rays 200?217 [205] (N = 10). Scales above
lateral line at midbody nine to 11 [11] (N = 10). Scales
absent along much of mid-dorsal line in region ante-
rior to origin of midsaggital electroreceptive filament.
Areas lacking scales sometimes separated by regions
covered by mid-dorsal scales, but with position and
extent of regions lacking scales variable across exam-
ined specimens. Origin of midsaggital electrorecep-
tive filament located approximately at 65% of TL.
KEYS TO THE SPECIES OF STERNARCHORHYNCHUS
Keys are presented for the species of Sternarchorhynchus by major drainage basins (Amazon, Orinoco, Paran?) or
region (Guianas) because each of those units have largely endemic faunas of Sternarchorhynchus species. As an aid
to the identification of species, their distributions are detailed in Table 1. The alternative of a single, all-inclusive key
for all members of the genus would be quite complex and involve working through multiple couplets in order to identify
materials of many species only one of which (S. mormyrus) occurs in more than one river basin (Amazon plus Orinoco).
Sternarchorhynchus mormyrus is included in the keys for the species in both of those basins. The diagnoses under each
species account serve to separate differentially each species from all congeners. Sternarchorhynchus mesensis
demonstrates variation in the degree to which the narrow, lightly coloured stripe on the head and body is obvious.
Some specimens of the species in isolation might be considered to lack the stripe and the species consequently appears
in two places in the key for the members of the genus in the Amazon basin.
Differences in anal-fin ray numbers, both anterior unbranched and total rays, proved to be the most informative
meristic features for distinguishing Sternarchorhynchus species. Frequency distributions of these values for the
species are provided in Tables 2 and 3 to assist readers with the identification of specimens at hand. Supplementing
the information in the keys, diagnoses, and tables are the phylogenetically informative characters discussed under
Character description and analysis. That evidence underpins our recognition of multiple species within a well-resolved
hypothesis of relationships. Autapomorphies characterizing a number of species are listed in Appendix 2.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 275
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
KEY TO THE SPECIES OF STERNARCHORHYNCHUS OCCURRING IN THE AMAZON BASIN
1. Gape of mouth aligned with main axis of snout, with gape elongate and extending posteriorly distinctly beyond
vertical through posterior naris .................................................................................S. goeldii sp. nov.
Gape short, terminates posteriorly at, or slightly anterior of, vertical through anterior naris........................2
2. Scales either lacking or sparse and covered by skin middorsally at least in part of region from rear of head to
insertion of electroreceptive filament ...................................................................................................3
Scales present and obvious along mid-dorsal region of body from rear of head to insertion of electroreceptive
filament.........................................................................................................................................9
3. Mid-dorsal scales missing along entire mid-dorsal region to insertion of electroreceptive filament ..................4
Mid-dorsal scales either sparse and covered by skin, or missing along mid-dorsal region solely from rear of head
to point approximately along vertical through rear of pectoral fin ............................................................ 5
4. Total anal-fin rays 200?217.....................................................................................S. axelrodi sp. nov.
Total anal-fin rays 222?245................................................................................................S. mormyrus
5. Dorsal portion of head and body with at most obscure mid-dorsal, lightly coloured stripe on head...................
.........................................................................................................................S. higuchii sp. nov.
Dorsal portion of head and body with distinct narrow mid-dorsal, lightly coloured stripe on head and often on
body..............................................................................................................................................6
6. Mid-dorsal scales completely absent along body approximately to vertical through rear of pectoral fin............7
Mid-dorsal region of body with scales present, but sparse and covered by skin...........................................8
7. Lateral line extending posteriorly to point three scales short of base of caudal fin; total anal-fin rays 165?178,
premaxilla with eight to 13 teeth, postocular distance 39.4?41.3% of HL ............................S. chaoi sp. nov.
Lateral line extending posteriorly to base of caudal fin; total anal-fin rays 180?195, premaxilla with four to seven
teeth, postocular distance 41.5?49.1% of HL.................................................................S. jaimei sp. nov.
8. Anterior unbranched anal-fin rays 32?35, total anal-fin rays 173?193, length of anal-fin base 86.6?89.6% of LEA,
head depth at nape 53.1?59.2% of HL.................................................................S. hagedornae sp. nov.
Anterior unbranched anal-fin rays 25?26, total anal-fin rays 164?166, length of anal-fin base 80.2?83.9% of LEA,
head depth at nape 49.5?49.6% of HL.............................................................S. schwassmanni sp. nov.
9. Mid-dorsal region of head and body without narrow, lightly coloured stripe..............................................10
Mid-dorsal region of head and body with distinct, narrow, lightly coloured stripe......................................13
10. Lateral line extending posteriorly to point three to five scales short of base of caudal fin, eight to nine series of
scales present above lateral line in mid-dorsal region of body ..................................S. kokraimoro sp. nov.
Lateral line extending posteriorly to base of caudal fin, ten to 13 series of scales present above lateral line in
mid-dorsal region of body.................................................................................................................11
11. Total anal-fin rays 153?174, branchiostegal rays four .................................................................S. caboclo
Total anal-fin rays 171?189, branchiostegal rays five............................................................................12
12. Premaxillary teeth seven to ten, teeth in outer tooth row of dentary seven to eight, prepectoral-fin distance
18.3?20.6% of LEA, internarial distance 2.4?2.8% of HL .......................................................... S. curumim
Premaxillary teeth 11?14, teeth in outer row of dentary ten to 11, prepectoral-fin distance 21.4?23.8% of LEA,
internarial distance 3.2?4.7% of HL......................................................................................S. mesensis
13. Mid-dorsal lightly coloured stripe limited to head ................................................................................ 14
Mid-dorsal lightly coloured stripe commencing on snout and extending posteriorly to insertion of electroreceptive
filament........................................................................................................................................17
14. Lateral line extending posteriorly to point four to eight scales anterior of base of caudal fin.......................15
Lateral line extending posteriorly to base of caudal fin.........................................................................16
15. Total anal-fin rays 156?167, caudal length 12.6?15.6% of LEA, postocular distance 33.1?41.1% of HL, anal fin
somewhat dusky, but not dark.....................................................................................S. inpai sp. nov.
Total anal-fin rays 186, caudal length 6.8% of LEA, postocular distance 43.5?46.4% of HL, anal fin dark.........
.........................................................................................................................S. taphorni sp. nov.
16. Premaxillary teeth 12?13, teeth in outer row of dentary 12?13, tip of electroreceptive filament located four to seven
scales posterior of vertical through termination of base of anal fin, pectoral-fin length 35.0?40.9% of HL, postocular
distance 36.0?41.3% of HL...................................................................................S. mareikeae sp. nov.
Premaxillary teeth eight to nine, teeth in outer row of dentary eight to nine, tip of electroreceptive filament located
two scales posterior of vertical through termination of base of anal fin, pectoral-fin length 43.6?47.1% of HL,
postocular distance 44.4?46.0% of HL...................................................................S. villasboasi sp. nov.
17. Distal portions of anal fin with dark band covering one-third to one-half of most of fin rays and sometimes all of
posterior rays ................................................................................................................................ 18
Distal potions of anal fin without distinct dark band............................................................................20
276 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
18. Postocular distance 31.6?34.9% of HL, caudal length 7.1?10.3% of LEA............................S. retzeri sp. nov.
Postocular distance 37.4?43.7% of HL, caudal length 5.3?8.4% of LEA....................................................19
19. Premaxillary teeth eight to 12, distance from anus to snout 8.9?12.0% of LEA, pectoral-fin length 38.0?46.5% of
HL, tail depth 23.6?29.6% of caudal length ............................................................S. cramptoni sp. nov.
Premaxillary teeth six to seven, distance from anus to snout 6.9?7.3% of LEA, pectoral-fin length 47.8?49.1% of
HL, tail depth 21.2?21.7% of caudal length.............................................................S. montanus sp. nov.
20. Anal fin distinctly dark basally...........................................................................S. curvirostris sp. nov.
Anal fin hyaline or slightly dusky, but not distinctly dark basally .......................................................... 21
21. Caudal length 6.1?7.1% of LEA ...............................................................................S. stewarti sp. nov.
Caudal length 9.0?16.5% of LEA ...................................................................................................... 22
22. Preanal distance 14.2?17.0% of LEA, head length 20.5?23.6% of LEA, pectoral-fin length 27.0?35.3% of HL.....
.......................................................................................................................................S. mesensis
Preanal distance 9.4?12.7% of LEA, head length 14.8?18.1% of LEA, pectoral-fin length 40.6?53.2% of HL ......
...........................................................................................................................S. starksi sp. nov.
KEY TO THE SPECIES OF STERNARCHORHYNCHUS OCCURRING IN THE R?O ORINOCO BASIN
1. Gape of mouth aligned with main axis of snout, with gape elongate and extending posteriorly distinctly beyond
vertical to posterior naris.................................................................................................S. oxyrhynchus
Gape short, terminates posteriorly at, or slightly anterior of, vertical through anterior naris..........................2
2. Mid-dorsal region of head and body without narrow, lightly coloured stripe or stripe obscure.............S. gnomus
Mid-dorsal region of head and body with distinct, narrow, lightly coloured stripe ......................................... 3
3. Scales along mid-dorsal region of body either lacking along at least part of region or scales sparse and covered by
scales..............................................................................................................................................4
Scales present and obvious along mid-dorsal region of body from rear of head to insertion of electroreceptive
organ...................................................................................................................S. marreroi sp. nov.
4. Total anal-fin rays 174?188.................................................................................................................5
Total anal-fin rays 193?245.................................................................................................................6
5. Total anal-fin rays 174?182; anterior unbranched anal-fin rays 29?46; postocular distance 38.8?40.8% of LEA;
caudal-fin length 18.1?33.0% of caudal length; scales above lateral line at midbody six to nine ........................
...........................................................................................................................S. mendesi sp. nov.
Total anal-fin rays 182?188; anterior unbranched anal-fin rays 23?29; postocular distance 43.8?46.2% of LEA;
caudal-fin length 38.8% of caudal length; scales above lateral line at midbody nine to 12.......S. yepezi sp. nov.
6. Total anal-fin rays 193?210; lightly coloured mid-dorsal stripe present from tip of snout to origin of electroreceptive
organ; mid-dorsal region of body scaled.......................................................................................S. roseni
Total anal-fin rays 222?245; mid-dorsal region of head and body uniformly coloured; mid-dorsal region of body
lacking scales....................................................................................................................S. mormyrus
KEY TO THE SPECIES OF STERNARCHORHYNCHUS OCCURRING IN THE COASTAL BASINS OF GUYANA
AND SURINAME
1. Caudal length 8.7?10.8% of LEA; distance from anus to anal-fin insertion 6.8?12.8% of LEA; tail depth 13.8?19.2%
of caudal length; premaxilla with six to ten teeth............................................................S. galibi sp. nov.
Caudal length 15.1?16.9% of LEA; distance from anus to anal-fin insertion 13.0?17.4% of LEA; tail depth 8.0?8.9%
of caudal length; premaxilla with four to five teeth......................................................S. freemani sp. nov.
SPECIES OF STERNARCHORHYNCHUS OCCURRING IN THE UPPER RIO PARAN? BASIN
Only a single Sternarchorhynchus species, S. britskii, is known from the upper Rio Paran? basin or indeed across the
R?o de La Plata system. Sternarchorhynchus britskii can be distinguished by all congeners by the features listed in
the Diagnosis for that species.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 277
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Filament extending posteriorly to point four scales
anterior of vertical through posterior terminus of base
of anal fin. Tail compressed and short, ending in
small, elongate, pointed caudal fin. Caudal-fin rays
16?20 [19] (N = 10).
Coloration in alcohol: Overall ground coloration
brown. Head dark overall with more concentrated
band of dark chromatophores present along dorsal
portion of snout in region from vertical through pos-
terior naris to slightly posterior of eye; dark pigmen-
tation in some individuals extending anteriorly nearly
to tip of snout. Body brown overall, with pigmentation
darker dorsally, but without any distinct pigmenta-
tion pattern other than for dark mid-dorsal coloration
in those regions that lack scales.
Pectoral fin dark, more so distally and sometimes
nearly completely very darkly pigmented. Anal fin
dark overall with distal pigmentation distinctly
darker and forming irregular band. Caudal fin largely
unpigmented, but with some individuals having vari-
able dark pigmentation approximately midway along
its length.
Distribution: Most examined specimens of S. axelrodi
originated at one location in the upper portions of the
Rio Tocantins basin; however, a single lot of the
species collected in the lower portions of that river
system at Tucuru? demonstrates that the species is
broadly distributed along the Rio Tocantins (Fig. 28).
Ecology: The type locality of S. axelrodi was reported
as a clear water system with the bottom formed by
small stones and rocks (Vari & Harold, 2001: 164). dos
Santos et al. (2004: 103; species cited therein as
S. mormyrus) report that the species grows to
600 mm TL and feeds on insects and other aquatic
invertebrates.
Secondary sexual dimorphism: Sternarchorhynchus
axelrodi demonstrates pronounced secondary sexual
dimorphism in the overall form of the snout. Large
males with mature testes have the snout slightly
curved ventrally, whereas mature females with well-
developed ovaries have a more pronounced ventral
curvature of the snout (compare Figs 26, 27). No
secondary sexual dimorphism of the dentary and
lower jaw dentition comparable to that present in
some congeners was apparent in the available
samples of the species.
SPECIES ACCOUNTS
In order to facilitate the location of individual species accounts and cross references between them, the species
descriptions are arranged alphabetically within Sternarchorhynchus rather than by region of occurrence or phyloge-
netic affinity. Species accounts are followed by a discussion (Possible Additional Undescribed Species) of population
samples that represent likely undescribed species of Sternarchorhynchus that are not formally described at this time.
Figure 26. Sternarchorhynchus axelrodi sp. nov., holotype, male, 444 mm total length, MNRJ 31279; Brazil, Goi?s,
Rio Tocantins.
Figure 27. Sternarchorhynchus axelrodi sp. nov.,
paratype, female, 493 mm total length, MNRJ 12168;
Brazil, Goi?s, Rio Tocantins; showing more pronounced
ventral curvature of snout in mature females of species.
278 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
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1
S
.
ch
ao
i
1
1
1
1
1
1
1
1
S
.
cr
am
pt
on
i
1
3
3
2
1
1
1
2
1
S
.
cu
ru
m
im
1
1
S
.
cu
rv
ir
os
tr
is
1
S
.
fr
ee
m
an
i
1
2
1
S
.
ga
li
bi
2
2
1
2
1
S
.
gn
om
u
s
2
1
1
S
.
go
el
d
ii
1
1
3
2
3
1
1
1
1
1
1
S
.
h
ag
ed
or
n
ae
1
1
1
1
1
1
S
.
h
ig
u
ch
ii
1
2
4
3
2
1
1
S
.
in
pa
i
1
1
1
S
.
ja
im
ei
1
1
1
1
S
.
ko
kr
ai
m
or
o
1
1
S
.
m
ar
ei
ke
ae
1
2
2
2
1
S
.
m
ar
re
ro
i
1
1
1
S
.
m
en
d
es
i
1
1
1
2
1
1
S
.
m
es
en
si
s
1
2
1
1
S
.
m
on
ta
n
u
s
1
1
S
.
m
or
m
yr
u
s
2
4
3
3
1
1
S
.
ox
yr
h
yn
ch
u
s
1
1
3
2
S
.
re
tz
er
i
1
2
2
3
1
1
2
S
.
ro
se
n
i
1
1
3
1
3
3
4
2
S
.
sc
h
w
as
sm
an
n
i
1
1
S
.
se
ve
ri
i
1
1
1
S
.
st
ar
ks
i
1
2
2
1
3
S
.
st
ew
ar
ti
6
4
4
3
1
2
S
.
ta
ph
or
n
i
1
S
.
ye
pe
zi
1
2
S
.
vi
ll
as
bo
as
i
1
1
1
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 279
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
T
a
b
le
3.
F
re
qu
en
cy
of
di
st
ri
bu
ti
on
of
to
ta
l
an
al
-fi
n
ra
ys
in
sp
ec
ie
s
of
S
te
rn
ar
ch
or
h
yn
ch
u
s
15
3
15
7
16
1
16
5
16
9
17
3
17
7
18
1
18
5
18
9
19
3
19
7
20
1
20
5
20
9
21
3
21
7
22
1
22
5
22
9
23
3
23
7
24
1
24
5
S
.
ax
el
ro
d
i
1
4
2
3
S
.
br
it
sk
ii
1
3
1
2
S
.
ca
bo
cl
o
1
1
3
2
3
1
S
.
ch
ao
i
3
3
3
1
S
.
cr
am
pt
on
i
1
2
1
3
8
4
4
S
.
cu
ru
m
im
1
1
S
.
cu
rv
ir
os
tr
is
2
2
1
1
S
.
fr
ee
m
an
i
2
1
1
S
.
ga
li
bi
4
3
3
S
.
gn
om
u
s
1
3
2
1
2
S
.
go
el
d
ii
2
5
7
7
1
3
1
1
S
.
h
ag
ed
or
n
ae
2
1
1
1
1
1
S
.
h
ig
u
ch
ii
2
2
7
3
1
S
.
in
pa
i
1
2
3
S
.
ja
im
ei
1
1
1
3
1
1
1
S
.
ko
kr
ai
m
or
o
1
1
S
.
m
ar
ei
ke
ae
1
5
2
1
1
S
.
m
ar
re
ro
i
1
1
S
.
m
en
d
es
i
2
2
3
S
.
m
es
en
si
s
1
3
1
1
S
.
m
on
ta
n
u
s
1
1
S
.
m
or
m
yr
u
s
2
3
2
3
5
S
.
ox
yr
h
yn
ch
u
s
3
2
6
1
S
.
re
tz
er
i
2
2
4
2
4
1
S
.
ro
se
n
i
3
4
7
5
2
S
.
sc
h
w
as
sm
an
n
i
1
1
S
.
se
ve
ri
i
2
1
4
S
.
st
ar
ks
i
2
1
3
1
3
1
S
.
st
ew
ar
ti
6
7
3
1
S
.
ta
ph
or
n
i
S
.
ye
pe
zi
1
2
S
.
vi
ll
as
bo
as
i
1
1
1
1
A
n
al
-fi
n
ra
y
co
u
n
ts
ar
ra
n
ge
d
in
gr
ou
ps
of
fo
u
r
st
ar
ti
n
g
w
it
h
li
st
ed
n
u
m
be
r.
280 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Etymology: The species name, axelrodi, is in honour of
Dr Herbert Axelrod, whose generous support of ich-
thyological research assisted with the completion of
this project.
Remarks: Sternarchorhynchus axelrodi was collected
at the same locality as the type series of S. mesensis.
The two species differ in various features including
the total number of anal-fin rays (200?217 versus
171?189, respectively), caudal-fin rays (16?20 versus
13?15, respectively), coloration of the mid-dorsal
portion of the body anterior to the origin of the
electroreceptive filament (with distinct, narrow,
lightly coloured stripe versus dark or sometimes with
indistinct lightly coloured region, respectively), the
greatest body depth (13.5?17.6 versus 10.0?12.3% of
LEA, respectively), the caudal length (4.9?6.7 versus
9.0?14.3% of LEA, respectively), and other features.
Material examined
Holotype: ? BRAZIL. Goi?s: Munic?pio de Mina?u/
Cavalcante, Rio Tocantins, at future site of Usina
Hidroel?ctrica Serra da Mesa (approximately 13?44?S,
48?08?W), collected by D. F. Moraes, C. N. Ricci,
O. Roppa, vii.1988; MNRJ 31279 (444).
Paratypes: ? BRAZIL. Goi?s: Munic?pio de Mina?u/
Cavalcante, Rio Tocantins, at future site of Usina
Hidroel?trica Serra da Mesa (approximately 13?44?S,
48?08?W), collected with holotype by D. F. Moraes,
C. N. Ricci, O. Roppa, vii.1988; MNRJ 12168,
8 (433?530), USNM 391570, 1 (475).
Nontype specimens: ? BRAZIL. Goi?s: Munic?pio de
Mina?u/Cavalcante, Rio Tocantins, at future site of
Usina Hidroel?ctrica Serra da Mesa (approximately
13?44?S, 48?08?W), collected with holotype; MNRJ
31244,1 (not measured); MNRJ 31245, 1 (not mea-
sured); MNRJ 31246, 1 (not measured). Par?: INPA
27484, 2 (300?360); Rio Tocantins, Tucuru?, Mercado
de Camet?.
STERNARCHORHYNCHUS BRITSKII CAMPOS-dA-PAZ
(FIGS 28, 29; TABLE 4)
Sternarchorhynchus sp. Britski, 1972: 91 [first cita-
tion of Sternarchorhynchus from Rio Paran? basin,
Brazil].
Sternarchorhynchus curvirostris, not of Boulenger,
Triques, 1993: 91 [details of osteology].
Figure 28. Map of central and northern South America showing geographical distribution of Sternarchorhynchus
axelrodi sp. nov. (1 = holotype locality), Sternarchorhynchus britskii, Sternarchorhynchus caboclo, Sternarchorhyn-
chus chaoi sp. nov. (2 = holotype locality), and Sternarchorhynchus cramptoni sp. nov. (3 = holotype locality) (some
symbols represent more than one locality and/or lot of specimens).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 281
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
T
a
b
le
4.
M
or
ph
om
et
ri
cs
fo
r
ex
am
in
ed
sp
ec
im
en
s
of
S
te
rn
ar
ch
or
h
yn
ch
u
s
ax
el
ro
d
i,
S
te
rn
ar
ch
or
h
yn
ch
u
s
br
it
sk
ii
,
an
d
S
te
rn
ar
ch
or
h
yn
ch
u
s
ca
bo
cl
o
(p
ar
at
yp
es
,
IN
P
A
10
59
4)
S
.
ax
el
ro
d
i
S
.
br
it
sk
ii
S
.
ca
bo
cl
o
H
P
ar
at
yp
es
M
ea
n
H
R
an
ge
M
ea
n
H
P
ar
at
yp
es
M
ea
n
To
ta
l
le
n
gt
h
(m
m
)
44
4
43
3?
53
0
(N
=
9)
?
26
1
20
9?
25
0
(N
=
14
)
?
22
5
46
.3
?2
26
(N
=
57
)
?
L
en
gt
h
to
en
d
of
an
al
fi
n
(m
m
)
42
0
41
0?
51
0
(N
=
9)
?
24
2
17
9?
23
2
(N
=
11
)
?
20
6
41
.1
?2
06
(N
=
57
)
?
H
ea
d
le
n
gt
h
(m
m
)
99
.9
93
.7
?1
15
.9
(N
=
9)
?
47
.5
33
.1
?4
6.
9
(N
=
14
)
?
39
.2
8.
7?
39
.2
(N
=
57
)
?
C
au
da
l
le
n
gt
h
(m
m
)
23
.3
24
.9
?3
0.
5
(N
=
9)
?
19
.2
12
.0
?1
92
(N
=
10
)
?
16
.8
8.
7?
21
.6
(N
=
57
)
?
P
er
ce
n
t
of
le
n
gt
h
to
en
d
of
an
al
fi
n
A
n
al
-fi
n
ba
se
83
.3
76
.9
?9
7.
1
(N
=
9)
85
.1
87
.6
86
.4
?9
3.
0
(N
=
11
)
88
.3
84
.0
79
.3
?8
6.
4
(N
=
57
)
83
.1
D
is
ta
n
ce
sn
ou
t
to
an
u
s
8.
5
4.
6?
8.
1
(N
=
9)
6.
9
?
?
?
11
.2
11
.2
?1
4.
9
(N
=
10
)
12
.9
P
re
an
al
-fi
n
di
st
an
ce
16
.5
14
.1
?1
8.
5
(N
=
9)
15
.9
13
.3
12
.5
?1
5.
8
(N
=
11
)
13
.5
16
.4
12
.1
?2
0.
0
(N
=
57
)
16
.6
P
re
pe
ct
or
al
-fi
n
di
st
an
ce
24
.3
22
.1
?2
5.
7
(N
=
9)
24
.0
20
.1
19
.4
?2
3.
6
(N
=
11
)
21
.1
21
.1
17
.4
?2
5.
1
(N
=
57
)
21
.5
G
re
at
es
t
bo
dy
de
pt
h
14
.4
13
.5
?1
7.
6
(N
=
9)
15
.1
14
.1
12
.1
?1
5.
7
(N
=
13
)
14
.3
11
.0
11
.3
?1
4.
7
(N
=
57
)
12
.7
H
ea
d
le
n
gt
h
23
.7
21
.8
?2
5.
1
(N
=
9)
23
.4
19
.6
18
.9
?2
3.
1
(N
=
14
)
20
.1
19
.0
15
.6
?2
4.
5
(N
=
57
)
20
.9
C
au
da
l
le
n
gt
h
5.
5
4.
9?
6.
7
(N
=
9)
6.
1
7.
9
5.
4?
8.
5
(N
=
14
)
7.
8
8.
2
8.
8?
23
.9
(N
=
57
)
12
.8
P
er
ce
n
t
of
h
ea
d
le
n
gt
h
A
n
u
s
to
an
al
-fi
n
in
se
rt
io
n
27
.6
29
.5
?4
8.
2
(N
=
9)
37
.1
24
.8
14
.4
?2
3.
9
(N
=
14
)
18
.7
25
.1
2.
9?
19
.3
(N
=
57
)
11
.2
P
ec
to
ra
l-
fi
n
le
n
gt
h
35
.7
35
.3
?3
8.
7
(N
=
9)
37
.5
39
.3
35
.5
?4
1.
3
(N
=
14
)
38
.6
39
.5
31
.3
?4
6.
9
(N
=
57
)
39
.0
H
ea
d
de
pt
h
at
ey
e
31
.0
27
.9
?3
3.
2
(N
=
9)
30
.1
33
.3
18
.2
?3
6.
5
(N
=
14
)
29
.1
24
.4
23
.3
?3
1.
1
(N
=
10
)
26
.5
H
ea
d
de
pt
h
at
n
ap
e
50
.5
46
.4
?6
0.
7
(N
=
9)
53
.5
53
.9
44
.9
?5
7.
7
(N
=
14
)
49
.2
46
.6
45
.4
?6
0.
3
(N
=
57
)
50
.9
H
ea
d
w
id
th
24
.8
22
.9
?2
7.
6
(N
=
9)
25
.1
28
.4
15
.6
?2
8.
4
(N
=
14
)
22
.7
19
.1
18
.1
?2
3.
5
(N
=
10
)
20
.7
S
n
ou
t
le
n
gt
h
54
.7
51
.8
?5
5.
6
(N
=
9)
54
.0
63
.8
59
.8
?6
5.
7
(N
=
14
)
62
.4
58
.3
44
.3
?6
1.
3
(N
=
57
)
54
.6
P
os
te
ri
or
n
ar
is
to
sn
ou
t
10
.0
8.
7?
10
.5
(N
=
9)
9.
6
53
.4
41
.1
?5
8.
4
(N
=
14
)
50
.9
8.
1
6.
4?
9.
1
(N
=
10
)
8.
0
P
os
te
ri
or
n
ar
is
to
ey
e
44
.6
42
.6
?4
5.
5
(N
=
9)
44
.4
55
.8
53
.9
?5
7.
9
(N
=
14
)
56
.1
61
.8
29
.2
?7
7.
2
(N
=
57
)
56
.4
M
ou
th
le
n
gt
h
9.
1
8.
0?
9.
7
(N
=
9)
8.
9
7.
3
5.
7?
7.
8
(N
=
14
)
6.
7
7.
1
5.
6?
12
.4
(N
=
57
)
8.
0
In
te
rn
ar
ia
l
di
st
an
ce
3.
9
2.
5?
4.
2
(N
=
9)
3.
7
2.
7
2.
5?
3.
6
(N
=
14
)
3.
1
3.
7
3.
0?
6.
4
(N
=
57
)
4.
3
E
ye
di
am
et
er
2.
9
2.
6?
3.
5
(N
=
9)
3.
0
3.
6
2.
9?
4.
6
(N
=
14
)
3.
9
6.
3
4.
1?
10
.5
(N
=
57
)
6.
7
In
te
ro
cu
la
r
w
id
th
5.
4
5.
0?
6.
6
(N
=
9)
5.
90
6.
2
4.
1?
7.
9
(N
=
14
)
6.
3
6.
1
7.
0?
19
.7
(N
=
57
)
10
.0
P
os
to
cu
la
r
di
st
an
ce
47
.3
46
.1
?4
9.
3
(N
=
9)
47
.8
42
.7
40
.0
?4
5.
9
(N
=
14
)
43
.7
42
.2
37
.1
?5
3.
9
(N
=
57
)
45
.4
B
ra
n
ch
ia
l
op
en
in
g
15
.8
11
.2
?1
6.
9
(N
=
9)
15
.2
15
.5
12
.1
?1
7.
9
(N
=
14
)
16
.3
13
.1
11
.8
?2
5.
2
(N
=
57
)
15
.6
P
er
ce
n
t
of
ca
u
da
l
le
n
gt
h
T
ai
l
de
pt
h
33
.0
25
.9
?3
5.
7
(N
=
9)
30
.7
22
.3
18
.9
?2
5.
9
(N
=
10
)
22
.2
17
.6
8.
7?
21
.3
(N
=
57
)
15
.3
C
au
da
l-
fi
n
le
n
gt
h
58
.7
49
.7
?6
2.
5
(N
=
9)
54
.1
37
.1
33
.3
?4
6.
4
(N
=
10
)
39
.4
38
.2
17
.2
?3
8.
9
(N
=
57
)
28
.6
H
,
h
ol
ot
yp
e;
ra
n
ge
in
cl
u
de
s
n
on
ty
pe
sp
ec
im
en
s.
N
u
m
be
r
of
sp
ec
im
en
s
in
di
ca
te
d
in
pa
re
n
th
es
es
.
282 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Sternarchorhynchus britskii Campos-da-Paz, 2000:
529, fig. 9 [type locality: Brazil, Mato Grosso do Sul,
Rio Paran? at Ilha Solteira dam (right margin),
approximately 20?30?S 51?00?W]. ? Albert, 2003: 500
[in listing of members of genus]. ? Campos-da-Paz,
2005: 399 [additional locality information; threatened
status]. ? Triques, 2007: 125 [threatened status]. ? da
Gra?a & Pavanelli, 2007: 193, unnumbered fig.
[Brazil, upper Rio Paran?; threatened status]. ?
Crampton, 2007: 289 [Brazil, Rio Paran?].
Diagnosis: Sternarchorhynchus britskii is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the hyaline anal fin, the presence of a definite
series of scales along the mid-dorsal region of the body,
the lateral line that extends to the base of the caudal
fin, the possession of five branchiostegal rays, seven
teeth on the premaxilla, eight teeth in the outer row of
the dentary, two teeth in the inner row of dentary, 15
precaudal vertebrae, 16?22 anterior unbranched anal-
fin rays, 166?178 total anal-fin rays, 11?15 branched
pectoral-fin rays, 13?15 caudal-fin rays, 16?17 precau-
dal vertebrae, 11?13 scales above the lateral line at the
midbody, the greatest body depth (12.1?15.7% of LEA),
the length of the base of the anal fin (86.4?93.0% of
LEA), the prepectoral-fin distance (19.4?23.6% of
LEA), the preanal distance (12.2?15.8% of LEA), the
distance from the anus to the anal-fin insertion (14.4?
24.8% of HL), the head length (18.9?23.9% of LEA), the
snout length (59.8?65.7% of HL), the eye diameter
(2.9?4.6% of HL), the distance from the posterior naris
to the eye (53.9?57.9% of HL), the head depth at the
nape (44.9?57.7% of HL), the caudal length (5.4?8.5%
of HL), the mouth length (5.7?7.8% of HL), the pos-
tocular distance (40.0?45.9% of HL), the pectoral-fin
length (35.5?46.4% of HL), the caudal-fin length (33.3?
45.8% of caudal length), and the tail depth (18.9?25.9%
of caudal length).
Diagnosis: Morphometric data for examined speci-
mens in Table 4.
Lateral line extending posteriorly to point between
two scales short of base of caudal fin, but absent on
fin. Snout elongate, compressed and curved ventrally
anteriorly. Sexual dimorphism in form of lower jaw
and associated dentition found in many congeners not
apparent in examined samples. Anus and urogenital
papilla located ventral to head. Openings shift ante-
riorly ontogenetically, with larger specimens having
those structures situated along vertical three orbital
diameters anterior of vertical through anterior
margin of eye. Combined opening for anus and uro-
genital papilla longitudinally ovoid.
Premaxilla with seven teeth apparent in whole
specimens (N = 1). Dentary with two tooth rows pos-
teriorly and one sometimes somewhat irregular row
anteriorly in whole specimens. Teeth in outer row
eight and in inner row two (N = 1). Mouth small and
terminal, rictus situated anterior of vertical through
anterior naris.
Branchiostegal rays five; with first and second rays
narrow and third to fifth rays large and broad. Pre-
caudal vertebrae 16?17 (13?14 anterior; three transi-
tional; N = 5).
Pectoral-fin rays ii + 11?13 [ii + 13] (N = 13). Anal-
fin origin located anterior to opercle. Anterior
unbranched anal-fin rays 16?22 [19] (N = 13). Total
anal-fin rays 166?178 [173] (N = 13). Scales above
lateral line at midbody 11?13 [13] (N = 13). Scales
present along mid-dorsal line in region anterior to
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located on
posterior half of body, approximately at 70% of TL.
Filament extending to within region delimited by
verticals through point one scale short of vertical
through posterior terminus of base of anal fin or point
slightly beyond terminus of the base of that fin. Tail
compressed and short, ending in small, elongate,
slightly pointed caudal fin. Caudal-fin rays 13?15 [14]
(N = 13).
Coloration in alcohol: Overall ground coloration
ranging from light brown up to grey to brown. Head
with anteriorly attenuating band of more concen-
trated dark chromatophores along dorsolateral region
of snout in region from eye to vertical through poste-
rior naris. Dark pigmentation on snout forms lateral
border of narrow, lightly coloured, mid-dorsal stripe
extending from snout to rear of head and widening
Figure 29. Sternarchorhynchus britskii, holotype, 272 mm total length, MZUSP 52923; Brazil, Mato Grosso do Sul, Rio
Paran?.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 283
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
slightly laterally along postocular portion of head
(stripe indistinct, particularly in postocular region in
some specimens). Remainder of head light brown
other than for lightly coloured region forming anteri-
orly convex arch overlying preopercle in some indi-
viduals. Body pigmentation darker dorsally, but with
irregular and to varying degrees obscure, narrow,
more lightly coloured mid-dorsal region. Stripe some-
times continuous anteriorly with mid-dorsal stripe on
head and extending posteriorly in some specimens to
origin of electroreceptive filament. Pectoral fin with
dark chromatophores distributed over rays and oth-
erwise hyaline. Anal fin lightly coloured overall, with
small dark chromatophores overlying rays. Caudal fin
with dusky central basal spot in some individuals but
otherwise hyaline over rays.
Distribution: Sternarchorhynchus britskii is only
known from the upper R?o Paran? basin in the states
of Mato Grosso do Sul, Minas Gerais, and S?o Paulo,
Brazil (Fig. 28).
Secondary sexual dimorphism: Sternarchorhynchus
britskii is not known to demonstrate sexual
dimorphism.
Remarks: Britski (1972: 91) reported that S. britskii
(identified therein as Sternarchorhynchus sp.) was
rare in sampled habitats with the type series having
been collected in a cofferdam during the building of
the Ilha da Solteira hydroelectric dam across the
upper Rio Paran?. More recently, Campos-da-Paz
(2005: 399) proposed that the insect larvae utilized by
S. britskii may be associated with a specific habitat in
flowing deep river channels. The extensive modifica-
tions of the upper Rio Paran? associated with the
construction of major impoundments along the length
of the main river channels throughout the basin and
the resultant destruction of flowing deep river habi-
tats favoured by S. britskii has undoubtedly adversely
affected many populations of the species. As a conse-
quence, S. britskii is now listed as threatened
(Campos-da-Paz, 2005; Triques, 2007).
Material examined
BRAZIL. Mato Grosso do Sul: Rio Paran?, at Ilha
Solteira dam, cofferdam at right margin of river
(approximately 20?30?S, 51?00?W), MZUSP 24468
52923, 1 (262; holotype); MZUSP 24464, 8 [163?254;
six specimens from this lot designated as paratypes
by Campos-da-Paz (2000), but not possible to now
determine which specimens were so designated];
MBUCV 13398, 1 (244; formerly MZUSP 24464, in
part; nontype specimen collected with holotype). Rio
Paran?, Ilha Solteira (approximately 20?30?S,
51?00?W), MZUSP 23097, 3 (125?240). Rio Paran?,
ROM 37960, 1 (210). S?o Paulo: Rio Grande, Represa
de ?gua Vermelha along boundary between state of
S?o Paulo and Minas Gerais, MZUSP 39956, 7 (128?
232). Fernand?polis (approximately 20?15?36?S,
50?13?59?W), MZUSP 50188, 1 (265).
STERNARCHORHYNCHUS CABOCLO DE SANTANA &
NOGUEIRA (FIGS 28, 30; TABLE 4)
Sternarchorhynchus oxyrhynchus, not of M?ller &
Troschel, Ferreira, dos Santos & J?gu, 1988: 344 [in
listing of species from Rio Mucaja? in vicinity of Ilha
Pared?o, Roraima, Brazil].
Sternarchorhynchus caboclo de Santana &
Nogueira, 2006: 89: figs 1b, 2b, c [type locality:
Brazil, Roraima, Rio Mucaja?, below Cachoeira
Pared?o].
Diagnosis: Sternarchorhynchus caboclo is distin-
guished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical
through anterior nares, the presence of a definite
series of scales along the mid-dorsal region of the
body, the absence of a more lightly coloured narrow
band of mid-dorsal pigmentation on the head and
mid-dorsal region of the body anterior of the origin
of the electroreceptive filament, the lateral line that
extends posteriorly to the base of the caudal fin, the
dusky anal fin, the possession of four branchiostegal
rays, six premaxillary teeth, 13?15 branched
pectoral-fin rays, 153?174 total anal-fin rays, ten to
12 scales above the lateral line at the midbody, the
greatest body depth (11.0?14.7% of LEA), the length
of the base of the anal fin (79.3?86.4% of LEA), the
mouth length (5.6?12.4% of HL), the snout length
(44.3?61.3% of HL), the head depth at the nape
Figure 30. Sternarchorhynchus caboclo, holotype, male, 225 mm total length, INPA 22894; Brazil, Roraima, Rio Mucaja?.
284 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
(45.4?60.3% of HL), the internarial distance (3.0?
6.4% of HL), the eye diameter (4.1?10.5% of HL),
the pectoral-fin length (31.3?46.9% of HL), the
interocular distance (6.1?19.7% of HL), and the
caudal-fin length (17.2?38.9% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 4.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
ranging from nearly straight to slightly curved ven-
trally. Mouth terminal and relatively small, with
rictus located slightly anterior to, or along, vertical
through anterior naris. Anus and urogenital papilla
located ventral to head, with their position apparently
somewhat ontogenetically variable in available
sample. Anus and urogenital papilla in smaller indi-
viduals located along vertical slightly less than one
orbital diameter posterior of rear margin of eye and
very slightly anterior of vertical through anterior
margin of eye in larger individuals. Combined
opening for anus and urogenital papilla longitudi-
nally ovoid in all specimens.
Premaxilla with eight to ten teeth (N = 8) apparent
in whole specimens. Dentary with two tooth rows;
outer row with seven to eight teeth and inner row
with three to four teeth (N = 7).
Branchiostegal rays four; with first two rays
narrow and elongate and fourth and fifth rays large
and broad and posteriorly forked (de Santana &
Nogueira, 2006: fig. 3). Precaudal vertebrae 16 (13?14
anterior; two to three transitional; N = 18).
Pectoral-fin rays ii + 13?15 [ii + 13] (N = 58). Anal-
fin origin located anterior to vertical through margin
of opercle. Anterior unbranched anal-fin rays 20?40
[23] (N = 58). Total anal-fin rays 153?174 [168]
(N = 58). Scales above lateral line at midbody 10?12
[10] (N = 58). Scales present along mid-dorsal line to
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located rela-
tively far posteriorly, approximately at 67% of TL.
Filament extending posteriorly to point two to four
scales beyond vertical through posterior terminus of
base of anal fin. Tail compressed and moderate,
ending in small, elongate caudal fin. Caudal-fin rays
12?15 [12] (N = 33).
Coloration in alcohol: Overall coloration dark brown.
Head dark overall with stripe of slightly darker pig-
mentation extending anteriorly from orbit to, or
nearly to, tip of snout. Slightly more lightly coloured
region present on lateral surface of anterior one-
third to one-half of snout. Ventral margin of snout
dark. Mid-dorsal region of head dark. Body dark
brown overall with mid-dorsal region uniformly
dark. Pectoral fin dusky with rays covered with
small dark chromatophores. Anal fin dusky with
rays overlain by small, dark chromatophores. Basal
portions of caudal fin dusky, but with distal portions
of fin hyaline.
Distribution: Sternarchorhynchus caboclo is only
known from the Rio Mucaja? basin of Roraima, Brazil
(Fig. 28).
Ecology: The types of S. caboclo were collected above
and below a waterfall along the Rio Mucaja?. Accord-
ing to Ferreira et al. (1988: 341) the river in that
region is characterized by steep banks and with dense
forest along the shore. Large amounts of aquatic
plans of the family Podostemonacease were present in
the area, with the water being acidic (pH 5.8) and
well oxygenated (91% saturation).
Secondary sexual dimorphism: de Santana &
Nogueira (2006: 90: fig. 2b, c) noted apparent differ-
ences in the angle of the snout and depth of the
posterior portion of the snout in males versus females
of S. caboclo. A definitive statement on the generality
of this difference requires examination of more exten-
sive samples of the species.
Remarks: Sternarchorhynchus caboclo and S. severii
were collected at the type location. The two
species are readily distinguishable by the number of
branchiostegal rays (four versus five, respectively),
pigmentation of the mid-dorsal region of the
head and body (head and body dark versus with
narrow, lightly coloured stripe extending post-
eriorly to the origin of the electroreceptive filament,
respectively), the pectoral-fin length (31.3?46.9
versus 48.7?66.6% of HL, respectively), and the
depth at the eye (23.3?31.1 versus 31.7?36.0% of
HL, respectively).
Material examined
BRAZIL. Roraima: Rio Branco basin, Rio Mucaja?,
below Cachoeira Pared?o 2 (approximately 2?57?N,
61?27?W), INPA 22894, 1 (225.0, holotype, male);
INPA 10594, 60 (46.3?226, 2 CS specimens,
paratypes). Rio Branco basin, Rio Mucaja?, above
Cachoeira Pared?o 2 (approximately 2?57?N,
61?27?W), INPA 10578, 1 (178, paratype). Rio Branco
basin, Rio Mucaja?, Estrada between F? and Esper-
an?a, INPA 10592, 2 (156?160, paratypes). Rio Branco
basin, side channel of Rio Mucaja?, INPA 10541, 1
(36). Rio Branco basin, Rio Mucaja?, approximately
2 km from Cachoeira Pared?o 2, mouth of tributary
igarap? (approximately 2?57?N, 61?27?W); INPA
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 285
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
10580, 1 (193). Rio Branco basin, mouth of Igarap?
Tra?ra, INPA 10590, 1 (200).
STERNARCHORHYNCHUS CHAOI SP. NOV.
(FIGS 28, 31; TABLE 5)
Diagnosis: Sternarchorhynchus chaoi is distin-
guished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical
through anterior nares, the absence of scales along
the mid-dorsal region of the body as far posteriorly
as the vertical through posterior limit of the pecto-
ral fin, the presence of a more lightly coloured
narrow band of mid-dorsal pigmentation on the
head and mid-dorsal region of the body that extends
posteriorly to the origin of the electroreceptive fila-
ment and sometimes beyond that point, the pres-
ence of eight to 13 premaxillary teeth, 15 precaudal
vertebrae, 15?23 anterior unbranched anal-fin rays,
165?178 total anal-fin rays, and ten to 13 scales
above the lateral line at the midbody, the greatest
body depth (10.0?11.7% of LEA), the eye diameter
(3.0?4.2% of HL), the head width (19.5?23.1% of
SL), the postocular distance (39.1?41.3% of HL), and
the caudal length (5.7?8.9% of LEA).
Description: Morphometric data for examined speci-
mens in Table 5.
Lateral line extending posteriorly to point approxi-
mately three scales short of base of caudal fin and
absent on remainder of tail and fin. Snout elongate,
compressed and nearly straight to slightly curved
ventrally distally. Mouth terminal and relatively
small, with rictus located within area delimited by
verticals running slightly anterior to and slightly
posterior of anterior naris. Anus and urogenital
papilla located ventral to head, with their position
somewhat ontogenetically variable in available
sample. Anus and urogenital papilla located along
vertical approximately three orbital diameters poste-
rior of rear margin of eye in smaller specimens and
very slightly posterior of, or along, vertical through
eye in larger individuals. Combined opening for anus
and urogenital papilla ovoid in one apparent female
and somewhat more horizontally elongate in juveniles
and apparent males.
Premaxilla with eight to 13 teeth (N = 11) apparent
in whole specimens. Dentary with two tooth rows;
outer row with seven to nine teeth and inner row with
three to five teeth (N = 11).
Branchiostegal rays five; with first three rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15 (12 anterior; three
transitional; N = 11).
Pectoral-fin rays ii + 11?13 [13] (N = 11). Anal-fin
origin located anterior to vertical through margin of
opercle. Anterior unbranched anal-fin rays 15?23 [22]
(N = 10). Total anal-fin rays 165?178 [176] (N = 10).
Scales above lateral line at midbody 10?13 [12]
(N = 11). Scales absent along mid-dorsal line for dis-
tance of one-quarter to one-third of distance between
rear of head and origin of midsaggital electroreceptive
filament. Origin of midsaggital electroreceptive fila-
ment located approximately at 67% of TL. Filament
extending posteriorly to vertical through posterior
terminus of base of anal fin or one to two scales
beyond that point. Tail compressed and short, ending
in small, moderate, lanceolate caudal fin. Caudal-fin
rays 13?16 [14] (N = 8).
Coloration in alcohol: Overall coloration dark brown.
Snout dark overall with stripe of darker pigmentation
extending anteriorly from orbit for distance one-half
to two-thirds length of snout. Dorsal region of dark
pigmentation on head forms lateral margin of narrow,
Figure 31. Sternarchorhynchus chaoi sp. nov., holotype, presumably male, 155 mm total length, INPA 28357; Brazil,
Rond?nia, Rio Jamari.
286 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
T
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=
3)
12
.8
P
ec
to
ra
l-
fi
n
le
n
gt
h
34
.5
27
.5
?3
8.
3
(N
=
10
)
34
.4
42
.4
38
.0
?4
6.
5
(N
=
14
)
42
.9
34
.5
36
.9
?3
7.
8
(N
=
3)
37
.3
H
ea
d
de
pt
h
at
ey
e
25
.9
25
.0
?3
2.
0
(N
=
10
)
27
.8
27
.9
25
.6
?3
5.
4
(N
=
14
)
30
.3
?
25
.6
?3
0.
3
(N
=
2)
28
.0
H
ea
d
de
pt
h
at
n
ap
e
47
.7
41
.4
?4
6.
6
(N
=
10
)
44
.3
51
.3
46
.2
?5
8.
8
(N
=
14
)
51
.9
41
.8
42
.8
?4
8.
3
(N
=
3)
45
.2
H
ea
d
w
id
th
20
.6
19
.5
?2
3.
1
(N
=
10
)
20
.9
23
.6
21
.3
?2
5.
9
(N
=
14
)
23
.4
?
19
.0
?1
9.
8
(N
=
2)
19
.5
S
n
ou
t
le
n
gt
h
60
.1
58
.8
?6
2.
9
(N
=
10
)
60
.9
66
.3
60
.6
?6
7.
0
(N
=
14
)
64
.8
60
.2
60
.6
?6
2.
5
(N
=
3)
61
.8
P
os
te
ri
or
n
ar
is
to
sn
ou
t
8.
1
7.
2?
9.
1
(N
=
10
)
8.
4
6.
8
6.
0?
8.
5
(N
=
14
)
7.
6
?
5.
9?
6.
2
(N
=
2)
6.
0
P
os
te
ri
or
n
ar
is
to
ey
e
50
.0
46
.3
?5
2.
1
(N
=
10
)
50
.1
57
.6
50
.9
?5
9.
3
(N
=
14
)
55
.7
?
54
.9
?5
9.
8
(N
=
2)
57
.4
M
ou
th
le
n
gt
h
5.
6
5.
5?
6.
7
(N
=
10
)
6.
1
5.
5
5.
2?
8.
8
(N
=
14
)
6.
5
5.
3
3.
5?
5.
6
(N
=
3)
4.
2
In
te
rn
ar
ia
l
di
st
an
ce
3.
3
2.
5?
3.
6
(N
=
10
)
2.
9
3.
2
2.
3?
4.
0
(N
=
14
)
3.
2
2.
8
2.
4?
2.
6
(N
=
3)
2.
5
E
ye
di
am
et
er
3.
4
3.
0?
4.
2
(N
=
10
)
3.
5
2.
6
2.
5?
4.
2
(N
=
14
)
3.
1
3.
9
4.
1?
5.
0
(N
=
3)
4.
7
In
te
ro
cu
la
r
w
id
th
6.
4
5.
5?
7.
2
(N
=
10
)
6.
5
6.
1
5.
2?
8.
5
(N
=
14
)
6.
0
6.
5
4.
8?
6.
4
(N
=
3)
5.
5
P
os
to
cu
la
r
di
st
an
ce
40
.3
39
.4
?4
1.
3
(N
=
10
)
40
.5
39
.3
37
.4
?4
3.
7
(N
=
14
)
41
.0
36
.9
33
.6
?3
9.
2
(N
=
3)
37
.2
B
ra
n
ch
ia
l
op
en
in
g
12
.7
10
.0
?1
4.
8
(N
=
10
)
12
.2
15
.4
11
.7
?1
7.
7
(N
=
14
)
14
.6
11
.8
11
.7
?1
2.
9
(N
=
3)
12
.1
P
er
ce
n
t
of
ca
u
da
l
le
n
gt
h
T
ai
l
de
pt
h
34
.2
14
.0
?2
1.
8
(N
=
8)
16
.6
25
.3
23
.6
?2
9.
6
(N
=
12
)
26
.9
11
.9
10
.6
?1
1.
7
(N
=
2)
11
.1
C
au
da
l-
fi
n
le
n
gt
h
69
.5
29
.6
?5
1.
3
(N
=
8)
36
.4
35
.5
30
.9
?6
1.
4
(N
=
12
)
40
.9
24
.3
19
.5
?2
5.
2
(N
=
2)
22
.3
N
u
m
be
r
of
sp
ec
im
en
s
in
di
ca
te
d
in
pa
re
n
th
es
es
.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 287
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
somewhat obscure, lightly coloured mid-dorsal stripe.
Stripe expands very slightly laterally over postocular
region, but separated from lightly coloured mid-dorsal
stripe on body by region of dark pigmentation. Mid-
dorsal lightly coloured stripe on body commences
somewhat posterior of terminus of comparable stripe
on head and extends varying degrees posteriorly,
reaching to origin of electroreceptive filament in some
individuals. Pectoral fin distinctly dusky with rays
covered with small, dark chromatophores. Anal fin
dusky with rays overlain by small, dark chromato-
phores. Basal portions of caudal fin dusky to dis-
tinctly dark, but with distal portions of fin hyaline.
Distribution: Sternarchorhynchus chaoi is only known
from one locality in the Rio Jamari basin of the state
of Rond?nia, Brazil (Fig. 28).
Secondary sexual dimorphism: No clear sexual dimor-
phism is apparent in the limited available samples of
S. chaoi.
Etymology: The species name, chaoi, is in honour of
Ning Labish Chao of the Universidade Federal do
Amazonas, who provided invaluable assistance and
financial support to the first author during his studies
of gymnotiforms in Manaus, Brazil.
Material examined
Holotype: ? BRAZIL. Rond?nia: Rio Jamari, Porto
Velho, canal de desvio da (diversion canal of ) UHE
(Usina Hidroel?ctica) Samuel (approximately 8?27?S,
63?30?W), collected by G. M. dos Santos, 7.vi.1998;
INPA 28357 (155).
Paratypes: ? BRAZIL. Rond?nia: Rio Jamari, Porto
Velho, Canal de desvio da (diversion canal of) UHE
(Usina Hidroel?ctica) Samuel (approximately 8?27?S,
63?30?W), collected with holotype by G. M. dos Santos,
7.vi.1998; INPA 20851, 11 (126?174); USNM 391713,
1 (164).
Nontype specimens: ? BRAZIL. Rond?nia: amongst
rocks above UHE (Usina Hidroel?ctrica) Samuel
(approximately 8?27?S, 63?30?W); INPA uncat., field
number Polo 896, 7 (48?168).
STERNARCHORHYNCHUS CRAMPTONI SP. NOV.
(FIGS 28, 32, 33; TABLE 5)
Sternarchorhynchus cf. roseni, Rapp Py-Daniel &
Cox-Fernandes, 2005: 105, fig. 5. [Brazil, Amazon
Basin; secondary sexual dimorphics in form of lower
jaw].
Diagnosis: Sternarchorhynchus cramptoni is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the presence of a definite series of scales along
the mid-dorsal region of the body, the presence of a
more lightly coloured narrow band of mid-dorsal pig-
mentation on the head and mid-dorsal region of the
body anterior of the origin of the electroreceptive
filament and sometimes beyond that point, the pres-
ence of a dark band along the distal one-fifth to
one-half of much of the anal fin and over most of the
posterior rays of that fin, the presence of eight to 12
Figure 32. Sternarchorhynchus cramptoni sp. nov., holotype, female, 290 mm total length, INPA 28376; Brazil,
Amazonas, Rio Solim?es, downstream from mouth of Rio Purus.
Figure 33. Sternarchorhynchus cramptoni sp. nov., sexually dimorphic male demonstrating modifications of dentary
and dentary dentition, 331 mm total length, MCP 41638, demonstrating expanded sexually dimorphic dentary and
associated dentition; Brazil, Amazonas, Rio Solim?es, Ilha do Prego.
288 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
teeth on the premaxilla, six to eight teeth on the outer
tooth row of the dentary, 180?221 total anal-fin-rays,
16 precaudal vertebrae, the preanal distance (10.9?
14.9 of LEA), the greatest body depth (9.7?12.1% of
LEA), the caudal length (5.0?8.4% of LEA), the head
length (16.0?19.5% of LEA), the distance from the
anus to the anal-fin insertion (6.7?12.3% of HL), the
snout length (60.6?67.0% of HL), the head depth at
the nape (46.2?58.8% of HL), the postocular distance
(37.4?43.7% of HL), the prepectoral-fin distance
(16.5?20.3% of HL), the tail depth (23.6?29.6% of
caudal length), and the caudal-fin length (30.9?61.4%
of caudal length).
Description: Morphometric data for holotype and
paratypes in Table 5.
Lateral line extending to base of caudal fin, but
absent on fin. Snout elongate, compressed and
curved ventrally distally. Posterior naris located
closer to tip of snout than to anterior margin of eye.
Branchial opening restricted and situated slightly
anterior to vertical through pectoral-fin origin. Loca-
tion of anus and urogenital papilla ontogenetically
variable and apparently sexually dimorphic. Anus
and urogenital opening in smaller individuals posi-
tioned along vertical located slight distance poste-
rior of vertical through rear margin of eye. Larger
specimens lacking secondary male characters with
two openings located at vertical running slightly
anterior of anterior margin of eye. Males with patch
of large teeth at anterior of expanded dentary
with anus and urogenital papilla positioned more
anteriorly at vertical about one-third of distance
between anterior margin of eye and tip of snout.
Aperture for anus and urogenital opening
rounded in juveniles and apparent females; longitu-
dinally elongate in males demonstrating sexually
dimorphic modifications of dentary and associated
dentition.
Premaxilla of small size, somewhat rounded, with
eight to 12 teeth (N = 6). Dentary elongate with fleshy
pad on anteroventral surface in larger specimens.
Dentaries approximately of same length in males and
females, but with form sexually dimorphic. Anterior
portion of dentary of males somewhat widened later-
ally into moderately dorsally bulbous structure
bearing enlarged teeth (degree of expansion of
dentary and of enlargement of teeth less pronounced
than that present in some congeners). Dentary with
two rows of curved conical teeth. Outer row with six
to eight teeth (N = 10) and inner row with three to
four teeth (N = 8). Mouth terminal with rictus located
anterior to vertical through posterior naris in juve-
niles. Rictus slightly more posteriorly positioned in
larger individuals.
Branchiostegal rays five; with first to third rays
relatively narrow and elongate and remaining rays
large and broad. Precaudal vertebrae 16 (12?13 ante-
rior; three to four transitional, N = 11).
Pectoral-fin rays ii + 11?14 [ii + 14] (N = 30). Anal-
fin origin located slightly posterior of vertical through
anterior margin of opercle. Anterior unbranched anal-
fin rays 17?29 [24] (N = 15). Total anal-fin rays 180?
221 [221] (N = 24); number of rays apparently
increases ontogenetically given evident correlation
between greater body size and increased numbers of
anal-fin rays amongst examined specimens. Scales
above lateral line at midbody 9?12 [9] (N = 33). Scales
along mid-dorsal region of body readily apparent.
Origin of midsaggital electroreceptive filament
located approximately at 62% of TL. Filament extend-
ing posteriorly to vertical running through to poste-
rior terminus of base of anal fin. Tail compressed and
short, ending in small, caudal fin with rounded distal
margin. Caudal-fin rays 13?16 [15] (N = 21).
Coloration in life: A photo of a recently collected
specimen of S. cramptoni from the Rio Negro, Brazil,
shows a whitish-pink fish with the dark chromato-
phores on the head appearing as very small dots.
Coloration in alcohol: Overall ground coloration
ranging from brown to dark brown. Head and body
with dark chromatophores relatively densely scat-
tered over surfaces. Size of chromatophores and
intensity of their pigmentation greater in overall
darker specimens. Snout with variably distinct,
narrow band of darker pigmentation extending ante-
riorly from region somewhat anterior of eye and
reaching anterior portion of snout in many specimens.
Band of dark pigmentation forms lateral border of
narrow, lightly coloured mid-dorsal band on head.
Ventral margin of snout somewhat darker than
lateral surface of that region in some specimens, more
so in individuals with overall dark coloration of head
and body. Mid-dorsal region of head with narrow,
lightly coloured stripe apparent even in overall darkly
pigmented individuals. Head stripe continuous poste-
riorly with narrow, lightly coloured mid-dorsal stripe
on body. Body pigmentation slightly darker dorsally,
but with lightly pigmented mid-dorsal stripe extend-
ing posteriorly onto basal portions of electroreceptive
filament and to varying degrees posteriorly from that
point in different individuals.
Pectoral-fin coloration ranging from dusky to dis-
tinctly dark, with dark pigmentation overlying
pectoral-fin rays and more developed distally. Anal
fin with distinct band of dark pigmentation. Dark
band covering approximately distal one-fifth to one-
half of fin in most examined specimens, but with
dark coloration extending over all, or nearly all, of
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 289
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
lateral surface of fin in some darkly coloured indi-
viduals. Caudal-fin rays ranging from slightly dusky
to distinctly dark with extent and intensity of pig-
mentation greater in overall more darkly pigmented
individuals.
Distribution: Sternarchorhynchus cramptoni is widely
distributed along the mainstream of the Amazon
River from the region of Iquitos in north-eastern Peru
downstream to the Rio Trombetas, a left bank tribu-
tary of the Amazon in the state of Par?, Brazil
(Fig. 28).
Ecology: Juveniles of S. cramptoni have been cap-
tured along the margins of main river channels in
v?rzea, whereas adults were captured in the main
channels of the sampled rivers (C. D. de Santana,
pers. observ.).
Electrical organ discharge: Crampton & Albert
(2006: 689) reported that S. cramptoni (the Sterna-
rchorhynchus n. sp. C of those authors and Cramp-
ton, 2007) has a complex EOD pattern comprising
four phases of alternating polarities with the weak
negative phase apparently flat, but on closer exami-
nation exhibiting a gentle curve around a single
peak (the type F EOD of those authors). They also
noted that the multiphasic nature of this EOD form
diverts the energy of the signal away from the fun-
damental, with the first harmonic representing the
peak power frequency.
Secondary sexual dimorphism: Examined samples of
S. cramptoni demonstrated sexual dimorphism in the
form of the lower jaw and associated dentition.
Although males of the species have a somewhat
enlarged anterior portion of the dentary, that region is
not as relatively elongate or bulbous as in males of
some congeners. Dentary dentition in that region is
also proportionally less developed than are the teeth in
mature males of many species of Sternarchorhynchus.
Etymology: The species name, cramptoni, is in recog-
nition of the many contributions of William Cramp-
ton, University of Central Florida, to our knowledge
of the biology and systematics of gymnotiforms.
Material examined
Holotype: ? BRAZIL. Amazonas: Rio Solim?es, down-
stream from mouth of R?o Purus (3?27?27?S,
60?45?26?W); collected by Angela Zanata et al.,
1.viii.1996; INPA 28376 (290, female; formerly FMNH
115489).
Paratypes: ? BRAZIL. Amazonas: Rio Solim?es, south
bank of Ilha do Jaraqui, Alvar?es (3?09.51?S,
64?48.76?W), collected by W. G. R. Crampton,
9.xii.1999; MCP 41637, 1 (236). R?o Solim?es, Ilha do
Prego, opposite town of Alvar?es (3?12.63?S
64?47.38?W); collected by W. G. R. Crampton,
19.ii.2001; MCP 41638, 1 (331). Rio Solim?es, down-
stream from mouth of Rio Purus (3?27?27?S,
60?45?26?W); collected by Angela Zanata et al.,
1.viii.1996, collected with holotype, FMNH 115489, 3
(155?273). Rio Solim?es, downstream from mouth of
R?o Purus (3?26?46?S, 60?45?00?W); collected by
Angela Zanata et al., 31.vii.1996; FMNH 115488, 4
(231?275). Rio Solim?es, downstream from mouth of
Rio Purus (3?27?22?S, 60?45?21?W); collected by
Angela Zanata et al., 1.viii.1996; FMNH 115490, 7
(133?315).
Nontype specimens: ? BRAZIL. Amazonas: Rio
Solim?es, between mouths of Rio I?a and R?o
Tonantins, between towns of S?o Ant?nio do I?a and
Nova Tonantins (2?55?00?S, 67?50?48?W); FMNH
115483, 1 (222). Rio Solim?es, between mouth of Rio
I?a and R?o Tonantins, between towns of S?o Ant?nio
do I?a and Nova Tonantins (2?55?24?S, 67?51?23?W);
FMNH 115482, 1 (280). Rio Amazonas, between mouth
of Rio Madeira and Paran? do Serpa, between Manaus
and Itacoatiara (3?19?44?S, 58?35?28?W); FMNH
115494, 1 (128). Rio Amazonas, downstream from
mouth of Rio Madeira, upstream from Itacoatiara
(3?20?22?S, 58?36?31?W); FMNH 115496, 1 (267). Rio
Amazonas, upstream from mouth of Rio Madeira and
upstream from Itacoatiara (3?15?42?S, 58?58?24?W);
FMNH 115491, 2 (154?293). R?o Amazonas, down-
stream from mouth of R?o Madeira and upstream from
Itacoatiara (3?20?09?S, 58?36?11?W); FMNH 115492, 1
(240). Rio Amazonas, downstream from mouth of Rio
Madeira, upstream from Itacoatiara (3?20?59?S,
58?39?32?W); FMNH 115495, 1 (307). Rio Amazonas,
between mouths of Rio Negro and Rio Madeira,
between towns of Nova Oriente and Itacoatiara
(3?16?40?S, 58?56?56?W); FMNH 115493, 1 (215). Rio
Purus, Itapuru (4?17?S, 61?54?10?W); INPA 17098, 1
(180). Rio Solim?es, Ilha da Marchantaria; INPA 27491
(255); INPA 27114, 1 (245). Rio Purus, marginal lago on
shore opposite Lago Surara (4?07?47S, 61?34?50?W);
INPA 17099, 1 (265). Rio Purus at Beruri; INPA 17602,
1 (380). Rio Purus, Baia da Resaca, at Beruri; INPA
17603, 2 (328?358). Rio Solim?es, Ilha do Careiro;
INPA 17601, 3 (327?334). Rio Solim?es; INPA uncat. 1
(166). Rio Solim?es (3?36?19?S, 61?18?39?W); USNM
373328, 1 (163). Rio Solim?es, below Purus (3?36?25?S
61?19?40?W); MZUSP 56882, 2 (150?164). Par?: R?o
Trombetas, between tributaries Lago Iripixi and Cach-
oeiri, between towns Oriximin? and Fazenda Para?so;
FMNH 115487, 1 (170).
290 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
PERU. Loreto: Iquitos, R?o Amazonas, obtained
from aquarium trade; UF 116761, 4 (99?121), UF
123454, 2 (167?310). Iquitos, R?o Amazonas; UF
116760, 1 (241).
STERNARCHORHYNCHUS CURUMIM DE SANTANA &
CRAMPTON (FIGS 34, 35; TABLE 5)
Sternarchorhynchus curumim de Santana & Cramp-
ton, 2006: 59, fig. 1 [type locality: Brazil, Amazonas,
Rio Tef?, Toco Preto, Municipality of Tef?, 3?47.31?S,
64?59.91?W]. ? Crampton, 2007: 289, 297 [western
Amazon; occurrence in blackwater but not whitewater
habitats].
Diagnosis: Sternarchorhynchus curumim is distin-
guished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical
Figure 34. Sternarchorhynchus curumim, paratype, female, 211 mm total length, MCP 38305; Brazil, Amazonas, R?o
Tef?.
Figure 35. Map of central and northern South America showing geographical distribution of Sternarchorhynchus
curumim, Sternarchorhynchus curvirostris, Sternarchorhynchus freemani sp. nov. (1 = holotype locality), Sternar-
chorhynchus galibi sp. nov. (2 = holotype locality), and Sternarchorhynchus gnomus (some symbols represent more
than one locality and/or lot of specimens).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 291
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
through anterior nares, the presence of a definite
series of scales along the mid-dorsal region of the
body, the absence of a more lightly coloured narrow
band of mid-dorsal pigmentation on the head and
mid-dorsal region of the body anterior of the origin
of the electroreceptive filament, the lateral line that
extends to the base of the caudal fin, the dusky anal
fin without a distinct dark band along its distal
margin, the possession of seven to ten teeth on the
premaxillary, seven to eight teeth in the outer row
of the dentary, 15 precaudal vertebrae, 23?24 ante-
rior unbranched anal-fin rays, 179?189 total anal-fin
rays, ten to 11 scales above the lateral line at the
midbody, 13?15 caudal-fin rays, the greatest body
depth (9.0?10.0% of LEA), the distance from the
anus to the anal-fin insertion (8.3?13.5% of HL), the
preanal distance (12.4?14.4% of LEA), the caudal
length (10.9?12.2% of LEA), the head length (18.7?
20.6% of LEA), the snout length (60.2?62.5% of HL),
the mouth length (3.5?5.6% of HL), the eye diam-
eter (4.1?5.0% of HL), the internarial distance (2.4?
2.8% of HL), the postocular distance (33.6?39.2% of
HL), the pectoral-fin length (34.5?37.8% of HL), the
tail depth (10.6?11.9% of caudal length), and the
caudal length (10.9?12.2% of LEA).
Description: Morphometric data for examined speci-
mens in Table 5.
Lateral line extending posteriorly to point approxi-
mately at base of caudal fin but absent on fin. Snout
elongate, compressed and slightly curved ventrally
distally. Mouth terminal and relatively small, with
rictus located slightly posterior of vertical through
anterior naris. Anus and urogenital papilla located
ventral to head, with position apparently sexually
dimorphic in limited available sample of species. Anus
and urogenital papilla positioned along vertical situ-
ated approximately one orbital diameter posterior of
rear margin of eye in single examined mature female
and positioned at vertical one orbital diameter ante-
rior of eye in single mature male. Combined opening
for anus and urogenital papilla ovoid in one examined
mature male and somewhat more horizontally elon-
gate in mature female.
Premaxilla with seven to ten teeth (N = 3) apparent
in whole specimens. Dentary with two rows of conical
teeth; outer row with seven to eight teeth and inner
row with three to four teeth (N = 2).
Branchiostegal rays five; with first three rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15 (12 anterior; three
transitional; N = 4).
Pectoral-fin rays ii + 11?12 [ii + 12] (N = 4). Anal-fin
origin located anterior to vertical through margin of
opercle. Anterior unbranched anal-fin rays 23?24
(N = 2). Total anal-fin rays 179?189 [189] (N = 3).
Scales above lateral line at midbody ten to 11 [10]
(N = 4). Scales clearly present along mid-dorsal line to
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located rela-
tively far posteriorly, approximately at 60% of TL.
Filament extending posteriorly to vertical located
approximately three scales posterior of vertical
through terminus of base of anal fin. Tail compressed
and moderate, ending in small, elongate caudal fin.
Caudal-fin rays 13?15 [15] (N = 3).
Coloration in alcohol: Overall coloration of head and
body dark brown. Snout dark overall with stripe of
slightly darker pigmentation extending anteriorly
from orbit to, or nearly to, tip of snout. Pectoral fin
distinctly dusky with rays covered with small dark
chromatophores. Anal fin dusky with rays overlain by
dark chromatophores. Basal portions of caudal fin
distinctly dark, but with distal portions of fin hyaline.
Distribution: Sternarchorhynchus curumim is only
known from one locality in the Rio Tef? in the state of
Amazonas, Brazil (Fig. 35).
Secondary sexual dimorphism: As documented by de
Santana & Crampton (2006: 1166), the single mature
male of S. curumim has the posterior region of the
snout distinctly more developed vertically than do the
three known females. No other sexually dimorphic
features are present other than for the relatively
minor difference in the positions of the anus and
urogenital papilla described above.
Material examined
BRAZIL. Amazonas: Rio Tef?, Toco Preto, Munic?pio
de Tef? (3?47.31?S, 64?59.91?W); MCP 38304, 1 (holo-
type; female, 163 mm); MCP 38305, 2 (paratypes:
female 211 mm, male 183 mm); INPA 25256, 1
(cleared and stained paratype; female, 181 mm).
STERNARCHORHYNCHUS CURVIROSTRIS (BOULENGER)
(FIGS 35, 36, 37; TABLE 6)
Sternarchus (Rhamphosternarchus) curvirostris Bou-
lenger, 1887: 282, pl. 24 [type locality; Ecuador,
Canelos]. ? Eigenmann & Eigenmann, 1891: 62
[assignment to Sternarchorhynchus]. ? Ellis, 1913:
141 [Sternarchorhynchus curvirostris placed in syn-
onymy of S. oxyrhynchus]. ? Fern?ndez-Y?pez, 1967:
18 [Sternarchorhynchus curvirostris resurrected from
synonymy of S. oxyrhynchus]
Sternarchorhynchus curvirostris, Eigenmann &
Bean, 1907: 666 [S. curvirostris as possible synonym
of S. mormyrus]. ? Fern?ndez-Y?pez, 1967: 18 [S.
curvirostris resurrected from synonymy of S. oxyrhyn-
chus]. ? Mago-Leccia, 1994: 37, fig. 55 [as valid
292 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
species in listing of members of genus]. ? Campos-da-
Paz, 2000: 528, fig. 3 [in key to species of Sternarcho-
rhynchus; syntype illustrated]. ? Albert, 2003: 500 [in
listing of members of genus].
Diagnosis: Sternarchorhynchus curvirostris is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the presence of a definite series of scales along
the mid-dorsal region of the body, the lateral line that
extends posteriorly to the base of the caudal fin, the
presence of a more lightly coloured narrow band of
mid-dorsal pigmentation on the head and sometimes
the mid-dorsal region of the body anterior of the origin
of the electroreceptive filament, the darkly coloured
anal fin with darker basal coloration but without a
distinct, dark, distal band, the presence of eight to 11
teeth on the premaxilla, six teeth in the outer row of
the premaxilla, four teeth on the inner row of the
premaxilla, 25 unbranched anal-fin rays, 173?180
total anal-fin rays, 16 precaudal vertebrae, 15?16
caudal-fin rays, the preanal distance (11.3?13.4% of
LEA), the greatest body depth (12.5?15.0% of LEA),
the caudal length (7.9?10.4% of LEA), the distance
from the anus to the anal-fin insertion (6.0?6.8% of
HL), the head depth at the eye (27.2?35.4% of HL), the
head depth at the nape (50.9?67.3% of HL), the snout
length (64.5?66.1% of HL), the distance from the
posterior naris to the snout (6.9?7.4% of HL), the
internarial distance (3.0?4.5% of HL), the eye diameter
(3.6?5.8% of HL), the interocular distance (5.6?6.8% of
HL), the postocular length (36.7?40.3% of HL), the
height of the branchial opening (13.8?16.6% of HL),
the pectoral-fin length (38.5?45.7% of HL), and the tail
depth (12.7?17.5% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 6.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
distinctly curved ventrally. Mouth terminal and rela-
tively small, with rictus located anterior to vertical
through posterior naris. Anus and urogenital papilla
located ventral to head, situated along vertical
through eye. Combined opening for anus and urogeni-
tal papilla ovoid, with intraspecific proportional
variation in width of opening.
Premaxilla with eight to 11 teeth (N = 2) apparent
in whole specimen. Dentary with two tooth rows;
outer row with six teeth and inner row with four teeth
(N = 2).
Figure 36. Sternarchorhynchus curvirostris, illustration of syntype from Boulenger (1887).
Figure 37. Sternarchorhynchus curvirostris, female, 235 mm total length, MCZ 46676; Ecuador, Pastaza, R?o Putuno.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 293
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
T
a
b
le
6.
M
or
ph
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et
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r
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ea
n
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ta
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(m
m
)
20
3?
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7
(N
=
4)
?
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1
16
3?
17
2
(N
=
2)
?
16
8
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02
(N
=
9)
?
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(m
m
)
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8?
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=
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1
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6
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75
?1
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(N
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9)
?
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(m
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(N
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32
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(m
m
)
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(N
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4.
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(N
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?
14
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18
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(N
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8)
?
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se
83
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85
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88
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84
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9
(N
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85
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86
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79
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(N
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9)
82
.4
D
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s
9.
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12
.0
(N
=
4)
10
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11
.9
12
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?1
2.
7
(N
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12
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11
.4
11
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5.
4
(N
=
9)
13
.7
P
re
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n
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ce
11
.3
?1
3.
4
(N
=
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12
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15
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16
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6.
7
(N
=
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16
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14
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14
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8.
3
(N
=
9)
16
.3
P
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ct
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ce
18
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2.
5
(N
=
4)
20
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21
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22
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3.
2
(N
=
2)
22
.9
21
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19
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4.
6
(N
=
9)
22
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re
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dy
de
pt
h
12
.5
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0
(N
=
4)
13
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11
.9
11
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1.
2
(N
=
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11
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12
.6
11
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2.
7
(N
=
9)
11
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ea
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8
(N
=
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20
.0
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3.
0
(N
=
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22
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21
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20
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3.
7
(N
=
9)
22
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au
da
l
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n
gt
h
7.
9?
10
.4
(N
=
6)
9.
0
16
.9
15
.1
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6.
6
(N
=
2)
15
.8
9.
6
8.
7?
10
.8
(N
=
8)
9.
9
P
er
ce
n
t
of
h
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d
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gt
h
A
n
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s
to
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-fi
n
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n
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6.
8
(N
=
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3.
2
15
.0
13
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?1
7.
4
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=
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6.
8?
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(N
=
9)
9.
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P
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to
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l-
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.5
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5.
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(N
=
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35
.6
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7.
0
(N
=
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36
.3
31
.5
31
.5
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0.
7
(N
=
9)
34
.6
H
ea
d
de
pt
h
at
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e
27
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5.
4
(N
=
5)
30
.2
27
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25
.6
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7.
0
(N
=
2)
26
.3
30
.4
26
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0.
8
(N
=
9)
28
.6
H
ea
d
de
pt
h
at
n
ap
e
50
.9
?6
7.
3
(N
=
3)
57
.4
41
.4
39
.5
?4
2.
2
(N
=
2)
40
.9
43
.2
39
.5
?4
7.
6
(N
=
9)
43
.0
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ea
d
w
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th
18
.7
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0.
3
(N
=
5)
23
.1
20
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18
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9.
9
(N
=
2)
19
.4
20
.9
17
.9
?2
3.
3
(N
=
9)
21
.1
S
n
ou
t
le
n
gt
h
64
.5
?6
6.
1
(N
=
5)
65
.5
66
.0
63
.8
?6
4.
6
(N
=
2)
64
.2
63
.4
57
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6.
0
(N
=
9)
61
.8
P
os
te
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or
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to
sn
ou
t
6.
9?
7.
4
(N
=
2)
7.
2
6.
5
7.
2?
7.
5
(N
=
2)
7.
4
9.
6
7.
9?
10
.7
(N
=
9)
9.
4
P
os
te
ri
or
n
ar
is
to
ey
e
54
.5
?5
7.
1
(N
=
2)
55
.8
58
.0
53
.0
?5
4.
6
(N
=
2)
53
.8
52
.5
42
.5
?5
5.
5
(N
=
9)
50
.0
M
ou
th
le
n
gt
h
5.
1?
5.
7
(N
=
2)
5.
4
5.
0
4.
8?
5.
3
(N
=
2)
5.
0
6.
6
5.
8?
7.
6
(N
=
9)
6.
5
In
te
rn
ar
ia
l
di
st
an
ce
3.
0?
4.
5
(N
=
2)
3.
8
2.
0
2.
3?
3.
1
(N
=
2)
2.
7
2.
9
2.
2?
3.
5
(N
=
9)
2.
7
E
ye
di
am
et
er
3.
6?
5.
8
(N
=
5)
4.
6
4.
0
3.
8?
4.
3
(N
=
2)
4.
1
4.
6
3.
9?
6.
7
(N
=
9)
5.
0
In
te
ro
cu
la
r
w
id
th
5.
6?
6.
8
(N
=
5)
6.
2
5.
2
5.
4?
6.
2
(N
=
2)
5.
8
6.
3
5.
6?
13
.5
(N
=
9)
8.
3
P
os
to
cu
la
r
di
st
an
ce
36
.7
?4
0.
3
(N
=
5)
38
.2
38
.7
36
.1
?3
8.
6
(N
=
2)
37
.3
39
.8
35
.6
?3
9.
8
(N
=
9)
37
.9
B
ra
n
ch
ia
l
op
en
in
g
13
.8
?1
6.
6
(N
=
4)
15
.5
9.
5
10
.2
?1
0.
8
(N
=
2)
10
.5
11
.5
9.
8?
14
.0
(N
=
9)
11
.8
P
er
ce
n
t
of
ca
u
da
l
le
n
gt
h
T
ai
l
de
pt
h
12
.7
?1
7.
5
(N
=
4)
14
.7
8.
9
8.
0?
8.
6
(N
=
2)
8.
3
17
.1
13
.8
?1
9.
2
(N
=
8)
15
.8
C
au
da
l-
fi
n
le
n
gt
h
30
.3
?5
6.
9
(N
=
2)
43
.6
19
.7
17
.2
?2
1.
7
(N
=
2)
19
.1
29
.4
26
.6
?4
5.
0
(N
=
8)
34
.3
N
u
m
be
r
of
sp
ec
im
en
s
in
di
ca
te
d
in
pa
re
n
th
es
es
.
H
,
h
ol
ot
yp
e;
ra
n
ge
in
cl
u
de
s
n
on
ty
pe
sp
ec
im
en
s.
294 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Branchiostegal rays five; with first three rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16 (13 anterior; three
transitional; N = 1).
Pectoral-fin rays ii + 11?14 [ii + 11] (N = 5). Anal-fin
origin located anterior to opercle. Anterior
unbranched anal-fin rays 25 (N = 1). Total anal-fin
rays 173?180 [180] (N = 4). Scales above lateral line
at midbody nine to 11 [10] (N = 5). Scales present
along mid-dorsal line to origin of electroreceptive fila-
ment. Origin of midsaggital electroreceptive filament
located approximately at 59% of TL. Filament extend-
ing posteriorly to vertical through posterior terminus
of base of anal fin. Tail compressed and short, ending
in small, elongate, pointed caudal fin. Caudal-fin rays
15?16 (N = 3).
Coloration in alcohol: Available specimens including
syntypes variably depigmented. Overall coloration
tan to brown, but missing on some regions in some
nontype specimens as consequence of apparent post-
mortem damage. Head slightly lighter midventrally
and with narrow, lightly coloured mid-dorsal stripe
that commences midway along length of snout and
expands laterally in region above orbit into longitu-
dinally ovoid, more lightly pigmented area on dorsal
surface of postocular portion of head. Lightly coloured
region terminates posteriorly approximately at verti-
cal through anterior margin of opercle. Stripe obscure
in some individuals. Body tan to dark overall and
lacking distinct, narrow, lightly coloured mid-dorsal
stripe present in some congeners. Pectoral fin dusky
to dark. Anal fin nearly hyaline to dark, more so
basally. Caudal fin dusky to dark.
Distribution: Sternarchorhynchus curvirostris is
known from the R?o Bobanaza, eastern Ecuador and
perhaps from north-eastern Peru (Fig. 35; under
Remarks below).
Remarks: The original description of Sternarchus
(Rhamphosternarchus) curvirostris by Boulenger
(1887: 282) reported the length as 125 mm TL. The
two specimens now identified as the syntype series
(BMNH 1880.12.890-891) are, however, distinctly
longer than that length [note: Mago-Leccia (1994:
fig. 55) and Campos-da-Paz (2000: fig. 3) both labelled
a specimen as the ?type?, whereas there are two syn-
types]. Searches through the collections of the BMNH
failed to yield any other specimens of S. curvirostris
that correspond to the length reported in the species
description. It is impossible to determine whether the
reported original length was a lapsus or the pur-
ported types are not the material on which the species
was based. This question notwithstanding, the speci-
mens identified as the syntypes of Sternarchus
curvirostris (= Sternarchorhynchus curvirostris) oth-
erwise conform to the details in the original descrip-
tion of that species.
Eigenmann & Bean (1907: 666) proposed that S.
curvirostris might be a synonym of S. mormyrus on
the basis of specimens that originated in the lower
Amazon River between Manaus and Par? (= Bel?m).
They believed that those eastern Amazonian speci-
mens bridged the differences in morphometrics and
meristics purported to differentiate S. curvirostris
from S. mormyrus. Sternarchorhynchus curvirostris
along with S. mormyrus were, in turn, considered to
be junior synonyms of S. oxyrhynchus by Ellis (1913:
141), who recognized the latter species as a mono-
typic, morphologically highly variable form.
Fern?ndez-Y?pez (1967: 18) resurrected S. curviros-
tris (and S. mormyrus) from the synonymy of S.
oxyrhynchus on the basis of external features of the
head. The recognition of S. curvirostris as a distinct
species continued with Mago-Leccia (1994: 37),
Campos-da-Paz (2000: 528), and other authors. Based
on the information provided by Fern?ndez-Y?pez
(1967), the specimens that he considered to be S.
mormyrus were misidentified and it is highly ques-
tionable whether the specimen he identified as S.
curvirostris was that species. Notwithstanding the
fact that Fern?ndez-Y?pez based his conclusions on
erroneous information, our results confirm that S.
curvirostris is a distinct species. Various authors
followed Fern?ndez-Y?pez (1967) in considering
S. curvirostris a component of the Venezuelan ich-
thyofauna, but we have not examined any specimens
of the species that originated in that country or
regions proximate to it. It is likely that the original
citation represents a misidentification.
We located only five specimens of S. curvirostris in
museum collections, the two apparent syntypes
(BMNH 1880.12.8.90-91) and three other specimens
(MCZ 48676; USNM 163887) that were also collected
in the R?o Bobonaza, Ecuador, the river system from
which the type series originated. Three other speci-
mens from portions of north-eastern Peru proximate
to the type region (LACM 36324-2, LACM 36327-3)
would be considered conspecific with S. curvirostris
based on counts and overall form of the head and
body, but differ from Ecuadorian samples in the
degree of pigmentation on the snout. Although this
difference may be a consequence of differential pres-
ervation or geographical variation, we defer from for-
mally equating these specimens with S. curvirostris
at this time.
Secondary sexual dimorphism: Sternarchorhynchus
curvirostris is not known to demonstrate sexual
dimorphism.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 295
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Material examined
ECUADOR. Pastaza: Canelos (1?35?S, 77?45?W);
BMNH 1880.12.8.90-91, 2 (length undetermined
because of missing tail-203.2; syntypes of Sternarcho-
rhynchus (Rhamphosternarchus) curvirostris; See
remarks concerning the reported type status of these
specimens). R?o Putuno, tributary of R?o Bobonaza;
MCZ 48676, 1 (235). Upper R?o Pastaza basin, R?o
Bobonaza, Chicirota (2?22?S, 76?38?W), USNM
163887, 2 (217?240).
The following specimens may be S. curvirostris (see
Remarks above).
PERU. Amazonas: R?o Santiago at La Poza (4?01?S,
75?18W); LACM 36324-2, 1 (189), LACM 36327-3, 2
(150?238).
STERNARCHORHYNCHUS FREEMANI SP. NOV.
(FIGS 35, 38; TABLE 6)
Sternarchorhynchus oxyrhynchus, not of M?ller &
Troschel, Eigenmann, 1912: 438 [in part, specimens
from Guyana, Warraputa, and Amatuk]. ? Ellis, 1913:
141, 174 [in part, specimens from Guyana, Warra-
puta, and Amatuk; diet].
Diagnosis: Sternarchorhynchus freemani is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the absence of scales along the mid-dorsal
region of the body as far posteriorly as the vertical
through posterior limit of the pectoral fin, the pres-
ence of a more lightly coloured narrow band of mid-
dorsal pigmentation on the head and mid-dorsal
region of the body extending as far posteriorly as the
origin of the electroreceptive filament and sometimes
beyond that point, the presence of four to five pre-
maxillary teeth, 16?17 precaudal vertebrae, 26?28
anterior unbranched anal-fin rays, 170?177 total
anal-fin rays, eight to nine scales above the lateral
line at the midbody, the termination of the electrore-
ceptive filament at the vertical running through a
point four scales posterior of the posterior limit of the
base of the anal fin, the termination of the lateral line
at a point four scales anterior of the base of the
caudal fin, the greatest body depth (11.0?11.9% of
LEA), the distance from the anus to the anal-fin
insertion (13.0?17.4% of HL), the caudal length (15.1?
16.9% of LEA), the head width (18.8?20.4% of HL),
the distance from the posterior naris to the snout
(6.5?7.5% of HL), the interocular width (5.2?6.2% of
HL), the postocular distance (36.1?38.7% of HL), the
height of the branchial opening (9.5?10.8% of HL),
the head depth at the eye (25.6?27.7% of HL), and the
tail depth (8.0?8.9% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 6.
Lateral line extending posteriorly to point four
scales from base of caudal fin and absent on remain-
der of tail and on caudal fin. Snout elongate, com-
pressed and slightly curved ventrally along its
anterior portion. Mouth terminal. Rictus located
slightly anterior to vertical through anterior naris.
Anus and urogenital papilla located ventral to head,
either situated approximately at vertical through eye
or along vertical one eye diameter anterior to margin
of eye. Combined opening for anus and urogenital
papilla longitudinally ovoid in all specimens.
Figure 38. Sternarchorhynchus freemani sp. nov., holotype, male, 201 mm total length, CAS 72246; Guyana,
Amatuk, Lower Potaro River.
296 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Premaxilla with four to five teeth (N = 2) apparent
in whole specimens. Dentary with two tooth rows;
outer row with eight teeth and inner row with one to
two teeth (N = 2).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16?17 (12?14 ante-
rior; two to four transitional; N = 4).
Pectoral-fin rays ii + 11?12 [ii + 11] (N = 4). Anal-fin
origin located anterior to opercle. Anterior
unbranched anal-fin rays 22?28 [22] (N = 4). Total
anal-fin rays 170?177 [176] (N = 4). Scales above
lateral line at midbody eight to nine [8] (N = 4). Scales
absent along mid-dorsal region of body from rear of
head posteriorly to point approximately along vertical
through posterior limit of pectoral fin. Scaleless
region followed by area with sparse mid-dorsal scales
and then fully scaled region extending to origin of
midsaggital electroreceptive filament. Origin of mid-
saggital electroreceptive filament located on posterior
half of body, approximately 60% of TL. Filament
extending posteriorly four scales beyond vertical
through posterior terminus of base of anal fin. Tail
compressed and moderate, ending in small,
elongate, pointed caudal fin. Caudal-fin rays 13?16
[13] (N = 4).
Coloration in alcohol: Overall coloration of head and
body ranging from tan to brown. More lightly pig-
mented specimen with narrow band of darker pig-
mentation extending anteriorly from eye nearly to tip
of snout and with second darker band extending along
ventral portions of snout. Two bands of darker pig-
mentation border more lightly pigmented region
extending along lateral surface of snout. Dark bands
and intervening more lightly coloured area on snout
less apparent in overall darkly pigmented individu-
als. Dorsal dark band forms lateral margin of narrow,
lightly coloured stripe running along mid-dorsal
region of snout; mid-dorsal stripe terminates above
eye, or slightly posterior of that point. Mid-dorsal
stripe on anterior portion of head separated from
mid-dorsal stripe on body by dark pigmentation on
dorsal surface of head in postocular region. Body with
mid-dorsal more lightly pigmented stripe extending
from rear of head to origin of electroreceptive filament
or to varying degrees posterior of that point. Pectoral
fin in overall more lightly coloured specimens hyaline
but somewhat dusky with small dark chromatophores
overlying fin rays in darker individuals. Anal fin
ranging from hyaline to dusky, with darker individu-
als having small, dark chromatophores overlying fin
rays. Caudal fin dark, more so in overall darker
individuals, with distal regions somewhat more
lightly coloured.
Distribution: Sternarchorhynchus freemani is only
known from locations in the lower portions of the
Essequibo River basin in Guyana (Fig. 35).
Ecology: Ellis (1913: 174) reported that S. freemani
(specimens identified as S. oxyrhynchus by that
author) feeds on various types of aquatic larvae and
annelids.
Secondary sexual dimorphism: No sexual dimorphism
was apparent in the limited available sample of S.
freemani.
Etymology: The species name, freemani, is in honour
of Bryon J. Freeman of the University of Georgia who
provided the senior author with invaluable assistance
at the Georgia Museum of Natural History.
Remarks: Eigenmann (1912: 438) and Ellis, 1913:
141) reported S. oxyrhynchus from Amatuk and War-
raputa in the Essequibo River system of Guyana.
More recently Watkins et al. (2004) cited that species
from streams of the Iwokrama forest along the left
bank of the Essequibo. As discussed under Remarks
for S. oxyrhynchus, none of the examined samples of
Sternarchorhynchus from Guyana proved to be S.
oxyrhynchus. Examination of the material that served
at least in part as the basis of the Eigenmann and
Ellis citations of S. oxyrhynchus (CAS 72248 formerly
CM 1807; CAS 72246, formerly IU 12590) have shown
that they are S. freemani, a new species described in
this study.
M?ller & Troschel (1848) reported that the material
on which they based their description of S. oxyrhyn-
chus originated in the Essequibo River, Guyana. As
mentioned within the Remarks section under S. oxy-
rhynchus, none of the samples of that species we
examined originated in the Essequibo River or any
other river in the Guianas. Rather, all examined
specimens of S. oxyrhynchus were captured in the R?o
Orinoco basin. Samples of Sternarchorhynchus that
originated in the Essequibo River are all S. freemani,
a species distinguished from S. oxyrhynchus by
numerous features. One other species of Sternarcho-
rhynchus was discovered in samples from the easterly
flowing rivers of the Guianas; that being S. galibi, a
species apparently endemic to the Marowijne River
(= Fleuve Maroni) system along the border between
Suriname and French Guiana. Sternarchorhynchus
galibi and S. oxyrhynchus differ in diverse features,
most notably in mouth form.
Material examined
Holotype: ? GUYANA. Essequibo River basin, Lower
Potaro River at Amatuk (approximately 5?18?N,
59?18W), collected by C. H. Eigenmann, 10.x.1908;
CAS 72246, (201, male).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 297
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Paratypes: ? GUYANA. Essequibo River basin, Lower
Potaro River at Amatuk (approximately 5?18?N,
59?18W), collected by C. H. Eigenmann with the
holotype, CAS 227622 ex CAS 72246, 1 (163, female;
originally two specimens, but one female was lost
during the clearing and staining process but photo-
graphed and radiographed), Essequibo River basin,
lower Potaro River at Warraputa cataract; CAS
72248, 1 (185).
STERNARCHORHYNCHUS GALIBI SP. NOV.
(FIGS 35, 39; TABLE 6)
Diagnosis: Sternarchorhynchus galibi is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the absence of scales along the mid-dorsal
region of the body as far posteriorly as the vertical
through the posterior limit of the pectoral fin, the
presence of a more lightly coloured narrow band of
mid-dorsal pigmentation on the head and mid-dorsal
region of the body extending as far posteriorly as the
origin of the electroreceptive filament and sometimes
beyond that point, the presence of six to ten premax-
illary teeth, 26?31 anterior unbranched anal-fin rays,
169?179 total anal-fin rays, and seven to ten scales
above the lateral line at the midbody, the termination
of the electroreceptive filament at the vertical
running through a point one or two scales anterior of
the posterior limit of the base of the anal fin, the
termination of the lateral line at a point three or four
scales anterior of the base of the caudal fin, the
greatest body depth (11.1?12.7% of LEA), the caudal
length (8.7?10.8% of LEA), the distance from the anus
to the anal-fin insertion (6.8?12.8% of HL), the head
width (17.9?23.3% of HL), eye diameter (3.9?6.7 of
HL), the head depth at the eye (26.2?30.8% of HL),
the head depth at the nape (39.5?47.6% of HL), the
postocular distance (35.6?39.8% of HL), the pectoral-
fin length (31.5?40.7% of HL), and the tail depth
(13.8?19.2% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 6.
Lateral line extending posteriorly to point three or
four scales anterior of base of caudal fin but absent on
remainder of tail and on caudal fin. Snout elongate,
compressed and slightly curved ventrally along ante-
rior portion. Mouth terminal. Rictus located along
vertical through anterior naris. Anus and urogenital
papilla located ventral to head, with position in
smaller specimens located within area delimited ante-
riorly by vertical running approximately to eye and
posteriorly one orbital diameter posterior of eye.
Openings positioned one eye diameter anterior to
vertical through eye in larger individuals. Combined
opening for anus and urogenital papilla circular in
smaller individuals and longitudinally ovoid in larger
specimens.
Premaxilla with six to ten teeth (N = 4) apparent in
whole specimens. Dentary with two tooth rows; outer
row with six to nine teeth and inner row with one to
three teeth (N = 4).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15?16 (11?12 ante-
rior; four transitional; N = 2).
Pectoral-fin rays ii + 12?13 [ii + 12] (N = 10). Anal-
fin origin located anterior to opercle. Anterior
unbranched anal-fin rays 26?31 [26] (N = 8). Total
anal-fin rays 169?179 [175] (N = 10). Scales above
lateral line at midbody seven to ten [10] (N = 10).
Scales absent along mid-dorsal region of body from
rear of head posteriorly to point approximately one-
third of distance along length of body and three times
length of pectoral fin from rear of head. Scaleless
region followed by fully scaled mid-dorsal area to
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located on
posterior half of body, approximately 70% of TL. Fila-
ment extending to point one or two scales short of
vertical through posterior terminus of base of anal fin
to vertical through latter landmark. Tail compressed
and short, ending in small, elongate, pointed caudal
fin. Caudal-fin rays 15?17 [15] (N = 9).
Coloration in alcohol: Overall coloration of head and
body dark brown. Slightly darker bands of pigmen-
tation extending anteriorly from eye along dorsolat-
Figure 39. Sternarchorhynchus galibi sp. nov., holotype, female, 168 mm total length, ZMA 109.366; Suriname,
Marowijne District, Lawa River at Stroomafwaarts Rapids near Anapaikekondre.
298 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
eral portion of snout and along ventral portions of
snout. Dark bands border more lightly pigmented
region on midlateral surface of anterior half of
snout. Dorsal dark band forms lateral margin of
narrow, lightly coloured stripe running along mid-
dorsal region of snout; stripe terminates above eye,
or slightly posterior of that point. Mid-dorsal stripe
on snout separated from mid-dorsal stripe on body
by dark pigmentation on dorsal surface of head in
postocular region. Body with more lightly pig-
mented, mid-dorsal stripe extending from rear of
head to origin of electroreceptive filament or to
varying degrees posterior of that point. Pectoral fin
dusky with small, dark chromatophores overlying
fin rays. Anal fin dusky with small, dark chromato-
phores overlying fin rays. Caudal fin dark with
distal regions hyaline.
Distribution: Sternarchorhynchus galibi is known
from the Lawa River, Marowijne River (= Fleuve
Maroni) basin along the border between Suriname
and French Guiana (Fig. 35).
Secondary sexual dimorphism: No sexual dimorphism
was apparent in the limited available sample of
S. galibi.
Etymology: The species name, galibi, is in reference to
the town of that name begun as a major settlement of
the indigenous Caribs. The town is at the mouth of
the Marowijne, the drainage system that includes the
type locality of S. galibi.
Remarks: Sternarchorhynchus oxyrhynchus was cited
by Meunier (2004: 89) as occurring in the upper
portions of the Fleuve Maroni (= Marowijne River in
French Guiana); however, it is likely that this citation
was based on S. galibi.
Material examined
Holotype: ? SURINAME. Marowijne District: Lawa
River at Stroomafwaarts Rapids near Anapaikekon-
dre (= Anapaike country; Anapaike at 3?34?N,
54?39?W), collected by J. P. Gosse, 18.xi.1966, ZMA
109.366 (168, originally part of IRSCNB 16793,
apparently female).
Paratypes: ? SURINAME. Marowijne District: Lawa
River at Stroomafwaarts Rapids near Anapaikekon-
dre (= Anapaike country; Anapaike at 3?34?N,
54?39?W), ZMA 124.524, 1 (121), IRSCNB 16793, 7
(80?202); collected with the holotype by J. P. Gosse,
18.xi.1966. Lawa River base camp, approximately
8 km south-south-west of Anapaike/Kawahaken (air-
strip) (3?19?31?N, 54?03?48?W), collected by J. Lund-
berg, M. Sabaj, P. Willink, and J. Mol, 18.iv.2007,
ANSP 187155, 1 (200).
Nontype specimen: ? FRENCH GUIANA. Upper
Maroni River (no specific locality), MHNG 2167.45, 1
(143).
STERNARCHORHYNCHUS GNOMUS DE SANTANA &
TAPHORN (FIGS 35, 40; TABLE 7)
Sternarchorhynchus gnomus de Santana & Taphorn,
2006: 2, figs 1, 2 [type locality: Venezuela, Bolivar, R?o
Caroni, at confluence with R?o Claro, 7?54?30?N,
63?02?50?W].
Diagnosis: Sternarchorhynchus gnomus is distin-
guished from congeners by the following combination
Figure 40. Sternarchorhynchus gnomus, holotype, female, 133.5 mm total length, MCNG 53963; Venezuela, Bolivar, R?o
Caron?.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 299
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
T
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.
300 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the presence of a definite series of scales along
the mid-dorsal region of the body, the lateral line that
extends to the base of the caudal fin, the absence of a
more lightly coloured narrow band of mid-dorsal pig-
mentation on the head and mid-dorsal region of the
body anterior of the origin of the electroreceptive
filament or with the stripe very obscure, the hyaline
anal fin lacking a dark band along its distal margin,
the possession of six to eight premaxillary teeth, one
row of dentary dentition with seven to eight teeth, 12
branched pectoral-fin rays, 15 precaudal vertebrae,
21?25 anterior unbranched anal-fin rays, 156?177
total anal-fin rays, six to seven scales above the
lateral line at the midbody, ten to 12 caudal fin-rays,
the greatest body depth (9.3?11.4% of LEA), the dis-
tance from the snout to the anus (11.8?17.4% of LEA),
the preanal distance (14.1?17.7% of LEA), the
prepectoral-fin distance (20.0?23.2% of LEA), the
caudal length (10.1?17.4% of LEA), the head length
(20.1?24.3% of LEA), the snout length (57.6?65.4% of
HL), the head depth at the nape (39.7?44.9% of HL),
the postocular distance (36.9?41.6% of HL), the
pectoral-fin length (34.8?41.0% of HL), and the tail
depth (8.3?13.8% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 7.
Lateral line extending posteriorly to approximately
three to four scales anterior of base of caudal fin, but
absent fin. Snout elongate, compressed and slightly
curved ventrally along anterior portion. Mouth termi-
nal. Rictus located distinctly anterior of vertical
through anterior naris. Anus and urogenital papilla
located ventral to head. Openings located at vertical
approximately two eyes diameter posterior of margin
of orbit in largest specimens. Combined opening for
anus and urogenital papilla longitudinally ovoid.
Premaxilla with six teeth (N = 1) in cleared and
stained specimen, seven to eight apparent in whole
specimens (N = 4). Dentary with one tooth row with
seven functional and five replacement teeth in cleared
and stained specimen (N = 1), six to eight functional
plus three replacement teeth apparent in whole speci-
mens (N = 4).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15 (13 anterior; two
transitional; N = 4).
Pectoral-fin rays ii + 12 [ii + 12] (N = 10). Anal-fin
origin located anterior to opercle. Anterior
unbranched anal-fin rays 21?25 (N = 5). Total anal-fin
rays 159?177 [175] (N = 9). Scales above lateral line
at midbody six to seven [7] (N = 10). Scales present
along mid-dorsal region of body to origin of midsag-
gital electroreceptive filament. Origin of midsaggital
electroreceptive filament located on posterior half of
body, approximately 60% of TL. Filament extending
posteriorly to vertical through posterior terminus of
base of anal fin. Tail compressed and moderate,
ending in small, elongate, pointed caudal fin. Caudal-
fin rays ten to 12 (N = 4).
Coloration in alcohol: Overall coloration of head and
body dark brown. Slightly darker bands of pigmenta-
tion extending from anterior of orbit anteriorly along
dorsolateral portion of snout and along ventral por-
tions of snout. Two dark bands border more lightly
pigmented region on midlateral surface of anterior
half of snout. Mid-dorsal region of head and body with
narrow, more lightly coloured, irregularly interrupted
stripe extending to origin of midsaggital electrorecep-
tive filament. Pectoral and anal fins hyaline. Caudal
fin dark with distal regions hyaline.
Distribution: Sternarchorhynchus gnomus is known
from the lower portions of the R?o Caroni basin,
Venezuela (Fig. 35). The type locality is now sub-
merged by the waters of the Caruachi Reservoir (de
Santana & Taphorn, 2006: 1).
Ecology: The type locality of S. gnomus was a side
channel of the R?o Caroni near its confluence with the
R?o Claro. At that site, the water was clear with a
visibility of approximately 2 m and the pH ranging
from 6.6?7.6. Stomach contents of the species
included chironomids, ephemeropterans, and
trichopterans.
Secondary sexual dimorphism: Sexually mature males
of S. gnomus appear to have the ventral curvature of
the snout more pronounced than do females of compa-
rable sizes (de Santana & Taphorn, 2006: fig. 2).
Material examined
VENEZUELA. Bolivar: R?o Caron?, at its confluence
with R?o Claro (7?54?30?N 63?02?50?W); ANSP
182798, 1 (108.8; paratype); INPA 182798, 3 (one
cleared and stained, 145.0?152.0; paratypes); MCNG
53963, 1 (133.5; holotype, female); MCNG 18435,
5 (76.5?152.0; paratypes).
STERNARCHORHYNCHUS GOELDII SP. NOV.
(FIGS 41, 42; TABLE 7)
Diagnosis: Sternarchorhynchus goeldii is distin-
guished from all congeners with the exception of S.
oxyrhynchus by having the gape of the mouth aligned
with main axis of snout, with the gape elongate and
extending posteriorly distinctly beyond the vertical
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 301
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
through posterior naris contrary to a shorter gape
that terminates posteriorly at, or slightly short of, the
vertical through anterior nares. Sternarchorhynchus
goeldii differs from S. oxyrhynchus in the number of
total vertebrae (92?94 versus 97?108, respectively),
the greatest body depth (8.2?10.8 versus 6.3?8.2% of
TL, respectively), and to a large degree in the head
depth at the nape (35.0?44.8 versus 26.8?37.7% of SL,
respectively).
Description: Morphometric data for holotype and
paratypes specimens in Table 7.
Lateral line extending posteriorly to base of caudal
fin, but not extending onto fin. Snout elongate, com-
pressed and very slightly curved ventrally along its
distal portion, but having overall anteroventral ori-
entation. Anus and urogenital papilla located ventral
to head, with position ranging from slightly anterior
of vertical through anterior margin of orbit to vertical
Figure 41. Sternarchorhynchus goeldii sp. nov., holotype, female, 306 mm total length, INPA 28378; Brazil, Ama-
zonas, Rio Purus.
Figure 42. Map of central and northern South America showing geographical distribution of Sternarchorhynchus
goeldii sp. nov. (1 = holotype locality; species also collected in region of type locality of Sternarchorhynchus higuchii
sp. nov., star), Sternarchorhynchus hagedornae sp. nov. (2 = holotype locality), S. higuchii sp. nov. (3 = holotype
locality), and Sternarchorhynchus inpai sp. nov. (4 = holotype locality) (some symbols represent more than one locality
and/or lot of specimens).
302 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
located two orbital diameters posterior of vertical
through rear of orbit. Anus and urogenital papilla
generally more anteriorly positioned in larger speci-
mens. Combined opening for anus and urogenital
papilla longitudinally ovoid.
Premaxilla with ten to 11 teeth with six replace-
ment teeth in cleared and stained specimen (N = 6).
No sexual dimorphism in form of dentary or dentary
dentition apparent in examined samples. Dentary
with two rows of teeth. Outer row consisting of 13?20
curved conical teeth and inner row with three to five
teeth (N = 7). Mouth terminal. Gape of mouth aligned
with main axis of snout, elongate and extending pos-
teriorly distinctly beyond vertical through posterior
naris (Fig. 1A). Lower jaw with terminal fleshy pad
that extends anteriorly beyond vertical through ante-
rior limit of snout. Fleshy pad directed dorsally and
overlaps tip of snout when mouth closed.
Branchiostegal rays five; with first and second ray
narrow and elongate, third to fifth rays becoming
progressively wider. Precaudal vertebrae 16?17 (three
anterior; three to four transitional; N = 15). Total ver-
tebrae 92?94 (N = 10).
Pectoral-fin rays ii + 12?14 [ii + 13] (N = 29). Anal-
fin origin located anterior to vertical through opercle.
Anterior unbranched anal-fin rays 21?40 [26]
(N = 17). Total anal-fin rays 204?237 [215] (N = 29).
Scales above lateral line at midbody three to six [5]
(N = 21). Scales absent along mid-dorsal line from
rear of head to origin of electroreceptive filament.
Origin of midsaggital electroreceptive filament
located approximately at 62% of TL. Filament extend-
ing posteriorly beyond vertical through posterior ter-
minus of base of anal fin for distance of approximately
five scales. Tail compressed and short, ending in
small, elongate caudal fin with rounded posterior
margin. Caudal-fin rays 16?22 [20] (N = 13).
Coloration in alcohol: Overall ground coloration tan
to dark brown. Head and body with small dark chro-
matophores relatively densely scattered over sur-
faces. Chromatophores more densely packed and
more intensely pigmented in darker specimens.
Portion of head anterior of orbit somewhat darker
than remaining region of head in some specimens.
Some specimens with posteriormost portion of body
and all of tail distinctly darker than remainder of
body.
Pectoral fin ranging from nearly completely hyaline
to overall darkly pigmented, but with dark pigmen-
tation most developed on distal portions and along
dorsal margin of fin. Very lightly pigmented speci-
mens with dark pigmentation limited to distalmost
portions and dorsal margin of fin. Overall darkly
pigmented specimens with dark pigmentation cover-
ing distal half to two-thirds of pectoral fin. Distal
portions of anal fin variably dark. Overall more
lightly pigmented specimens often with distal dark
pigmentation barely apparent on anteriormost
portion of anal fin and with obvious dark coloration
present only as narrow band along distal portion of
fin. Some other individuals with distal dark pigmen-
tation extending forward to anterior limit of fin and
with broad irregular band of dark pigmentation
extending along most of distal portion of fin. Caudal
fin dark even in overall lightly pigmented individuals
and very dark in most specimens.
Distribution: Sternarchorhynchus goeldii is distrib-
uted along the main stream of the Amazon from the
region of ?bidos, Brazil, in the eastern portions of the
Amazon basin westwards to north-eastern Peru. The
species also occurs to varying degrees in the lower
courses of tributary rivers of the main Amazon
(Fig. 42).
Electrical organ discharge: Crampton (1998) and
Crampton & Albert (2006) reported that individuals
of S. goeldii (identified therein as Sternarchorhynchus
oxyrhynchus) have a type D EOD pattern with a
fundamental frequency of 1321?1390 Hz.
Habits: Crampton (2007: 330) reported on the activity
pattern of S. goeldii (identified by that author as S.
oxyrhynchus) in an aquarium setting under subdued
natural light. In that setting the species demon-
strated increased activity levels at night, but only
sporadic foraging activities in the course of the day.
Secondary sexual dimorphism: No secondary sexual
dimorphism comparable to that found in many
congeners was apparent in exampled samples of
S. goeldii.
Etymology: The species name, goeldii, is in honour of
Emilio Goeldi, who made many contributions to our
knowledge of many groups of Amazonian animals
including fishes.
Material examined
Holotype: ? BRAZIL. Amazonas: Rio Purus
(3?50?06?S, 61?23?59?W); collected by M. Toledo-Piza
et al., 26.vii.1996; INPA 28378 (306, formerly USNM
375467).
Paratypes: ? BRAZIL. Amazonas: Rio Solim?es, down-
stream from mouth of R?o Purus, upstream from town
of Manacapuru (3?27?22?S, 60?45?21?W) FMNH
115520, 1 (193). Rio Purus (4?53?47?S, 62?54?53?W);
INPA 17104, 2 (175?202). Rio Amazonas, 20.6 km
above Itacoatiara, 35.5 km below Santa Antonia
(3?15?46?S, 58?36?02?W), collected by F. Langeani
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 303
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
et al., 20.x.1994; USNM 373081, 1 (212). Rio
Solim?es, Costa do Marimba, Ilha do Careiro, col-
lected by C. Cox-Fernandes et al.; INPA 17633, 4
(285?336). Rio Solim?es, near ?encontro das ?guas?
(area of mixing of waters of Rio Negro and Rio Ama-
zonas, collected by C. Cox-Fernandes et al.; INPA
24109, 5 (335?367).
Nontype specimens: ? BRAZIL. Amazonas: Rio Negro,
between tributary Rios Cuieras and Taruma-A?u,
between towns of Santa Maria and Lepros?rio
(3?01?45?S, 60?24?7?W); FMNH 115505, 4 (213?263),
FMNH 115506, 4 (162?244). Rio Ja?, curve of Ja?,
Novo Air?o; INPA 11355, 1 (184). Rio Ja?, mouth of
R?o Preto, Novo Air?o; INPA 12548, 1 (133), INPA
12551, 2 (176?217), INPA 12656, 1 (194). Rio Negro,
12 km above Lepros?rio, 16.3 km below Santa Maria
(3?02?58?S, 60?22?10?W); USNM 373069, 3 (221?257).
Rio Negro 4 km above Manaus (3?08?S, 60?03?W);
USNM 373044, 2 (231?251). Rio Negro, between
Paran? da Floresta and Paran? da Cotia, between
towns of Moura and S?o Francisco (1?33?48?S,
61?33?3?W); FMNH 115507, 1 (231). Rio Negro,
18.5 km above S?o Francisco (1?33?45?S, 61?33?01?W);
USNM 373075, 1 (221). Rio Negro, USNM 373046, 2
(225?243). Rio Negro, above Manaus; MCZ 98360, 1
(210). Rio Negro, between tributary drainages
Curidique and Paran? Jacar?, between towns of Novo
Caioe and S?o Francisco de Assis (1?58?30?S,
61?14?20?W); FMNH 115508, 4 (180?256). Rio Negro,
upstream from tributary drainage Tarum?-Mirim and
upstream from city of Manaus (3?04?11?S,
60?11?03?W); FMNH 115517, 1 (272). Rio Negro,
upstream from Manaus (3?1?18?S, 60?23?29?W);
FMNH 115516, 1 (326). Rio Negro, Praia Grande,
Manaus; INPA 27495 1 (235). Rio Solim?es, Manaus;
INPA 24111, 2 (335?339). Rio Negro, near Manaus;
INPA 4435, 3 (180?303). Rio Negro, 5.6 km below S?o
Francisco de Assis (1?42?42?S 61?24?27?W); USNM
373106, 3 (173?207). Rio Negro, 33 km below Novo
Caioe, 7 km above S?o Francisco de Assis (1?58?24?S,
61?14?30?W); USNM 373886, 1 (214). Rio Ja?, mouth
of Ja?; INPA 12551, 2 (176?217). Rio Ja?, mouth of
Rio Preto; INPA 11355, 1 (184), INPA 12656, 1 (191).
Rio Amazonas, Paran? do Tapar?; INPA 19991, 1
(203). Rio Solim?es, Paran? do Xiborena, INPA 17636,
1 (354). Rio Solim?es, Paran? do Xiborena; INPA
24110 1 (285). Rio Solim?es, Ilha do Careiro, Paran?
do Rei; INPA 27497, 1 (353). Rio Solimoes, Lago
Januac?, Manaquiri, INPA 27499, 5 (345?360). Rio
Solim?es, Paran? do Tapar?, Autazes; INPA 19991, 1
(200). Rio Purus, Beab? (4?53?47?S, 62?54?51?W);
INPA 17104, 2 (173?211). Rio Solim?es, Ilha do
Careiro, Paran? do Rei; INPA 17634 1 (288), INPA
17637, 1 (347), INPA uncat., 1 (353), INPA uncat., 1
(370). Rio Japur? between mouth of Lagos Mamirau?
and Joaquim; INPA 18274, 1 (334). Rio Japur?, at
mouth of Lago Mamirau?; INPA uncat., 1 (214). Rio
Tef? at Tef?; INPA 15821, 6 (315?370). Rio Tef?, Toco
Preto; INPA 15821, 6 (311?369). Rio Amazonas,
upstream from mouth of Rio Madeira/Paran? da Eva,
upstream from town of Novo Oriente (3?13?37?S,
59?3?32?W); FMNH 115519, 7 (193?295). Rio
Solim?es, below mouth of Rio Madeira; INPA 20221,
28 (230?313). Rio Solim?es, Paran? Xiborena; INPA
16636, 1 (357). Rio Amazonas downstream from Rio
Madeira, upstream from town of Itacoatiara
(3?20?9?S, 58?36?11?W); FMNH 115518, 1 (289). Rio
Uatum?, Presidente Figueiredo at Balbina Dam;
INPA 4833, 1 (341). Rio Juru?, tributaries Lago Paua-
pixuna and Rio Solim?es, between towns of Paua-
pixuna and Vit?ria (2?41?11?S, 65?48?30?W); FMNH
115503, 2 (257?282). Rio Juru? between Lago Paua-
pixuna and Rio Solim?es, between towns of Paua-
pixuna and Vit?ria (2?41?11?S, 65?48?30?W); FMNH
115503, 2 (257?282). Rio Juru?, Lago Pauapixuna
and Lago Meneroa, between towns of Pauapixuna and
Tamanicoa (2?46?31?S, 65?50?00?W); FMNH 115509, 1
(283). Rio Juru?, between Lago Pauapixuna and Rio
Solim?es, between towns of Pauapixuna and Vit?ria
(2?41?08?S, 65?48?29?W); FMNH 115502, 1 (289). Rio
Juta?, between mouths of Rio Zinho and Rio Solim?es,
between towns of Porto Antunes and Copatana
(2?51?16?S, 66?57?23?W); FMNH 115510, 1 (257). Rio
Juru? tributaries Lago Pauapixuna and Meneroa,
between towns of Pauapixuna and Tamanicoa
(2?46?31?S, 65?50?00?W); FMNH 115509, 1 (283). Rio
Juru?, between Lago Pauapixuna and Rio Solim?es,
between towns of Pauapixuna and Vit?ria (2?41?08?S,
65?48?29?W); FMNH 115502, 1 (289). Rio Solim?es,
downstream from mouth of Rio Purus, upstream from
Manacapuru (3?27?22?S, 60?45?21?W); FMNH 115520,
1 (193). Rio Solim?es, Lago Manacapuru; MCZ 9340,
2 (200?355), MCZ 24934, 1 (350). Rio Juta?, between
Rio Zinho and Rio Solim?es, between towns of Porto
Antunes and Copatana (2?51?16?S, 66?57?23?W);
FMNH 115510, 1 (257). Rio Juta?, between Porto
Antunes and Foz do Juta? (2?53?00?S, 66?58?22?W);
USNM 375482, 2 (351?353). Rio Solim?es (3?36?19?S,
61?18?39?W); USNM 375398, 2 (210?216). Rio
Solim?es (3?35?43?S, 61?07?16?W); USNM 375399, 1
(261). Par?: Rio Tocantins, Tucuru?; INPA 1501, 1
(220). Rio Amazonas between tributaries Paran? de
Jurut? and Trombetas, between towns of Jurut? and
?bidos (2?00?39?S, 55?55?17?W); FMNH 115511, 1
(259). Rio Trombetas between tributaries Furo Maria
Tereza and Amazonas, between towns of Fazenda
Santana and ?bidos (1?52?53?S, 55?38?13?W); FMNH
115512, 1 (183). Rio Trombetas, between tributaries
Lago Bacabal and Lago Samauma (1?31?3?S,
56?9?57?W); FMNH 115513, 2 (not measured). Rio
Trombetas, between Rio Cumina and Lago Axipica,
304 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
between towns of Bom Jesus and Santa Cecilia
(1?32?40?S; 56?01?07?W); FMNH 115514, 1 (245). Rio
Amazonas, 58.5 km below Jurut?, 21.1 km above
?bidos (1?55?48?S, 55?40?41?W); USNM 373040, 4
(329?368). Roraima: Rio Negro, at confluence with
Rio Branco or along lower 30 mi (48 km) below Rio
Branco (approximately 1?24?S, 61?27?W); MCZ 46887,
3 (1 CS, 190?215).
PERU. Loreto: Rio Amazonas, beach along east
bank of east channel of river, opposite Iquitos; INHS
55418, 3 (224?283).
STERNARCHORHYNCHUS HAGEDORNAE SP. NOV.
(FIGS 42?44; TABLE 7)
Sternarchorhynchus sp., Ortega, 1996: 469 [Peru,
Manu Biosphere Reserve, Rio Manu and Quebrada de
Pachija, tributary to Rio Manu]. ? Hagedorn & Keller,
1996: 493, fig. 2f [Peru, Manu Biosphere Reserve,
Quebrada de Pachija, tributary to Rio Manu; habitat,
EOD, secondary sexual dimorphism].
Diagnosis: Sternarchorhynchus hagedornae is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through anterior
nares, the distinctly longitudinally elongate combined
opening for the anus and the urogenital opening, the
sparse scales covered by skin along the mid-dorsal
portion of the body anterior to the origin of the
electroreceptive filament, the consistently dark
overall coloration of the head and body, the presence
of a more lightly coloured, narrow band of mid-dorsal
pigmentation on the head and mid-dorsal region of
the body anterior of the origin of the electroreceptive
filament and sometimes posterior of that point, the
absence of a very dark band of pigmentation at the
base of the enlarged patch of dentition on the dentary
in mature males, the possession of five to six teeth in
the outer tooth row of the dentary, 27?35 anterior
unbranched anal-fin rays, 173?193 total anal-fin rays,
nine to 13 scales above the lateral line at the midbody,
the greatest body depth (11.4?13.3% of LEA), the
length of the anal-fin base (86.6?89.6% of LEA),
the prepectoral-fin distance (17.6?20.8% of LEA), the
caudal length (5.5?8.3% of LEA), the head depth at
the nape (53.1?59.2% of HL), the head width (24.1?
28.3% of HL), the distance from the posterior naris to
the snout (8.7?9.8% of HL), the mouth length (6.4?
8.6% of HL), the interocular width (6.0?8.5% of HL),
the distance from the posterior naris to the eye (44.6?
48.9% of HL), the postocular distance (43.6?46.2% of
HL), the pectoral-fin length (39.1?46.9% of HL), and
the tail depth (21.3?30.4% of caudal length).
Description: Morphometric data for holotype and
paratypes in Table 7.
Lateral line extending to base of caudal fin, but
absent on fin. Snout elongate, compressed and
straight. Posterior naris closer to tip of snout than to
anterior margin of orbit. Branchial opening restricted
and situated slightly anterior to vertical through
pectoral-fin origin. Location of anus and urogenital
papilla apparently ontogenetically and perhaps sexu-
Figure 43. Sternarchorhynchus hagedornae sp. nov., holotype, sexually dimorphic male demonstrating modifica-
tions of dentary and dentary dentition, 249 mm total length, MUSM 30534; Peru, Madre de Dios, R?o Manu.
Figure 44. Sternarchorhynchus hagedornae sp. nov., female, approximately 192 mm total length, ANSP 180637;
Peru, Madre de Dios, Quebrada Pachija, R?o Manu.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 305
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
ally variable, but definite pattern uncertain because
of limited sample size. Anus and urogenital papilla in
smaller individual (162 mm TL) located at vertical
running two orbital diameters posterior of eye. Mid-
sized specimen (206 mm SL) with structures posi-
tioned slightly anterior of vertical through eye. Male
with definite patch of enlarged dentition on expanded
anterior portion of dentary (249 mm TL) with anus
and urogenital papilla more anteriorly positioned,
and located along vertical approximately one-quarter
of distance between anterior limit of orbit and tip of
snout. Combined opening for anus and urogenital
papilla longitudinally elongate.
Premaxilla of small size, somewhat rounded, with
five to eight teeth (N = 4). Dentary with two tooth
rows. Outer tooth row with five to six curved conical
teeth and inner tooth row with three to four teeth
(N = 3). Mature males with dentary expanded anteri-
orly and widened laterally into dorsally bulbous
region rounded from dorsal view, with expansion
bearing patch of enlarged dentition. Mouth terminal
with rictus in juveniles located slightly posterior to
vertical through anterior naris. Rictus in adults
shifted somewhat anteriorly and located anterior to
vertical through anterior naris.
Branchiostegal rays five; with first to third rays
relatively narrow and elongate and fourth and fifth
rays large and broad. Precaudal vertebrae 16?17 (13
anterior; three to four transitional; N = 4).
Pectoral-fin rays ii + 12?14 [ii + 14] (N = 6). Anal-fin
origin located slightly posterior of vertical through
anterior margin of opercle. Anterior unbranched anal-
fin rays 27?35 [27] (N = 6). Total anal-fin rays 173?
193 [173] (N = 6). Scales above lateral line at midbody
nine to 13 [13] (N = 6). Scales along mid-dorsal region
of body somewhat sparse and not readily apparent on
body surface. Origin of midsaggital electroreceptive
filament located approximately at 70% of TL. Fila-
ment in juveniles extending posteriorly to vertical one
scale posterior of vertical through posterior terminus
of base of anal fin; filament in adults reaching to
vertical through posterior terminus of base of anal fin.
Tail compressed and short, ending in small and
moderate caudal fin. Caudal-fin rays 12?16 [18]
(N = 6).
Coloration in alcohol: Overall ground coloration dark
brown. Series of whitish, papillae-like structures
broadly distributed over lateral and dorsal portions of
posterior two-thirds of snout, lateral surface of head,
and dorsalmost portion of body. Lightly coloured spots
limited to irregular single series to each side of elec-
troreceptive filament on posterior portion of body.
Snout with variably distinct, narrow band of darker
pigmentation extending anteriorly from region some-
what anterior of orbit; and reaching anterior portion
of snout in some individuals and apparent even in
overall darkly pigmented specimens. Band of dark
pigmentation forms lateral border of narrow, more
lightly coloured mid-dorsal band present on head.
Anterior portion of lightly coloured mid-dorsal stripe
on head less apparent in male with well-developed
patches of enlarged dentition on lower jaw. Body
pigmentation very slightly darker dorsally, but with
mid-dorsal more lightly coloured stripe continuous
with corresponding stripe on head and extending pos-
teriorly onto basal portions of electroreceptive
filament.
Pectoral fin dark in all specimens, with dark chro-
matophores overlying fin rays. All examined speci-
mens with anal fin dusky and posterior margin of fin
outlined by series of dark chromatophores. Caudal fin
dark overall, but with distal margin hyaline.
Distribution: All examined specimens of S. hagedor-
nae originated in the Manu Biosphere Reserve, in the
upper R?o Madeira basin in south-eastern Peru
(Fig. 42).
Ecology: Hagedorn & Keller (1996: 488, 490 493)
remarked that the type locality for S. hagedornae,
Quebrada Pachija, is an open-gallery, high flow
stream with a flow of 0.748 m/s, a mean stream depth
of 0.397 ? 0.059 m, and a mean stream width of
19.1 ? 1.0 m. According to these authors this species,
(their Sternarchorhynchus sp.) ?lived in the fastest
flowing water sampled; most adult specimens were
captured from a single rocky rapids?. Their collecting
efforts also yielded numerous fry and small juveniles
from within floating debris along the fast-flowing
edges of the R?o Manu that they considered to be the
same species. We have not examined these samples.
Electrical organ discharge: Sternarchorhynchus hage-
dornae was studied in the field by Hagedorn & Keller
(1996: 493, figs 2f, 4) who reported that it is a high
frequency, wave-type fish with peak-power EOD fre-
quencies ranging from 977?2832 Hz and a mean of
1608.5 ? 160.6 Hz SE in the 14 specimens examined.
They remarked on the variety of EOD types observed
in the species (Hagedorn & Keller, 1996: fig. 4), but
pointed out that they lacked sufficient specimens to
determine whether this variation reflected sexual
dimorphism in this feature; however, they did
comment that the heterogeneity might reflect changes
with ?age, sex and/or activity pattern?.
Secondary sexual dimorphism: The obvious sexually
dimorphic feature in S. hagedornae is the anteriorly
lengthened and transversely widened anterior portion
of the dentary in males and the associated patch of
enlarged, posteriorly recurved teeth on this region.
306 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
The male (249 mm TL) had the anus and urogenital
papilla more anteriorly positioned than did the
slightly shorter, possibly female, specimen (206 mm
TL) and the juveniles. In the male, the anus and the
urogenital papilla are located along the vertical
running approximately one-quarter of the distance
between the anterior limit of the orbit and the tip of
the snout. This position is distinctly anterior of the
location of the anus and urogenital papilla in smaller
specimens, in which these structures are positioned
from slightly anterior to variably posterior of the
vertical through the eye.
Etymology: The species name, hagedornae, is in
honour of Mary Hagedorn of the Smithsonian Insti-
tution who collected the type series and has made
many contributions to our understanding of the diver-
sity of gymnotiforms.
Material examined
Holotype: ? PERU. Madre de Dios: Manu Biosphere
Reserve, Quebrada Pachija, tributary emptying into
R?o Manu 3 km upstream of Pakitza (Pakitza at
11?55?48?S, 71?15?18?W), MUSM 30534, 1 (249, male);
collected by M. Hagedorn et al.
Paratypes: ? PERU. Madre de Dios: Manu Biosphere
Reserve, Quebrada Pachija, tributary emptying into
R?o Manu 3 km upstream of Pakitza (Pakitza at
11?55?48?S, 71?15?18?W), collected by M. Hagedorn
et al., with holotype, USNM 391574, 2 (169?206);
MUSM 30535, 1 (202); MBUCV 33742, 2 (162?194).
MUSM 23755, (174); Manu Biosphere Reserve, R?o
Los Amigos.
Nontype specimens: ? PERU. Cuzco: R?o Inambari and
mouth of Quebrada Hondonado, Madre de Dios drain-
age, upstream of Puerto Mazuko (13?06?23?S,
70?24?44?W), ANSP 180637, 2 (200?208).
STERNARCHORHYNCHUS HIGUCHII SP. NOV.
(FIGS 42, 45, 46; TABLE 8)
Diagnosis: Sternarchorhynchus higuchii is distin-
guished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical
through anterior nares, the presence of scales
although sometimes sparse and covered by skin
along the mid-dorsal region of the body to the origin
of the electroreceptive filament, the presence of an
obscure, more lightly coloured, narrow band of mid-
dorsal pigmentation on the head and anterior mid-
dorsal region of the body, the slightly dusky anal fin
without a distinct dark band along its distal margin,
the lateral line extending posteriorly to a point
approximately four to seven scales short of the base
of the anal fin, the possession of two rows of
dentary teeth with the outer row having nine to ten
teeth, 23?31 anterior unbranched anal-fin rays,
162?178 total anal-fin rays, eight to 12 scales above
the lateral line at the midbody, ten to 12 caudal-fin
rays, the caudal length (14.7?18.9% of LEA), and
the tail depth (5.9?7.5% of caudal length).
Description: Morphometric data for holotype and
paratypes in Table 8.
Lateral line falling short of base of caudal fin by
distance equal to four to seven scales and absent on
remainder of tail and on caudal fin. Snout elongate,
Figure 45. Sternarchorhynchus higuchii sp. nov., holotype, sexually dimorphic male demonstrating modifications of
dentary and dentary dentition, 246 mm total length, INPA 28358; Brazil, Amazonas, Cachoeira do Miriti, Rio Uatum?.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 307
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
compressed and slightly curved ventrally distally.
Posterior naris closer to tip of snout than to anterior
margin of orbit. Branchial opening restricted and
situated slightly anterior to vertical through pectoral-
fin origin. Location of anus and urogenital papilla
apparently sexually dimorphic. Anus and urogenital
papilla in smaller individuals and apparently mature
females located within area between vertical located
two orbital diameters posterior of orbit and vertical
running through eye. Males with definite patch of
enlarged dentition on dentary with anus and urogeni-
tal papilla more anteriorly positioned, located along
verticals two to four orbital diameters anterior of
anterior margin of eye (most anterior position
approximately one-quarter of distance between ante-
rior margin of orbit and tip of snout). Combined
opening for anus and urogenital papilla distinctly
elongate longitudinally.
Premaxilla of small size, somewhat rounded, with
seven to eight teeth (N = 5). Dentary with two tooth
rows with six curved conical teeth in outer row and
three to four teeth on inner row (N = 5) in juveniles
and females. Mature males demonstrating sexual
dimorphism in lower jaw with anterior portion of
dentary extending further anteriorly than in females
and juveniles and with dentary distinctly expanded
laterally into dorsally bulbous structure rounded from
dorsal view. Expanded portion of dentary bearing
series of enlarged, slightly posteriorly recurved teeth.
Mouth terminal in juveniles and females and some-
what dorsally directed in males with anteriorly and
transversely expanded dentaries. Rictus located
slightly anterior to vertical through anterior naris in
all specimens.
Branchiostegal rays five; with first to third rays
relatively narrow and elongate and remaining rays
large and broad. Precaudal vertebrae 15?16 (12?13
anterior; two to four transitional; N = 16).
Pectoral-fin rays ii + 11?13 [ii + 13] (N = 14). Anal-
fin origin located slightly posterior of vertical through
anterior margin of opercle. Anterior unbranched anal-
fin rays 23?31 [28] (N = 14). Total anal-fin rays 162?
178 [171] (N = 15). Scales above lateral line at
midbody eight to 12 [10] (N = 16). Scales along mid-
dorsal region of body present, but somewhat sparse
and not readily apparent on body surface. Origin of
midsaggital electroreceptive filament located approxi-
mately at 59% of TL. Filament in specimens of all
sizes extending six to eight scales posterior of vertical
through posterior terminus of base of anal fin. Tail
compressed and long, ending in very small, somewhat
elongate caudal fin. Caudal-fin rays ten to 12 [11]
(N = 11).
Coloration in alcohol: Overall ground coloration dark
brown. Snout with variably distinct, narrow band of
slightly darker pigmentation extending from region
somewhat in advance of eye to anterior portion of
snout. Second stripe of dark pigmentation running
ventrally on snout to lower jaw. Two dark stripes
delimit intermediate, more lightly pigmented region
running along lateral surface of snout. Dorsal band
of dark pigmentation forms lateral border of narrow,
lightly coloured, mid-dorsal band on head that ter-
minates posteriorly in region dorsal to eye. Body
pigmentation very slightly darker dorsally and
without distinct mid-dorsal lightly coloured stripe
present in that region in many congeners. Mid-
dorsal region of body irregularly less intensely pig-
mented in some individuals, but with these lighter
areas not confluent and not forming distinct, narrow
stripe.
Pectoral fin coloration dark in all specimens, with
dark chromatophores overlying fin rays. All examined
specimens with anal fin dusky and posterior margin
of fin-rays outlined by series of dark chromatophores.
Caudal fin dark overall, but with distal margin
hyaline.
Figure 46. Sternarchorhynchus higuchii sp. nov., female, 180 mm total length, INPA 20855; Brazil, Amazonas,
Cachoeira do Miriti, Rio Uatum?.
308 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
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(N
=
11
)
45
.0
M
ou
th
le
n
gt
h
5.
5
4.
9?
7.
3
(N
=
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)
5.
8
6.
7
4.
7?
8.
7
(N
=
6)
6.
9
6.
5
4.
3?
8.
4
(N
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)
6.
5
In
te
rn
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l
di
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an
ce
2.
8
2.
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4.
3
(N
=
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)
2.
7
3.
3
2.
3?
4.
1
(N
=
6)
2.
6
3.
1
2.
9
1.
9?
4.
2
(N
=
11
)
3.
1
E
ye
di
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3.
6
3.
1?
5.
2
(N
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)
4.
1
4.
1
3.
6?
5.
6
(N
=
6)
4.
7
4.
0
4.
0?
6.
3
(N
=
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)
5.
1
In
te
ro
cu
la
r
w
id
th
4.
7
3.
3?
12
.3
(N
=
11
)
7.
0
6.
9
5.
9?
8.
7
(N
=
6)
5.
9
7.
0
6.
6
6.
6?
10
.7
(N
=
11
)
8.
7
P
os
to
cu
la
r
di
st
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37
.0
35
.5
?4
2.
5
(N
=
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)
38
.8
33
.1
38
.0
?4
1.
1
(N
=
6)
39
.0
44
.7
41
.5
?4
9.
1
(N
=
11
)
44
.1
B
ra
n
ch
ia
l
op
en
in
g
10
.5
9.
6?
12
.3
(N
=
15
)
10
.9
12
.3
9.
4?
13
.4
(N
=
6)
10
.9
11
.7
12
.9
11
.4
?1
7.
9
(N
=
11
)
14
.1
P
er
ce
n
t
of
ca
u
da
l
le
n
gt
h
T
ai
l
de
pt
h
6.
1
5.
9?
7.
5
(N
=
11
)
6.
4
9.
1
8.
0?
11
.1
(N
=
4)
9.
6
16
.5
10
.1
?1
9.
2
(N
=
7)
15
.5
C
au
da
l-
fi
n
le
n
gt
h
10
.3
12
.5
?2
0.
6
(N
=
10
)
15
.2
23
.9
20
.1
?2
3.
6
(N
=
4)
22
.1
34
.1
17
.3
?4
6.
0
(N
=
7)
33
.9
S
ex
u
al
ly
di
m
or
ph
ic
fe
at
u
re
s
fo
r
S
.
in
pa
i
ar
e
pr
es
en
te
d
as
tw
o
en
tr
ie
s.
F
ir
st
en
tr
y
is
da
ta
fo
r
al
l
sp
ec
im
en
s
ot
h
er
th
an
se
xu
al
ly
di
m
or
ph
ic
m
at
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re
m
al
es
w
it
h
in
fo
rm
at
io
n
fo
r
se
xu
al
ly
di
m
or
ph
ic
m
al
e
in
se
co
n
d
en
tr
y
ba
se
d
on
on
e
sp
ec
im
en
of
22
2
m
m
to
ta
l
le
n
gt
h
.
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u
m
be
r
of
sp
ec
im
en
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in
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ca
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in
pa
re
n
th
es
es
.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 309
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Distribution: All examined specimens of S. higuchii
were collected at the Cachoeira do Miriti and Cach-
oeira do Morena in the Rio Uatum? in the eastern
portions of Amazonas, Brazil (Fig. 42).
Secondary sexual dimorphism: Mature males of S.
higuchii have an anteriorly extended and laterally
enlarged anterior portion of the dentary with the
associated patch of enlarged teeth. Males bearing
such elaborations of the lower jaw and dentary teeth
have the anus and urogenital papilla more anteriorly
positioned than in examined conspecifics of compa-
rable body sizes. Both the anus and urogenital papil-
lae in these males are located distinctly anterior of
the vertical through the eye, rather than at, or pos-
terior of, that position as in males lacking modified
dentaries and associated dentition. Females and juve-
niles similarly have these structures in a posterior
position. Examined females of S. higuchii with
mature ovaries are smaller than available males dem-
onstrating sexual dimorphism in the lower jaw and
dentary dentition.
Etymology: The species name, higuchii, is in honour
of Hor?cio Higuchi of the Museu Paraense Emilio
Goeldi, who provided invaluable assistance to the first
author during his early studies of gymnotiforms.
Remarks: Sternarchorhynchus higuchii was collected
at the same type locality as S. jaimei. The two species
differ in the posterior extent of the lateral line (falling
short of base of caudal fin by four to seven scales
versus reaching the base of the caudal fin, respec-
tively), total anal-fin rays (162?178 versus 180?195,
respectively), the pigmentation of the mid-dorsal
region of the body anterior to the origin of the elec-
troreceptive filament (dark versus with narrow,
lightly coloured stripe, respectively), and caudal
depth (5.9?7.5 versus 10.1?19.2% of caudal length,
respectively), and nearly completely in body depth
(8.7?11.0 versus 10.8?12.6 of LEA, respectively).
Material examined
Holotype: ? BRAZIL. Amazonas: Rio Uatum?, Cach-
oeira do Miriti, Presidente Figueredo (approximately
2?01?S, 59?28?W), INPA 28358 (246), collected by
E. Ferreira, R. Leite, and S. Kullander, 4.x.1987.
Paratypes: ? BRAZIL. Amazonas: Rio Uatum?, Cach-
oeira do Miriti, Presidente Figueredo (approximately
2?01?S, 59?28?W), collected by E. Ferreira, R. Leite,
and S. Kullander, with holotype, INPA 20855, 15
(88?243); USNM 391714, 1 (189).
Nontype specimens: ? BRAZIL. Amazonas: Rio
Uatum?, Cachoeira do Miriti (approximately 2?01?S,
59?28?W), INPA uncat., 2 (158?181). Rio Uatum?,
Cachoeira do Morena, INPA 20854, 25 (125?233).
STERNARCHORHYNCHUS INPAI SP. NOV.
(FIGS 42, 47, 48; TABLE 8)
Sternarchorhynchus oxyrhynchus Ferreira, 1995: 51
[Brazil, Par?, Rio Trombetas, Cachoeira Porteira].
Diagnosis: Sternarchorhynchus inpai is distinguished
from all congeners by having a very short first bran-
chiostegal ray that is distinctly shorter than the
second ray rather than being approximately subequal
in length to that ossification. It is furthermore differ-
entiated from all other species of Sternarchorhynchus
by possessing the following combination of characters:
a short gape that terminates posteriorly at, or slightly
short of, the vertical through the anterior nares, the
presence of a definite series of scales along the mid-
dorsal region of the body, the more lightly coloured
mid-dorsal stripe on the head sometimes extending
posteriorly to the vertical through the insertion of the
pectoral fin, the dusky anal fin, the very short first
branchiostegal ray, the possession of four to seven
Figure 47. Sternarchorhynchus inpai sp. nov., holotype, female, 191 mm total length, INPA 22895; Brazil, Par?,
Cachoeira Porteira, Rio Mapuera.
310 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
premaxillary teeth, five to six teeth in the outer row
of the dentary, 15 precaudal vertebrae, the distance
from the snout to the anus in mature males (13.4% of
LEA), the preanal distance (15.2?16.3% of LEA; 18.9
in mature male), the caudal length (12.6?15.6% of
LEA), the pectoral-fin length (27.9?42.3% of HL; 27.9
in mature male), the head depth at the eye in mature
males (26.3 of HL), the head depth at the nape
(40.5?48.6% of HL), the distance from the posterior
naris to the eye in mature males (59.7 of HL), the
postocular distance (33.1?41.1% of HL), the height of
the branchial opening (9.4?13.4% of SL; 10.9% in
mature males), the tail depth (8.0?11.1% of caudal
length), and the caudal-fin length (20.1?23.9% of
caudal length).
Description: Morphometric data for examined speci-
mens in Table 8.
Lateral line extending posteriorly to point four
scales anterior of base of caudal fin but absent on fin.
Snout elongate, compressed and slightly curved ven-
trally along anterior portion. Mouth terminal to very
slightly anterodorsally orientated and relatively
small with distinct fleshy pad at anterior of lower jaw.
Rictus located anterior to vertical through anterior
naris. Anus and urogenital papilla located ventral to
head, with position apparently ontogenetically vari-
able. Anus and urogenital papilla located along ver-
tical about one orbital diameter posterior of eye in
juveniles and along verticals through to one orbital
diameter anterior of eye in mature males and
females. Combined opening for anus and urogenital
papilla longitudinally ovoid in all specimens.
Premaxilla with four to seven teeth (N = 6) appar-
ent in whole specimens. Dentary with two tooth rows;
outer row with five to six teeth and inner row with
three teeth (N = 4).
Branchiostegal rays five; with first ray distinctly
shorter than second and first three rays narrow.
Fourth and fifth rays large and broad with fifth ray
branched distally on both sides in cleared and stained
specimen. Precaudal vertebrae 15 (13 anterior; two
transitional; N = 6).
Pectoral-fin rays ii + 12?13 (N = 7). Anal-fin origin
located anterior to opercle. Anterior unbranched anal-
fin rays 17?24 [17] (N = 3). Total anal-fin rays 156?
167 [161] (N = 7). Scales above lateral line at midbody
eight to 11 (N = 9). Scales present along mid-dorsal
line to origin of midsaggital electroreceptive filament.
Origin of midsaggital electroreceptive filament
located on posterior half of body, approximately at
60% of TL. Filament extending posteriorly three to
seven scales beyond vertical through posterior termi-
nus of base of anal fin. Tail compressed and moderate,
ending in small, elongate, pointed caudal fin. Caudal-
fin rays 13?16 [14] (N = 6).
Coloration in alcohol: Overall coloration brown. Head
dark brown overall other than for more lightly
coloured stripe along lateral surface of snout and very
narrow, lightly coloured mid-dorsal stripe on snout
that terminates posteriorly approximately at vertical
through eye. Body dark overall, somewhat more so
dorsally. Pectoral fin dusky with rays somewhat
darker than membranes. Anal fin dusky with rays
darker than membranes. Caudal fin dark with distal
regions somewhat lighter.
Distribution: Sternarchorhynchus inpai is only known
from the type locality at Cachoeira Porteira on the
Rio Mapuera, Par?, Brazil (Fig. 42).
Secondary sexual dimorphism: The single mature
examined male of S. inpai as evidenced by the well-
developed testes has a slightly longer snout than do
females of comparable sizes. This species matures at
relatively small body sizes with a 154 mm TL female
bearing well-developed eggs and the single mature
male being at least 222 mm (a portion of the caudal is
lacking in this specimen).
Etymology: The species name, inpai, is in reference to
the Instituto Nacional de Pesquisas da Amaz?nia
(INPA), in Manaus, Brazil, that has been the centre
for the study of the biodiversity of the Brazilian
Amazon for over five decades.
Figure 48. Sternarchorhynchus inpai sp. nov., paratype, male (tail broken), 222 mm total length, INPA 22899;
Brazil, Par?, Cachoeira Porteira, Rio Mapuera.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 311
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Remarks: Specimens reported as S. oxyrhynchus by
Ferreira (1995: 51) from Cachoeira Porteira have
proved to be S. inpai. Sternarchorhynchus inpai
occurs in the same river basin as S. mareikeae and
the two species have similar coloration patterns. They
differ in the numbers of teeth on the premaxilla (four
to seven versus 12?13, respectively), and in the outer
row of the dentary (five to six versus 12?13, respec-
tively), and the number of precaudal vertebrae (15
versus 16, respectively). Mature males of the two
species can be furthermore distinguished on various
sexually dimorphic morphometric features detailed in
tables 15 and 18 of Ferreira (1995), most notably the
distance from the snout to the anus (13.4% in S. inpai
versus 8.8?10.8% in S. mareikeae), the preanal dis-
tance (18.9 versus 12.7?15.2%, respectively), and the
height of the branchial opening (10.9 versus 12.3?
15.4%, respectively).
Material examined
Holotype: ? BRAZIL. Par?: Rio Mapuera, Cachoeira
Porteira, last fall before Rio Trombetas (approxi-
mately 1?05?S 57?02?W); collected by E. Ferreira and
M. J?gu, 19.iv.1985; INPA 22895, 191.0 mm TL,
female.
Paratypes: ? BRAZIL. Par?: Rio Mapuera, Cachoeira
Porteira, last fall before Rio Trombetas (approxi-
mately 1?05?S 57?02?W); collected with holotype by
E. Ferreira and M. J?gu, 19.iv.1985; INPA 22899, 10
(1 CS; 54?222); USNM 391715, 1 (195).
STERNARCHORHYNCHUS JAIMEI SP. NOV.
(FIGS 49, 50; TABLE 8)
Diagnosis: Sternarchorhynchus jaimei is distin-
guished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical
through the anterior nares, the absence of scales
along the mid-dorsal region of the body as far pos-
teriorly as the vertical through the posterior limit of
the pectoral fin, the presence of a narrow, more
lightly coloured band of mid-dorsal pigmentation on
the head and mid-dorsal region of the body extend-
ing posteriorly to the origin of the electroreceptive
filament and sometimes beyond that point, the
lateral line that extends to the base of the caudal
fin, the presence of four to seven premaxillary teeth,
23?26 anterior unbranched anal-fin rays, and 180?
195 total anal-fin rays, the distance from the anus
to the anal-fin insertion (4.8?12.3% of HL), the dis-
tance from the posterior naris to the snout (8.1?
12.9% of HL), the head width (22.7?28.9% of HL),
the head depth at the nape (41.8?43.2% of HL), the
interocular distance (6.6?10.7% of HL), the postocu-
lar distance (41.5?49.1% of HL), the height of the
branchial opening (11.4?17.9% of HL), the postocu-
lar distance (41.5?58.7% of HL), the pectoral-fin
length (35.7?58.4% of HL), the caudal depth (10.1?
19.2% of caudal length), and the caudal-fin length
(17.3?46.0% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 8.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
slightly curved ventrally along anterior portion; cur-
vature more pronounced in larger individuals. Mouth
terminal. Dentary with distinct fleshy pad anteriorly.
Rictus located anterior to vertical through anterior
naris. Anus and urogenital papilla located ventral to
head, with position apparently ontogenetically vari-
able. Anus and urogenital papilla located along vertical
about two orbital diameters posterior of eye in juve-
niles and along vertical through eye in larger speci-
mens. Combined opening for anus and urogenital
papilla ranging from circular to longitudinally ovoid.
Premaxilla with four to seven teeth (N = 5) appar-
ent in whole specimens. Dentary with two tooth rows;
outer row with eight to nine teeth and inner row with
two to three teeth (N = 5).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16 (12?13 anterior;
three to four transitional; N = 12).
Figure 49. Sternarchorhynchus jaimei sp. nov., holotype, female, 200 mm total length, INPA 28359; Brazil, Ama-
zonas, Cachoeira do Miriti, Rio Uatum?.
312 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Pectoral-fin rays ii + 11?14 [ii + 11] (N = 12). Anal-
fin origin located anterior to opercle. Anterior
unbranched anal-fin rays 23?36 [25] (N = 12). Total
anal-fin rays 180?195 [184] (N = 7). Scales above
lateral line at midbody nine to 12 [12] (N = 12).
Scales along mid-dorsal midline of body absent or
sparse to midlength of body in smaller specimens,
and absent in larger specimen as far posteriorly as
vertical through posterior limit of pectoral fin, then
sparse to midlength of body and followed by
regular series of scales as far posteriorly as
origin of midsaggital electroreceptive filament.
Origin of midsaggital electroreceptive filament
located on posterior half of body, at point approxi-
mately 65% of TL. Filament extending posteriorly
four to six scales anterior of vertical through poste-
rior terminus of base of anal fin. Tail compressed
and short, ending in small, somewhat rounded
caudal fin in juveniles and in small, somewhat lan-
ceolate fin in large individuals. Caudal-fin rays
11?18 [14] (N = 7).
Coloration in alcohol: Overall coloration of head and
body brown. Head with variably intense band of dark
pigmentation extending along dorsolateral surface of
snout nearly to tip of snout. Ventrolateral portion of
snout dark. Two dark bands on snout border inter-
mediate more lightly coloured region on anterior half
of snout. Dorsal band of dark coloration forms lateral
margin of narrow, lightly coloured stripe extending
from tip to snout to varying degrees beyond vertical
through eye and onto mid-dorsal postocular portion of
head. Stripe on head variably obscurely continuous
with narrow, lightly coloured mid-dorsal stripe on
body. Mid-dorsal stripe on body extending posteriorly
to origin of electroreceptive filament. Pectoral fin
dusky with rays somewhat darker than membranes.
Anal fin dusky with rays darker than membranes.
Caudal fin dark with distal regions somewhat lighter.
Distribution: Sternarchorhynchus jaimei is only
known from the Rio Uatum?, Amazonas, Brazil
(Fig. 50).
Figure 50. Map of central and northern South America showing geographical distribution of Sternarchorhynchus jaimei
(1 = holotype locality), Sternarchorhynchus kokraimoro sp. nov. (2 = holotype locality), Sternarchorhynchus
mareikeae sp. nov. (3 = holotype locality), Sternarchorhynchus marreroi sp. nov. (4 = holotype locality), and
Sternarchorhynchus mendesi sp. nov. (5 = holotype locality) (some symbols represent more than one locality and/or lot
of specimens).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 313
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Secondary sexual dimorphism: No sexual dimorphism
was apparent in the examined samples of S. jaimei.
Etymology: The species name, jaimei, is in honour of
Jaime Ribeiro Carvalho J?nior, of the Centro do
Jovem Aquarista, in recognition of his invaluable
assistance to the first author during the early phases
of his studies of gymnotiforms.
Remarks: One of the examined specimens, a female of
115 mm TL, had clearly developing eggs and it seems
likely that the species matures at relatively small
body sizes. Sternarchorhynchus jaimei was collected
at the same type locality as S. higuchii. The species
differ in various details of pigmentation, meristics,
and morphometrics detailed in Remarks under
S. higuchii.
Material examined
Holotype: ? BRAZIL. Amazonas: Rio Uatum?, Cach-
oeira do Miriti, Presidente Figueredo (approximately
2?01?S, 59?28?W), collected by E. Ferreira, R. Leite,
and S. Kullander, 4.x.1987; INPA 28359 (200, matur-
ing female).
Paratypes: ? BRAZIL. Amazonas: Rio Uatum?, Cach-
oeira do Miriti, Presidente Figueredo (approximately
2?01?S, 59?28?W), collected with holotype by E. Fer-
reira, R. Leite, and S. Kullander, 4.x.1987; INPA
22902, 2 (72.2?75.6). Rio Uatum?, Cachoeira Morena,
Presidente Figueredo, collected by E. Ferreira, R.
Leite, and S. Kullander, 7.x.1987; INPA 26122, 10
(one cleared and stained, 88?123); USNM 391716, 1
(127).
STERNARCHORHYNCHUS KOKRAIMORO SP. NOV.
(FIGS 50?52; TABLE 9)
Diagnosis: Sternarchorhynchus kokraimoro is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
along the mid-dorsal region of the body, the absence of
a more lightly coloured narrow band of mid-dorsal
pigmentation on the head and mid-dorsal region of
the body anterior of the origin of the electroreceptive
filament, the dusky anal fin, the termination of the
lateral line three to five scales anterior of the base of
the caudal fin, the possession of seven to ten premax-
illary teeth, two tooth rows on the dentary with eight
to ten teeth in the outer row, 175?177 total anal-fin
rays, eight to nine scales above the lateral line at the
midbody, 16?17 precaudal vertebrae, 15 caudal-fin
rays, the distance from the snout to the anus (13.6?
15.0% of LEA), the preanal distance (16.9?17.1% of
LEA), the prepectoral-fin distance (23.1?24.0% of
LEA), the head length (22.9?23.1% of LEA), the
caudal length (14.3?15.5% of LEA), the distance from
the anus to the anal-fin insertion (8.2?12.5% of HL),
the head width (18.6?20.2% of HL), the snout length
(63.7?66.2% of HL), and the interocular distance (4.6?
5.1% of HL).
Figure 51. Sternarchorhynchus kokraimoro sp. nov., holotype, male, showing deeper snout of males, 197 mm total
length, INPA 28360; Brazil, Par?, Cachoeira de Kaituk?, Rio Xingu.
314 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Description: Morphometric data for examined speci-
mens in Table 9.
Lateral line extending posteriorly to point approxi-
mately three to five scales anterior of base of caudal
fin but absent on remainder of tail and on fin. Snout
elongate, compressed and curved ventrally distally.
Male with dorsomedial fleshy ridge on anterior half of
snout; ridge absent in female. Ridge makes that
portion of snout of male overall distinctly deeper than
in female (compare Figs 51, 52). Mouth moderate,
with opening anterodorsally orientated, and rictus
located at, or slightly posterior of, vertical through
anterior naris. Dentary in mature male lengthened
anteriorly, slightly expanded transversely and
bearing patch of somewhat enlarged teeth. Anus and
urogenital papilla located ventral to head, with posi-
tion apparently sexually dimorphic in limited avail-
able sample. Anus and urogenital papilla positioned
along vertical through eye in mature female and
slightly more anteriorly in single mature male. Com-
bined opening for anus and urogenital papilla ovoid in
both sexes.
Premaxilla with seven to ten teeth (N = 2) apparent
in whole specimens. Dentary with two tooth rows;
outer row with eight to ten teeth and inner row with
two to three teeth (N = 2).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16?17 (14 anterior;
two to three transitional; N = 2).
Pectoral-fin rays ii + 12?13 [ii + 13] (N = 2). Anal-fin
origin located anterior to vertical through margin of
opercle. Anterior unbranched anal-fin rays 22?23 [23]
(N = 2). Total anal-fin rays 175?177 [175] (N = 2).
Scales above lateral line at midbody eight to nine [9]
(N = 2). Scales clearly present along mid-dorsal line to
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located
approximately at 64% of TL. Filament extending pos-
teriorly to vertical located two scales posterior of
vertical through terminus of base of anal fin. Tail
compressed and moderate, ending in small, elongate
caudal fin. Caudal-fin rays 15 [15] (N = 2).
Coloration in alcohol: Overall coloration of head and
body dark brown. Snout dark overall with stripe of
distinctly darker pigmentation extending from orbit
anteriorly to, or nearly to, tip of snout. Ventral
portion of snout darkly pigmented; that pigmentation
along with dark pigmentation on dorsolateral portion
of snout delimits intermediate, more lightly coloured
band running along lateral surface of snout. Head
and body uniformly dark along mid-dorsal region
contrary to condition present in many congeners. Pec-
toral fin distinctly dusky with rays covered with
small, dark chromatophores. Anal fin slightly dusky,
with rays overlain by spots of dark pigmentation.
Caudal fin dark overall, but with distal most margin
hyaline.
Distribution: Sternarchorhynchus kokraimoro is only
known from the Cachoeira de Kaituk? in the Rio
Xingu (Fig. 50).
Ecology: Little information is available about the type
locality of S. kokraimoro other than that it was a
rapids area in the northern portions of the Rio Xingu
(also Campos-da-Paz, 1999).
Figure 52. Sternarchorhynchus kokraimoro sp. nov., paratype, female, 171 mm total length, INPA 3932; Brazil,
Par?, Cachoeira de Kaituk?, Rio Xingu.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 315
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Secondary sexual dimorphism: The single examined
male of S. kokraimoro has the lower jaw lengthened
and somewhat expanded laterally, albeit to a lesser
degree than that in congeners that share this sexually
dimorphic feature. The available material of the
species does not permit us to determine whether the
lesser degree of development of this feature is char-
acteristic of S. kokraimoro or alternatively may rep-
Table 9. Morphometric data for holotype (H), and paratypes of Sternarchorhynchus kokraimoro, Sternarchorhynchus
mareikeae, and Sternarchorhynchus marreroi
S. kokraimoro S. mareikeae S. marreroi
H Paratype H Paratypes Mean H Paratypes Mean
Total length (mm) 197 171 192 131?221 (N = 9) ? 182 231?278 (N = 2) ?
Length to end of anal
fin (mm)
172 148 165 120?192 (N = 9) ? 166 209?252 (N = 2) ?
Head length (mm) 39.4 34.2 31.2 25.8?35.1 (N = 9) ? 27.1 34.3?41.3 (N = 2) ?
Caudal length (mm) 26.7 21.2 22.1 19.8?27.8 (N = 8) ? 14.6 22.8?26.4 (N = 2) ?
Per cent of length to end of anal fin
Anal-fin base 86.0 85.1 85.4 82.0?86.9 (N = 9) 85.1 85.5 88.4?92.3 (N = 2) 90.4
Distance snout to anus 13.6 15.0 9.6 8.8?13.5 (N = 9)
8.8?10.8
11.4
9.7
9.0 5.8?7.7 (N = 2) 6.7
Preanal-fin distance 16.9 17.1 13.9 12.2?17.8 (N = 9)
12.7?15.2
15.2
13.7
10.8 9.2?10.1 (N = 2) 9.7
Prepectoral-fin distance 24.0 23.1 19.0 17.9?23.1 (N = 9)
37.5?40.9
20.6
39.1
17.6 17.0?17.0 (N = 2) 17.0
Greatest body depth 10.1 12.3 10.0 10.9?13.6 (N = 9)
10.9?11.8
11.9
11.2
13.4 11.2?14.1 (N = 2) 12.6
Head length 22.9 23.1 18.9 18.3?23.2 (N = 9)
18.3?20.2
20.6
19.11
16.6 16.4?16.4 (N = 2) 16.4
Caudal length 15.5 14.3 13.4 13.4?17.4 (N = 8) 15.6 8.8 10.4?10.9 (N = 2) 10.6
Per cent of head length
Anus to anal-fin insertion 12.5 8.2 73.7 66.9?78.3 (N = 9) 73.5 10.1 16.2?17.6 (N = 2) 16.9
Pectoral-fin length 31.0 31.1 38.5 35.0?40.9 (N = 9)
37.5?40.9
38.6 47.5 52.0?75.8 (N = 2) 63.9
Head depth at eye 26.3 26.7 30.0 28.7?38.4 (N = 9)
29.9?38.4
32.5
33.5
32.9 34.1?35.4 (N = 2) 34.8
Head depth at nape 43.6 46.3 49.5 45.1?53.4 (N = 9) 49.5 62.6 55.1?65.5 (N = 2) 60.3
Head width 20.2 18.6 24.4 19.7?25.4 (N = 9) 22.5 29.9 25.9?28.7 (N = 2) 27.3
Snout length 66.2 63.7 61.0 51.2?65.4 (N = 9) 60.9 62.4 62.3?63.6 (N = 2) 62.9
Posterior naris to snout 8.3 7.4 ? ? ? 7.8 6.4?7.9 (N = 2) 7.2
Posterior naris to eye 55.0 55.0 50.5 48.2?53.7 (N = 9)
52.3?53.7
51.8
52.9
48.8 50.7?53.4 (N = 2) 52.1
Mouth length 6.5 5.9 6.8 4.3?9.4 (N = 9) 5.7 7.0 5.3?6.4 (N = 2) 5.8
Internarial distance 1.8 2.0 3.1 2.9?4.6 (N = 9)
3.2?3.5
3.5
3.4
4.3 3.0?3.5 (N = 2) 3.3
Eye diameter 3.9 3.8 4.8 3.5?5.3 (N = 9) 4.5 4.5 3.3?4.4 (N = 2) 3.9
Interocular width 5.1 4.6 9.0 6.6?8.1 (N = 9)
6.6?7.4
7.3
7.0
8.1 6.8?8.1 (N = 2) 7.4
Postocular distance 38.8 37.6 37.7 36.0?41.3 (N = 9) 38.6 49.0 45.3?45.4 (N = 2) 45.4
Branchial opening 12.0 12.1 10.9 11.9?15.4 (N = 9)
12.3?15.4
12.9
13.2
15.3 15.6?19.6 (N = 2) 17.6
Per cent of caudal length
Tail depth 10.1 12.3 9.7 7.1?10.2 (N = 9) 8.8 20.2 15.7?19.2 (N = 2) 17.5
Caudal-fin length 19.8 22.5 ? 18.5?24.7 (N = 7) 20.8 39.0 32.4 (N = 1) ?
Sexually dimorphic features for Sternarchorhynchus mareikeae are presented as two entries. First entry is data for all
specimens other than sexually dimorphic mature males with information for sexually dimorphic male in second entry
based on four specimens of 176?221 mm total length. Number of specimens indicated in parentheses.
316 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
resent ontogenetic variation or seasonality in the
expression of that modification. The male also has a
well-developed, mid-dorsal fleshy ridge along the
anterior half of the snout that is lacking in the female
(compare Figs 51, 52). This feature is unique to this
species within Sternarchorhynchus.
Etymology: The species name, kokraimoro, is in ref-
erence to the Kokraimoro, a group within the Kayabo
tribe whose ancestral lands included the type locality
of the species.
Material examined
Holotype: ? BRAZIL. Par?: Rio Xingu, Cachoeira de
Kaituk?, at Altamira (3?12?S, 52?12?W), collected by
L. Rapp Py-Daniel and J. A. Zuanon, 9.x.1990; INPA
28360 (197, mature male).
Paratype: ? BRAZIL. Par?: Rio Xingu, Cachoeira
de Kaituk?, Altamira (3?12?S, 52?12?W), collected
with holotype by L. Rapp Py-Daniel and J. A.
Zuanon, 9.x.1990; INPA 3932, 1 (171, mature
female).
STERNARCHORHYNCHUS MAREIKEAE SP. NOV.
(FIGS 50, 53, 54; TABLE 9)
Sternarchorhynchus oxyrhynchus, Ferreira, 1995: 51
[in listing of species from Brazil, Rio Trombetas, Par?,
Cachoeira Porteira].
Diagnosis: Sternarchorhynchus mareikeae is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the lateral line that extends posteriorly to
the base of caudal fin, the presence of a definite series
of scales along the mid-dorsal region of the body, the
presence of a narrow, more lightly coloured mid-
dorsal stripe on the head with the stripe sometimes
extending posteriorly along the body to the vertical
through the insertion of the pectoral fin, the dark
anal fin, the possession of 12?13 teeth in the outer
row of the dentary, 12?13 teeth in the outer row of the
dentary with a total of 16?17 teeth on that jaw,
159?181 total anal-fin rays, nine to 11 scales above
the lateral line at the midbody, 16 precaudal verte-
brae, the distance from the snout to the anus in
mature males (8.8?10.8% of LEA), the preanal dis-
tance (12.2?17.8% of LEA; 12.2?15.2% in mature
Figure 53. Sternarchorhynchus mareikeae sp. nov., holotype, male, 192 mm total length, INPA 22896; Brazil, Par?,
Cachoeira Porteira, Rio Mapuera.
Figure 54. Sternarchorhynchus mareikeae sp. nov., paratype, female, 135 mm total length, INPA 22901; Brazil,
Par?, Cachoeira Porteira, Rio Mapuera.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 317
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
males), the caudal length (13.4?17.4% of LEA), the
head length (18.3?23.2% of LEA), the prepectoral-fin
distance (17.9?23.1% of LEA), the postocular distance
(36.0?41.3% of HL), the pectoral-fin length (35.0?
40.9% of HL; 37.5?40.9% in mature males), the head
depth at the eye in mature males (29.9?38.4% of HL),
the head depth at the nape (45.1?53.4% of HL), the
distance from the posterior naris to the eye in mature
males (52.3?53.7% of HL), the eye diameter (3.5?5.3%
of HL), the interocular width (6.6?9.0% of HL), the
postocular distance (36.0?41.3% of HL), the height of
the branchial opening in mature males (12.3?15.4% of
HL), the tail depth (7.1?10.2% of caudal length), and
the caudal-fin length (18.5?24.7% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 9.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
slightly curved ventrally along anterior portion.
Mouth terminal to very slightly anterodorsally orien-
tated and relatively small with distinct fleshy pad at
anterior of lower jaw. Rictus located anterior to ver-
tical through anterior naris. Anus and urogenital
papilla located ventral to head and along vertical
about three orbital diameters anterior of eye in both
mature males and females. Combined opening for
anus and urogenital papilla longitudinally ovoid in all
specimens.
Premaxilla with 12?13 teeth (N = 7) apparent in
whole specimens. Dentary with two tooth rows; outer
row with 12?13 teeth and inner row with three to four
teeth (N = 5).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16 (12 anterior; four
transitional; N = 9).
Pectoral-fin rays ii + 10?12 [ii + 12] (N = 10). Anal-
fin origin located anterior to opercle. Anterior
unbranched anal-fin rays 15?26 [23] (N = 8). Total
anal-fin rays 159?181 [170] (N = 10). Scales above
lateral line at midbody nine to 11 [9] (N = 10). Scales
present along mid-dorsal line to origin of midsaggital
electroreceptive filament. Origin of midsaggital elec-
troreceptive filament located on posterior half of body,
approximately at 60% of TL. Filament extending pos-
teriorly four to seven scales beyond vertical through
posterior terminus of base of anal fin. Tail compressed
and moderate, ending in small, elongate, pointed
caudal fin. Caudal-fin rays 12?14 (N = 6).
Coloration in alcohol: Overall coloration brown. Head
dark brown overall laterally other than for more
lightly coloured stripe extending along lateral surface
of snout. Darker coloration anterior of eye along
dorsal surface of snout forms lateral margin of very
narrow, lightly coloured mid-dorsal stripe along snout
that terminates in rear portion of head. Body dark
overall, somewhat more so dorsally. Pectoral fin dusky
with rays somewhat darker than membranes. Anal fin
dusky with rays darker than membranes. Caudal fin
dark.
Distribution: Sternarchorhynchus mareikeae is only
known from the type locality at Cachoeira Porteira
along the Rio Mapuera, Par?, Brazil (Fig. 50).
Secondary sexual dimorphism: Sternarchorhynchus
mareikeae is possibly sexually dimorphic in terms of
body size. Mature females(N = 5) reach a maximum of
160 mm TL, whereas mature males collected with
those specimens attain a maximum of 221 mm TL.
This species matures at relatively small body sizes as
indicated by a 131 mm TL female filled with well-
developed eggs and a 176 mm TL male with mature
testes.
Etymology: The species name, mareikeae, is in honour
of the German biologist Mareike Roeder who has
greatly added to the senior author?s life.
Remarks: Examination of the specimens cited from
Cachoeira Porteira as S. oxyrhynchus by Ferreira
(1995: 51) has shown that some are rather S.
mareikeae. Sternarchorhynchus mareikeae occurs in
the same river basin as S. inpai and the two species
have similar coloration patterns. They differ both in
the numbers of teeth in the upper and lower jaws and
also in the various features involving mature males
that were cited in the Diagnosis and summarized
under Remarks for S. inpai.
Material examined
Holotype: ? BRAZIL. Par?: Rio Trombetas, Cachoeira
Porteira, last fall before Rio Trombetas (approxi-
mately 1?05?S 57?02?W), collected by E. Ferreira and
M. J?gu, 19.iv.1985; INPA 22896, 192.0 mm TL, male.
Paratypes: ? BRAZIL. Par?: Rio Trombetas, Cachoeira
Porteira, last fall before Rio Trombetas (approxi-
mately 1?05?S 57?02?W), collected by E. Ferreira and
M. J?gu, 19.iv.1985, INPA 22901, 9 (60?120, one
specimen cleared and stained); INPA 22900, 3 (125?
148); USNM 391717, 1 (177).
STERNARCHORHYNCHUS MARREROI SP. NOV.
(FIGS 50, 55; TABLE 9)
Diagnosis: Sternarchorhynchus marreroi is distin-
guished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical
318 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
through the anterior nares, the presence of a defi-
nite series of scales along the mid-dorsal region of
the body, the presence of a more lightly coloured
narrow band of mid-dorsal pigmentation on the
head and mid-dorsal region of the body extending
posteriorly to the origin of the electroreceptive fila-
ment and sometimes beyond that point, the hyaline
anal fin with slight dusky pigmentation distally in
some specimens, the extension of the lateral line
posteriorly to a point four to five scales anterior of
the base of the caudal fin, the possession of eight
premaxillary teeth, two rows of teeth on the dentary
with eight teeth in the outer row, 14 caudal-fin rays,
15 precaudal vertebrae, 21?31 anterior unbranched
anal-fin rays, 162?181 total anal-fin rays, ten to 11
scales above the lateral line at the midbody, 14
caudal-fin rays, the greatest body depth (11.2?14.1%
of LEA), the distance from the snout to the anus
(5.8?9.0% of LEA), the distance from the anus to
the anal-fin insertion (10.1?17.6% of HL), the
preanal distance (9.2?10.8% of LEA), the
prepectoral-fin distance (17.0?17.6% of LEA),
the head length (16.4?16.6% of LEA), the caudal
length (8.8?10.9% of LEA), the distance from the
posterior naris to the snout (6.4?7.9% of HL), the
head width (25.9?29.9% of HL), the pectoral-fin
length (45.7?75.8% of HL), the head depth at the
eye (32.9?35.4% of HL), the head depth at the nape
(55.1?65.5% of HL), the snout length (62.3?63.6% of
HL), the distance from the posterior naris to the eye
(48.8?53.4% of HL), the internarial distance (3.0?
4.3% of HL), the interocular width (6.8?8.1% of HL),
the height of the branchial opening (15.3?19.6% of
HL), the postocular distance (45.3?49.0% of HL),
and the tail depth (15.7?20.2% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 9.
Lateral line extending posteriorly to point approxi-
mately four or five scales short of base of caudal fin,
but absent on remainder of tail and fin. Snout elon-
gate, compressed and distinctly curved ventrally.
Mouth terminal and relatively small, with rictus
located slightly posterior to vertical through posterior
naris. Anus and urogenital papilla located ventral to
head, with position apparently ontogenetically some-
what variable. Openings positioned along vertical
slightly posterior of rear margin of eye in smaller
specimens and along vertical two orbital diameters
anterior of anterior margin of orbit in larger individu-
als. Combined opening for anus and urogenital
papilla longitudinally ovoid.
Premaxilla with eight teeth (N = 2) apparent in
whole specimens. Dentary with two tooth rows; outer
row with eight teeth and inner row with three teeth
(N = 2).
Branchiostegal rays five; with first three rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15 (12?13 anterior;
two to three transitional; N = 3).
Pectoral-fin rays ii + 12?13 [ii + 12] (N = 3). Anal-fin
origin located anterior to vertical through margin of
opercle. Anterior unbranched anal-fin rays 21?31 [30]
(N = 3). Total anal-fin rays 162?181 [162] (N = 3).
Scales above lateral line at midbody ten to 11 [10]
(N = 3). Scales present along mid-dorsal line to origin
of midsaggital electroreceptive filament. Origin of
midsaggital electroreceptive filament located approxi-
mately at 60% of TL. Filament extending posteriorly
to point two to five scales anterior of vertical through
posterior terminus of base of anal fin. Tail compressed
and short, ending in small, moderate, pointed caudal
fin. Caudal-fin rays 14 [14] (N = 2).
Coloration in alcohol: Overall coloration ranging from
light to medium brown, but missing on some regions
because of apparent postmortem damage. Head with
narrow stripe of slightly darker pigmentation extend-
ing anteriorly from orbit for distance a half to two-
thirds length of snout. Darker pigmentation forms
lateral margin of lightly coloured mid-dorsal stripe on
Figure 55. Sternarchorhynchus marreroi sp. nov., holotype, presumably female, 182 mm total length, MBUCV
15806; Venezuela, Apure, R?o Apure.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 319
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
snout. Lightly coloured stripe expands posteriorly
into longitudinally elongate ovoid, lightly coloured
area located above postocular portion of head. Ovoid
region continuous posteriorly with mid-dorsal, lightly
coloured stripe on body that extends posteriorly for
varying degrees towards origin of electroreceptive
filament. Pectoral fin dark distally and dorsally. Anal
fin hyaline overall, but with distal portions slightly
dusky in largest examined specimen. Caudal fin
dusky to dark.
Distribution: Sternarchorhynchus marreroi is known
from the central and delta regions of the R?o Orinoco
(Fig. 50).
Secondary sexual dimorphism: No sexual dimorphism
is apparent in the limited available samples of S.
marreroi.
Etymology: The name, marreroi, is in honour of
Cr?spulo Marrero of the Universidad Nacional Experi-
mental de los Llanos Occidentales, who has greatly
contributed to our knowledge of the biology of gym-
notiforms in Venezuela.
Material examined
Holotype: ? VENEZUELA. Apure: R?o Apure, in front
of Isla Apurito, left bank (8?00?N, 67?31?W), collected
by O. Castillo and F. Provenzano, 25.i.1984; MBUCV
15806 (182).
Paratypes: ? VENEZUELA. Apure: R?o Apure, in front
of Isla Apurito, left bank (8?00?N, 67?31?W), collected
with holotype by O. Castillo and F. Provenzano,
25.i.1984; MBUCV 33750, 1 (278; formerly MBUCV
V-15806, in part). Delta Amacuro: R?o Orinoco, south
of Isla Portuguesa (approximately 8?37?N, 61?49?W),
collected by J. G. Lundberg et al., 20.ii.1978; MBUCV
10637, 1 (231).
STERNARCHORHYNCHUS MENDESI SP. NOV.
(FIGS 50, 56; TABLE 10)
Diagnosis: Sternarchorhynchus mendesi is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, having the scales along the mid-dorsal
portion of the body anterior to the origin of the
electroreceptive filament sparse and covered by skin,
the presence of a more lightly coloured narrow band
of mid-dorsal pigmentation on the head and mid-
dorsal region of the body anterior of the origin of the
electroreceptive filament and sometimes posterior of
that point, the extension of the mid-dorsal filament to
a point approximately two to three scales beyond the
vertical through the posterior terminus of the anal
fin, the lateral line that extends to the base of the
caudal fin, the possession of ten to 11 teeth in the
outer row of the dentary, 29?37 anterior unbranched
anal-fin rays, 174?182 total anal-fin rays, six to seven
scales above the lateral line at the midbody, 12?17
caudal-fin rays, the length of the base of the anal fin
(80.8?85.9% of LEA), the caudal length (8.8?11.1% of
LEA), the length of the pectoral fin (33.9?44.2% of
HL), the postocular distance (38.8?40.8% of HL), the
distance from the posterior naris to the eye (46.6?
55.3% of HL), the height of the branchial opening
(10.2?14.1% of HL), and the tail depth (15.1?20.7% of
caudal length).
Description: Morphometric data for examined speci-
mens in Table 10.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
straight overall, but slightly curved ventrally along
anterior portion. Mouth slightly anterodorsally
directed, with fleshy process at anterior limit of
dentary. Rictus located along vertical ranging from
slightly anterior of, to slightly posterior of, anterior
naris. Anus and urogenital papilla located ventral to
head, with position ontogenetically variable. Open-
ings located along vertical approximately three
orbital diameters posterior of eye in smaller speci-
mens and maximum of one eye diameter anterior of
orbit in largest specimens. Combined opening for
anus and urogenital papilla ranging from circular to
longitudinally ovoid.
Figure 56. Sternarchorhynchus mendesi sp. nov., holotype, presumably female, 155 mm total length, MCNG 29129;
Venezuela, Monagas, R?o Guanipa.
320 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Premaxilla with six to nine teeth (N = 4) apparent
in whole specimens. Dentary with two tooth rows;
outer row with ten to 11 teeth and inner row with
three teeth (N = 4).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15?16 (12 anterior;
three to four transitional; N = 8).
Pectoral-fin rays ii + 10?14 [ii + 14] (N = 8). Anal-fin
origin located anterior to opercle. Anterior
unbranched anal-fin rays 29?37 [33] (N = 8). Total
anal-fin rays 174?182 [176] (N = 8). Scales above
lateral line at midbody six to nine [9] (N = 8). Scales
along mid-dorsal region of body sparse and covered by
thick skin. Origin of midsaggital electroreceptive fila-
ment located on posterior half of body situated
approximately at 55% of TL. Filament extending pos-
teriorly to within area delimited anterior by vertical
through posterior terminus of base of anal fin and
posteriorly by vertical two to three scales beyond that
landmark. Tail compressed and short, ending in
small, caudal fin with posteroventrally angled oblique
margin. Caudal-fin rays 12?17 [12] (N = 5).
Coloration in alcohol: Overall coloration of head and
body of specimens brown to dark brown. Snout dark
overall on lateral surface with little or no indication of
somewhat lighter central band present along at least
anterior one-third of snout in some congeners. Dark
pigmentation on lateral surface of snout forms lateral
margin of narrow, lightly coloured stripe running
along mid-dorsal region of snout. Lightly coloured
mid-dorsal stripe continues onto, and expands later-
ally on, postocular portion of head. Expanded lightly
coloured mid-dorsal region on rear of head continuous
posteriorly with narrow, lightly coloured mid-dorsal
Table 10. Morphometric data for holotype (H), and paratypes of Sternarchorhynchus mendesi, Sternarchorhynchus
mesensis, and Sternarchorhynchus montanus
S. mendesi S. mesensis S. montanus
H Paratypes Mean H Range Mean H Paratype
Total length (mm) 155 77.7?192 ? 249 116?228 (N = 8) ? 226 258
Length to end of anal
fin (mm)
142 70.4?146 ? 226 106?209 (N = 8) ? 221 233
Head length (mm) 29.9 16.9?35.5 ? 46.5 23.2?38.8 (N = 10) ? 37.7 38.0
Caudal length (mm) 13.8 6.2?15.3 ? 23.0 10.0?27.0 (N = 8) ? 5.25 7.23
Per cent of length to end of anal fin
Anal-fin base 82.4 80.8?85.9 (N = 5) 84.2 88.0 83.0?88.0 (N = 8) 85.2 85.0 90.9
Distance snout to anus 12.5 11.3?16.2 (N = 6) 13.3 ? 13.5?15.2 (N = 3) 14.4 7.3 6.9
Preanal-fin distance 15.2 13.2?18.2 (N = 5) 15.1 14.4 14.2?17.0 (N = 8) 15.6 10.2 9.5
Prepectoral-fin distance 21.3 20.0?23.8 (N = 5) 21.3 21.4 21.5?23.8 (N = 8) 22.4 16.6 10.9
Greatest body depth 11.5 7.4?12.9 (N = 5) 10.6 10.4 10.0?12.3 (N = 8) 10.9 7.5 13.0
Head length 21.4 19.5?24.0 (N = 5) 21.0 20.5 20.5?23.6 (N = 8) 21.8 17.0 16.3
Caudal length 9.4 8.8?11.1 (N = 4) 10.1 10.1 9.0?14.3 (N = 8) 10.5 6.5 5.3
Per cent of head length
Anus to anal-fin insertion 8.7 6.8?15.0 (N = 6) 9.6 14.8 7.5?15.4 (N = 10) 11.2 12.3 9.8
Pectoral-fin length 37.0 33.9?42.2 (N = 7) 38.3 30.1 27.0?35.3 (N = 10) 31.3 47.8 49.1
Head depth at eye 24.6 28.1?33.3 (N = 6) 30.3 ? 24.3?26.4 (N = 3) 25.4 34.5 34.0
Head depth at nape 48.3 44.5?60.3 (N = 6) 49.7 42.3 39.1?45.2 (N = 10) 41.9 53.5 55.7
Head width 21.2 21.5?26.4 (N = 6) 23.3 ? 17.3?22.1 (N = 3) 19.4 24.0 24.0
Snout length 61.3 58.7?63.9 (N = 6) 62.2 65.8 60.1?65.1 (N = 10) 63.4 63.7 65.3
Posterior naris to snout 8.8 7.0?10.0 (N = 6) 8.6 4.3 4.6?5.6 (N = 10) 4.9 7.3 7.0
Posterior naris to eye 50.3 46.6?55.3 (N = 6) 52.7 56.5 49.0?55.9 (N = 10) 53.5 54.4 54.6
Mouth length 6.6 5.2?6.8 (N = 6) 6.1 5.8 5.4?6.4 (N = 10) 6.0 5.2 4.3
Internarial distance 3.5 2.5?3.5 (N = 6) 3.1 3.8 3.2?4.7 (N = 10) 4.0 2.1 2.2
Eye diameter 4.5 3.8?5.6 (N = 6) 4.6 3.6 3.8?4.7 (N = 10) 4.1 4.3 4.0
Interocular width 7.9 7.2?11.6 (N = 6) 9.1 4.7 4.8?6.0 (N = 10) 5.2 5.4 5.3
Postocular distance 40.2 38.8?40.8 (N = 6) 40.1 37.2 36.4?41.0 (N = 10) 38.8 42.3 43.2
Branchial opening 11.6 10.2?14.1 (N = 6) 11.8 9.6 8.6?13.1 (N = 10) 10.6 15.5 18.1
Per cent of caudal length
Tail depth 17.5 15.1?20.7 (N = 4) 18.2 8.7 5.5?11.4 (N = 8) 9.0 21.2 21.7
Caudal-fin length 13.4 18.1?33.0 (N = 4) 24.7 23.9 21.5?33.5 (N = 8) 27.3 36.5 58.2
Number of specimens indicated in parentheses.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 321
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
stripe on body. Mid-dorsal stripe on body very obvious
and extending from rear of head posteriorly to beyond
origin of electroreceptive filament to varying degrees.
Pectoral fin dusky with small, dark chromatophores
overlying fin rays. Anal fin dusky with small, dark
chromatophores overlying fin rays. Caudal fin dark
overall with distal regions hyaline. One small exam-
ined specimen apparently albino.
Distribution: Sternarchorhynchus mendesi is only
known from the R?o San Juan and R?o Guanipa
basins of north-eastern Venezuela, both of which
drain into the Golfo de Paria (Fig. 50).
Secondary sexual dimorphism: No sexual dimorphism
was apparent in the limited sample of S. mendesi.
Etymology: The species name, mendesi, is in honour of
George Nilson Mendes of the Universidade Federal de
Pernambuco, in recognition of his assistance to the
first author during the early phases of his studies of
gymnotiforms.
Material examined
Holotype: ? VENEZUELA. Monagas: Department of
Matur?n, Morichal Largo, R?o Guanipa, 5 km south of
Aguasay (Aguasay at 9?25?N, 63?44?W), Golfo de
Paria drainage, collected by D. C. Taphorn, L. Page
et al., 2.vii.1998; MCNG 29129, (155).
Paratypes: ? VENEZUELA. Monagas: Department of
Matur?n, Morichal Largo, R?o Guanipa, 5 km south of
Aguasay (Aguasay at 9?25?N, 63?44?W), Golfo de
Paria drainage, collected by D. C. Taphorn, L. Page
et al., with holotype, 2.vii.1998; MCNG 55850, 1 (118
CS; formerly MCNG 29129, in part). R?o Guanipa,
bridge on Highway 5, Golfo de Paria drainage
(9?22?06?N 63?46?47?W), collected by L. Page et al.,
7.i.1994; INHS 31374, 3 (77.7?157). R?o de Oro, R?os
Guarapiche?San Juan basins, Golfo de Paria drain-
age, L. Page et al., 7.i.1994, INHS 31453, 1 (192).
Department of Matur?n, R?o de Oro, south-west of
Jusep?n (Jusep?n at 9?45?N, 63?31?W), Golfo de Paria
drainage, collected by D. C. Taphorn, L. Page et al.,
2.vii.1998; MCNG 29194, 1 (157). Department of
Matur?n, R?o Aman?, north-west of Santa B?rbara
(Santa B?rbara at 9?37?N, 63?37?W), Golfo de Paria
drainage, collected by D. C. Taphorn, L. Page et al.,
2.vii.1998; MCNG 29166, 1 (104).
STERNARCHORHYNCHUS MESENSIS CAMPOS-dA-PAZ
(FIGS 57, 58; TABLE 10)
Sternarchorhynchus mesensis Campos-da-Paz, 2000:
531, figs 5, 6 [type locality: Brazil, Goi?s, R?o
Tocantins (upper R?o Tocantins region), at Serra de
Mesa dam, munic?pios Mina?u/Urua?u (?Mina?u/
Cavalcante?), approximately 13?50?S, 18?19?W]. ?
Albert, 2003: 501 [in listing of members of genus]. ?
Triques, 2007: 125 [Brazil, Rio Tocantins basin].
Diagnosis: Sternarchorhynchus mesensis is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the first and second branchiostegal rays of
approximately the same size, the presence of a defi-
nite series of scales along the mid-dorsal region of the
body, the hyaline anal fin, the lateral line extending
posteriorly to the base of the caudal fin, the posses-
sion of five branchiostegal rays, 11?14 premaxillary
teeth, two rows of teeth on the dentary with ten to 11
teeth in the outer row, 171?189 total anal-fin rays,
13?18 anterior unbranched anal-fin rays, 16?17 pre-
caudal vertebrae, 11?13 scales above the lateral line
at the midbody, the greatest body depth (10.0?12.3%
of LEA), the preanal distance (14.2?17.0% of LEA),
the prepectoral-fin distance (21.4?23.8% of LEA), the
caudal length (9.0?14.3% of LEA), the distance from
the anus to the insertion of the anal fin (7.5?15.4% of
HL), the caudal length (9.0?14.3% of LEA), the head
length (20.5?23.6% of LEA), the distance from the
posterior nares to the eye (49.0?56.5% of HL), the eye
diameter (3.6?4.7% of HL), the height of the branchial
opening (8.6?13.1% of LEA), the head depth at the
nape (39.1?45.2% of HL), the interocular distance
(4.7?6.0% of HL), the distance from the posterior
naris to the snout (4.3?5.6% of HL), the postocular
length (36.4?41.0% of HL), the length of the pectoral
fin (27.0?35.3% of HL), and the tail depth (5.5?11.4%
of caudal length).
Figure 57. Sternarchorhynchus mesensis, paratype, 127 mm total length, MNRJ 11613; Brazil, upper Rio Tocantins,
munic?pios de Mina?u and Urua?u, at Serra de Mesa dam.
322 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Description: Morphometric data for examined speci-
mens in Table 10.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
curved ventrally. Mouth terminal with fleshy process
at anterior limit of dentary. Rictus located along ver-
tical slightly anterior of anterior naris. Anus and
urogenital papilla located ventral to head, with posi-
tion ontogenetically variable. Structures located
approximately at vertical one orbital diameter poste-
rior of eye in small specimens, and within area delim-
ited posteriorly by vertical running through eye and
anteriorly by vertical approximately one orbital diam-
eter anterior of eye in larger specimens. Combined
opening for anus and urogenital papilla longitudi-
nally ovoid.
Premaxilla with 11?14 teeth (N = 5) apparent in
whole specimens and nine to ten teeth (N = 3) in
cleared and stained material. Dentary with two tooth
rows; outer row with eight teeth and inner row with
three teeth (N = 5).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16?17 (13?14 ante-
rior; three transitional; N = 5).
Pectoral-fin rays ii + 12?13 [ii + 13] (N = 9). Anal-fin
origin located anterior to opercle. Anterior
unbranched anal-fin rays 23?28 (N = 10). Total anal-
fin rays 171?189 [181] (N = 8). Scales above lateral
line at midbody 11?13 [13] (N = 10). Scales present
along mid-dorsal region to origin of electroreceptive
filament. Origin of midsaggital electroreceptive fila-
ment located on posterior half of body, approximately
at 60% of TL. Filament extending posteriorly to ver-
tical through posterior terminus of base of anal fin.
Tail compressed and short, ending in small, caudal
fin. Caudal-fin rays 13?15 [14] (N = 8).
Coloration in alcohol: Overall ground coloration
ranging from light tan to brown with pigmentation
darker on dorsal portions of head and body. Snout and
remainder of head with narrow, lightly coloured stripe
extending to rear of head. Stripe extending in some
individuals onto mid-dorsal region. Stripe on head
and anterior portion of body indistinct in some speci-
mens. Anal, caudal, and pectoral fins hyaline overall,
but with some dark chromatophores along margins of
rays, but lacking distinct bands of dark pigmentation
along distal margins of fins.
Distribution: Sternarchorhynchus mesensis is known
from sites in the upper Rio Tocantins system (Fig. 58)
and has been collected in caves of the S?o Domingos
karst region (see Ecology below).
Figure 58. Map of central and northern South America showing geographical distribution of Sternarchorhynchus
mesensis, Sternarchorhynchus montanus sp. nov. (1 = holotype locality), and Sternarchorhynchus mormyrus (some
symbols represent more than one locality and/or lot of specimens).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 323
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Ecology: Several examined lots of S. mesensis origi-
nated in caves within the S?o Domingos karst region
in the upper portions of the Rio Tocantins basin. The
region is home to numerous epigean fishes (Bichuette
& Trajano, 2003, 2004), some of which are limited to
the cave systems whereas some others occur in both
subterranean and surface drainages. Sternarchorhyn-
chus mesensis demonstrates the latter pattern, occur-
ring in both settings, with several population samples
originating in caves (MZUSP 88577, MZUSP 24993,
MZUSP 62652, MZUSP 44116) and others (MZUSP
58623, MZUSP 24497) from surface waters in the
vicinity of those caves. Sternarchorhynchus mesensis
appears to be well adapted to epigean habitats as
indicated by the overall condition and sexual matu-
rity of the individuals from cave habitats. Given the
continuity between surface and epigean waters in the
S?o Domingos region (Bichuette & Trajano, 2004), it
is impossible to determine whether the cave popula-
tions live their entire life cycles and reproduce in that
epigean settings.
Secondary sexual dimorphism: No sexual dimorphism
was reported for the species by Campos-da-Paz (2000)
or is apparent in examined specimens.
Remarks: The samples of S. mesensis from epigean
and surface locations around S?o Domingos differ
somewhat from those from the main river channels of
the Rio Tocantins. Variation in the available samples
does not unequivocally separate the S?o Domingos
samples from individuals of S. mesensis from the type
region. Samples from intervening regions are neces-
sary to resolve the question of whether these differ-
ences represent geographical variation or a possible
second form.
Sternarchorhynchus mesensis was collected at the
same locality as the type series of S. axelrodi. The two
species differ in various details of pigmentation along
with the meristic and morphometric features detailed
under Remarks for S. axelrodi.
Material examined
BRAZIL. Goi?s: Rio Tocantins, upper Rio Tocantins
region, munic?pios Mina?u and Urua?u, at Serra da
Mesa dam (approximately 13?50?S, 48?19?W); MNRJ
11611, 2 of 4 (cleared and stained paratypes), MNRJ
11613, 4 of 7 (115?127, paratypes); MZUSP 57497, 1
(170). Serra da Mesa, Munic?pio de Mina?u. MZUSP
58623, 1 (220), re-emergence of Rio Ang?lica/Bezerra,
Parque Estadual da Terra Ronca, S?o Domingos;
MZUSP 54100, 1 (180). Lagos of Ribeir?o do Bezerra,
S?o Domingos; MZUSP 24497, 2 (145?212). Rio
Ang?lica, Caverna Ang?lica, near its point of
re-emergence, below cachoeira; MZUSP 88577, 1 (81).
Rio S?o Mateus, Gruta Matilde, Munic?pio de S?o
Domingos; MZUSP 24993, 1 (170). Caverna S?o
Mateus, Imbira, Matilde II; MZUSP 62652, 1 (143).
Rio S?o Mateus, Gruta S?o Mateus, Imbira, S?o Dom-
ingos; MZUSP 44116, 1 (188).
STERNARCHORHYNCHUS MONTANUS SP. NOV.
(FIGS 58, 59; TABLE 10)
Diagnosis: Sternarchorhynchus montanus is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
along the mid-dorsal region of the body, the lateral
line that extends to a point one scale anterior of the
base of the caudal fin, the presence of a more lightly
coloured narrow band of mid-dorsal pigmentation on
the head and mid-dorsal region of the body extending
posteriorly to the origin of the electroreceptive fila-
ment and sometimes beyond that point, the distinctly
dusky anal fin without a dark basal band, the pos-
session of six to seven teeth on the premaxilla, six to
seven teeth in the outer row of the dentary, 23?31
anterior unbranched anal-fin rays, 187?191 total
anal-fin rays, 12?13 pectoral-fin rays, 16 precaudal
vertebrae, the greatest body depth (7.5?13.0% of
LEA), the preanal distance (9.5?10.2% of LEA), the
prepectoral-fin distance (10.9?16.6% of LEA), the
head length (16.3?17.0% of LEA), the distance from
the anus to the anal-fin insertion (9.8?12.3% of HL),
the caudal length (5.3?6.5% of LEA), the head depth
at the eye (34.0?34.5% of HL), the head depth at the
nape (53.5?55.7% of HL), the mouth length (4.3?5.2%
Figure 59. Sternarchorhynchus montanus sp. nov., holotype, male, 226 mm total length, MUSM 31312; Peru,
Amazonas, R?o Mara?on.
324 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
of HL), the snout length (63.7?65.3% of HL), the
distance from the posterior naris to the eye (54.4?
54.6% of HL), the eye diameter (4.0?4.3% of HL), the
internarial distance (2.1?2.2% of HL), the interocular
distance (5.3?5.4% of HL), the postocular distance
(42.3?43.2% of HL), the height of the branchial
opening (15.5?18.1% of HL), the pectoral-fin length
(47.8?49.1% of HL), and the tail depth (21.1?21.7% of
caudal length).
Description: Morphometric data for examined speci-
mens in Table 10.
Lateral line extending posteriorly to point one scale
anterior of base of caudal fin and absent on remainder
of tail and on caudal fin. Snout elongate, compressed
and curved ventrally. Mouth terminal with fleshy
process arising from anterior limit of dentary. Rictus
located along vertical slightly anterior of anterior
naris. Anus and urogenital papilla located ventral to
head, with position of openings variable; located
within area delimited posteriorly by vertical through
eye and anteriorly by vertical approximately four
orbital diameters anterior of eye (secondary sexual
dimorphism). Combined opening for anus and uro-
genital papilla ranging from circular to longitudinally
ovoid.
Premaxilla with six to seven teeth (N = 2) apparent
in whole specimens. Dentary with two tooth rows;
outer row with six to seven teeth and inner row with
two teeth (N = 2).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16 (13 anterior; three
transitional; N = 2).
Pectoral-fin rays ii + 12?13 [12] (N = 2). Anal-fin
origin located anterior to opercle. Anterior
unbranched anal-fin rays 23?31 [23] (N = 2). Total
anal-fin rays 187?191 [187] (N = 2). Scales above
lateral line at midbody nine to 12 [9] (N = 2). Scales
present along mid-dorsal region to origin of electrore-
ceptive filament. Origin of midsaggital electrorecep-
tive filament located approximately at 65% of TL.
Filament extending to point one to two scales anterior
of vertical through posterior terminus of base of anal
fin. Tail compressed and short, ending in small, elon-
gate caudal fin. Caudal-fin rays 12?16 (N = 2).
Coloration in alcohol: Overall coloration of head and
body ranging from tan to dark brown. Snout with
distinct dark band extending from slightly anterior of
eye nearly to tip of snout. Ventrolateral surface of
snout somewhat darker than ground coloration. Two
dark regions on snout together delimit somewhat
lighter intermediate band along lateral surface of
anterior two-thirds of snout. Dorsal margin of dark
pigmentation on snout forms lateral margin of
narrow, lightly coloured stripe running along mid-
dorsal region of snout. More lightly coloured mid-
dorsal stripe continues onto and expands somewhat
laterally on postocular portion of head. Expanded
lightly coloured region slightly less apparent over
posteriormost portion of head, but nonetheless con-
tinuous posteriorly with narrow, mid-dorsal stripe on
body. Mid-dorsal stripe on body obvious, more so in
darker holotype and extending from rear of head
posteriorly to origin of electroreceptive filament or
slightly beyond that point. Pectoral fin dusky, more so
distally; very dark in overall more intensely pig-
mented holotype. Anal fin dusky with small, dark
chromatophores overlying fin rays and inter-radial
filaments. Intensity of pigmentation more pronounced
along distal third to half of fin and forming obvious
distal dark band. Caudal fin dark overall.
Distribution: Sternarchorhynchus montanus is known
from two locations in the R?o Mara?on of Peru
(Fig. 58). It is uncertain where the two nontype speci-
mens originated because they were secured from a
dealer in the aquarium trade based in Iquitos, north-
eastern Peru. If the locality information associated
with the nontypes is correct, it would extend the
distribution of S. montanus to the Iquitos region. The
two nontypes agree with the type series in all features
that can be unequivocally determined, but both have
regenerated tails, which makes it impossible to count
the total number of anal-fin rays or determine mor-
phometric values dependent on measurements taken
to the end of the anal fin.
Secondary sexual dimorphism: Sternarchorhynchus
montanus does not demonstrate the sexual dimor-
phism of the dentary and associated dentition present
in some congeners. The male holotype is distinctly
darker overall than the female paratype. A similar
difference in coloration occurs between the nontype
male and female. The female nontype, which is larger
than the paratypic female, also has the posterior
portion of the snout deeper than in the males. This
specimen has the combined opening for the anus and
urogenital papilla positioned approximately four
orbital diameters anterior of the vertical through the
eye contrary to the location of those combined open-
ings approximately at the vertical through the eye in
the nontype male of similar size and the male holo-
type and female paratype, both of which are of
smaller sizes. This may indicate both ontogenetic and
sexual dimorphism in the location of that opening
comparable to that in congeners.
Etymology: The species name, montanus, from the
Latin for mountains, refers to the type location of the
type series in the foothills of the Andean Cordilleras.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 325
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Material examined
Holotype: ? PERU. Amazonas: R?o Mara?on, pongo
above Borja, 35.5 km north-east Juan Velasco, Santa
Maria de Nieva (4?27?36?S, 77?34?53?W), collected by
N. K. Lujan, D. C. Werneke, D. C. Taphorn, A. S.
Flecker, K. A. Capps, D. P. German, D. Osorio,
6.viii.2006; MUSM 31312 (226; formerly AUM 46270,
in part).
Paratype: ? PERU. Amazonas: R?o Mara?on, vicinity
of Santa Maria de Nieva (Santa Maria de Nieva at
4?27?36?S, 77?34?53?W), collected by D. J. Stewart,
16.iv.1980; LACM 41741?44, 1 (258, female).
Nontype specimens: ? PERU. Amazonas: R?o Amazo-
nas, near Iquitos, 1 h above or below, purchased from
aquarium fish dealer at Belen, 20.i.2004; UF uncata-
logued, 2 (276?277, male and female).
STERNARCHORHYNCHUS MORMYRUS (STEINDACHNER)
(FIGS 58, 60, 61; TABLE 11)
Sternarchus mormyrus Steindachner, 1868a: 176
[description of species in abstract of primary descrip-
tion that appeared in Steindachner, 1868b]. Stein-
dachner, 1868b: 253, pl. 1, fig. 3 [more detailed
description following from Steindachner, 1868a; type
locality reported as Brazil, Marabitanos (= R?o Negro,
north of Marabitanas at foot of Cocui mountains;
Remarks); head and anterior portion of body of type
illustrated]. ? Eigenmann & Eigenmann, 1891: 62
[assignment to Sternarchorhynchus]. ? Ellis, 1913:
141 [placed as junior synonym of S. oxyrhynchus]. ?
Fern?ndez-Y?pez, 1967: 18 [species resurrected from
synonymy of S. oxyrhynchus]. ? Eschmeyer, 1998:
1122 [discussion as to which publication constitutes
original description of species]. Sternarchorhynchus
oxyrhynchus, Fowler, 1951: 431 [in part; citations of
Sternarchus mormyrus and S. mormyrus, not other
references].
Sternarchorhynchus mormyrus, Mago-Leccia, 1970:
76 [Venezuela]. ? Machado-Allison, 1987: 132 [llanos
of Venezuela]. ? Mago-Leccia, 1994: 37, fig. 54 [as
valid species in listing of members of genus]. ?
Taphorn et al., 1997: 80 [Venezuela]. ? Campos-da-
Paz, 2000: 528, fig. 2 [as valid species of Sternarcho-
rhynchus in key to species of genus; syntype
illustrated]. ? Albert, 2003: 501 [in listing of members
of genus]. ? Lasso et al., 2004b: 142 [R?o Orinoco
basin in Colombia and Venezuela]. ? Lasso et al.,
2004a: 181 [Venezuela; R?o Orinoco basin]. ? Cramp-
ton, 2007: 289 [widespread in Amazon and Orinoco
basins]. ? Triques, 2007: 125 [Amazon basin].
Diagnosis: Sternarchorhynchus mormyrus is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the absence of scales along the mid-dorsal
region of the body as far posteriorly as the origin of
the electroreceptive filament, and the possession of
222?245 anal-fin rays.
Description: Morphometric data for examined speci-
mens in Table 11.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
curved ventrally. Mature males with wider snout than
females (de Santana & Crampton, 2006: 58). Mouth
terminal and relatively small, with rictus located
anterior to vertical through posterior naris. Anus and
urogenital papilla located ventral to head, with posi-
tion ontogenetically variable. Smaller examined
specimens (c. 190 mm TL) with both structures posi-
tioned along vertical midway between rear of eye and
Figure 60. Sternarchorhynchus mormyrus, illustration of
head of one of the syntypes (from Steindachner, 1868b:
table 1, fig. 3). Figure reversed from original orientation.
Figure 61. Sternarchorhynchus mormyrus, male, 315 mm total length, USNM 375479; Brazil, Amazonas, Rio Amazonas.
326 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
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rn
ar
ch
or
h
yn
ch
u
s
m
or
m
yr
u
s,
S
te
rn
ar
ch
or
h
yn
ch
u
s
ox
yr
h
yn
ch
u
s,
an
d
S
te
rn
ar
ch
or
h
yn
ch
u
s
re
tz
er
i
S
.
m
or
m
yr
u
s
S
.
ox
yr
h
yn
ch
u
s
S
.
re
tz
er
i
R
an
ge
M
ea
n
H
R
an
ge
M
ea
n
H
P
ar
at
yp
es
M
ea
n
To
ta
l
le
n
gt
h
(m
m
)
11
9?
31
5
(N
=
15
)
?
46
9
20
7?
34
8.
3
(N
=
22
)
?
37
2
28
1?
26
4
(N
=
5)
?
L
en
gt
h
to
en
d
of
an
al
fi
n
(m
m
)
23
6?
25
5
(N
=
2)
?
38
8
27
9?
19
3
(N
=
22
)
?
34
2
22
6?
26
9
(N
=
4)
?
H
ea
d
le
n
gt
h
(m
m
)
27
.0
?6
7.
6
(N
=
15
)
?
57
.0
35
.8
?4
7.
8
(N
=
21
)
?
67
.8
52
.3
?6
8.
0
(N
=
6)
?
C
au
da
l
le
n
gt
h
(m
m
)
14
.1
?1
5.
3
(N
=
2)
?
81
.0
25
.4
?6
9.
3
(N
=
18
)
?
24
.6
25
.2
?3
0.
1
(N
=
2)
?
P
er
ce
n
t
of
le
n
gt
h
to
en
d
of
an
al
fi
n
A
n
al
-fi
n
ba
se
81
.7
?8
4.
3
(N
=
2)
83
.0
87
.8
82
.2
?9
3.
3
(N
=
22
)
86
.0
85
.6
84
.2
?8
6.
9
(N
=
5)
85
.4
D
is
ta
n
ce
sn
ou
t
to
an
u
s
14
.1
?1
4.
2
(N
=
2)
14
.1
?
10
.1
?1
5.
2
(N
=
21
)
13
.8
3.
7
9.
8?
12
.8
(N
=
8)
11
.6
P
re
an
al
-fi
n
di
st
an
ce
15
.5
?1
6.
2
(N
=
2)
15
.9
12
.5
13
.7
?1
9.
3
(N
=
21
)
16
.1
13
.5
13
.0
?1
5.
2
(N
=
6)
13
.8
P
re
pe
ct
or
al
-fi
n
di
st
an
ce
21
.0
?2
1.
4
(N
=
2)
21
.2
15
.3
16
.7
?2
0.
4
(N
=
22
)
18
.6
19
.8
18
.5
?2
1.
3
(N
=
5)
19
.6
G
re
at
es
t
bo
dy
de
pt
h
11
.7
?1
2.
1
(N
=
2)
11
.9
9.
4
6.
3?
8.
2
(N
=
22
)
7.
4
8.
3
8.
7?
10
.1
(N
=
5)
9.
2
H
ea
d
le
n
gt
h
21
.3
?2
1.
8
(N
=
2)
21
.5
14
.6
17
.0
?2
3.
2
(N
=
21
)
19
.0
19
.8
18
.5
?2
0.
2
(N
=
5)
19
.4
C
au
da
l
le
n
gt
h
6.
0
(N
=
2)
6.
0
20
.8
14
.4
?3
1.
2
(N
=
20
)
23
.9
7.
1
9.
2?
10
.3
(N
=
2)
9.
7
P
er
ce
n
t
of
h
ea
d
le
n
gt
h
A
n
u
s
to
an
al
-fi
n
in
se
rt
io
n
5.
2?
16
.1
(N
=
15
)
10
.3
?
6.
1?
19
.9
(N
=
21
)
10
.8
25
.8
5.
7?
14
.8
(N
=
6)
17
.7
?2
5.
6
(N
=
3)
11
.1
22
.0
P
ec
to
ra
l-
fi
n
le
n
gt
h
37
.5
?4
7.
4
(N
=
15
)
41
.7
38
.0
27
.0
?3
7.
7
(N
=
21
)
34
.7
35
.4
34
.4
?3
9.
1
(N
=
9)
36
.5
H
ea
d
de
pt
h
at
ey
e
24
.9
?3
0.
8
(N
=
15
)
27
.7
24
.9
18
.3
?2
3.
1
(N
=
21
)
21
.5
25
.0
21
.4
?2
7.
7
(N
=
9)
24
.7
H
ea
d
de
pt
h
at
n
ap
e
43
.6
?5
4.
3
(N
=
15
)
48
.0
?
26
.8
?3
7.
7
(N
=
21
)
34
.2
34
.7
34
.1
?4
1.
8
(N
=
9)
37
.2
H
ea
d
w
id
th
21
.0
?2
9.
4
(N
=
15
)
24
.8
16
.6
13
.7
?2
1.
5
(N
=
21
)
18
.0
15
.9
16
.4
?1
8.
7
(N
=
9)
17
.6
S
n
ou
t
le
n
gt
h
52
.9
?6
3.
3
(N
=
15
)
55
.6
65
.7
49
.5
?6
5.
7
(N
=
21
)
62
.7
68
.4
65
.4
?7
1.
2
(N
=
9)
68
.0
P
os
te
ri
or
n
ar
is
to
sn
ou
t
8.
0?
10
.6
(N
=
15
)
9.
3
7.
0
4.
8?
6.
8
(N
=
21
)
5.
8
6.
9
5.
7?
7.
0
(N
=
9)
6.
3
P
os
te
ri
or
n
ar
is
to
ey
e
39
.7
?4
7.
4
(N
=
15
)
44
.9
58
.7
45
.4
?5
8.
4
(N
=
21
)
55
.1
61
.7
57
.3
?7
4.
0
(N
=
9)
61
.9
M
ou
th
le
n
gt
h
6.
1?
9.
8
(N
=
15
)
8.
1
8.
5
6.
0?
11
.0
( N
=
20
)
7.
9
6.
0
4.
2?
6.
6
(N
=
9)
5.
1
In
te
rn
ar
ia
l
di
st
an
ce
3.
4?
4.
8
(N
=
15
)
4.
1
3.
5
0.
9?
4.
1
(N
=
20
)
2.
8
3.
3
2.
2?
3.
4
(N
=
9)
2.
9
E
ye
di
am
et
er
3.
2?
6.
3
(N
=
15
)
4.
1
4.
0
3.
2?
5.
7
(N
=
21
)
4.
3
2.
8
2.
5?
3.
4
(N
=
9)
2.
8
In
te
ro
cu
la
r
w
id
th
4.
2?
9.
9
(N
=
15
)
6.
0
5.
6
4.
6?
7.
6
(N
=
21
)
6.
1
4.
6
3.
9?
6.
4
(N
=
9)
4.
8
P
os
to
cu
la
r
di
st
an
ce
27
.7
?4
8.
5
(N
=
15
)
45
.9
20
.1
26
.0
?3
6.
8
(N
=
21
)
34
.3
31
.9
31
.6
?3
4.
9
(N
=
9)
33
.5
B
ra
n
ch
ia
l
op
en
in
g
10
.7
?1
6.
2
(N
=
12
)
13
.6
6.
2
8.
3?
14
.5
(N
=
21
)
11
.3
11
.3
10
.0
?1
2.
5
(N
=
9)
11
.4
P
er
ce
n
t
of
ca
u
da
l
le
n
gt
h
T
ai
l
de
pt
h
29
.7
?3
1.
8
(N
=
2)
30
.7
4.
9
3.
7?
14
.2
(N
=
20
)
7.
3
21
.4
15
.3
?2
1.
4
(N
=
2)
17
.5
C
au
da
l-
fi
n
le
n
gt
h
42
.4
?6
4.
9
(N
=
2)
53
.6
?
6.
15
?3
4.
9
(N
=
18
)
14
.7
27
.7
21
.8
?2
7.
7
(N
=
2)
24
.1
N
u
m
be
r
of
sp
ec
im
en
s
in
di
ca
te
d
in
pa
re
n
th
es
es
.
H
,
h
ol
ot
yp
e;
ra
n
ge
in
cl
u
de
s
n
on
ty
pe
sp
ec
im
en
s.
M
an
y
sp
ec
im
en
s
of
S
.m
or
m
yr
u
s
th
at
se
rv
ed
as
ba
si
s
fo
r
m
ea
su
re
m
en
ts
h
ad
ta
il
s
da
m
ag
ed
as
a
co
n
se
qu
en
ce
of
ap
pa
re
n
t
pr
ed
at
io
n
an
d
va
ri
ou
s
pr
op
or
ti
on
s
co
u
ld
n
ot
be
de
te
rm
in
ed
fo
r
th
es
e
in
di
vi
du
al
s.
S
ex
u
al
ly
di
m
or
ph
ic
fe
at
u
re
s
fo
r
S
.
re
tz
er
i
ar
e
pr
es
en
te
d
as
tw
o
en
tr
ie
s.
F
ir
st
en
tr
y
is
da
ta
fo
r
al
l
sp
ec
im
en
s
ot
h
er
th
an
se
xu
al
ly
di
m
or
ph
ic
m
at
u
re
m
al
es
w
it
h
in
fo
rm
at
io
n
fo
r
se
xu
al
ly
di
m
or
ph
ic
m
al
e
in
se
co
n
d
en
tr
y
ba
se
d
on
th
re
e
sp
ec
im
en
s
of
37
1?
39
0
m
m
to
ta
l
le
n
gt
h
.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 327
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
posterior border of opercle. Midsized specimens (c.
315 mm TL) with anus and urogenital papilla located
along vertical one-third of distance between posterior
margin of eye and posterior border of opercle. Largest
examined specimens (c. 450?470 mm SL) with open-
ings shifted distinctly anteriorly and positioned along
verticals falling within region delimited posteriorly by
vertical located slightly anterior to eye and anteriorly
by vertical approximately one-third of distance
between anterior margin of eye and tip of snout.
Combined opening for anus and urogenital papillae
circular to longitudinally ovoid in females, longitudi-
nally ovoid in males.
Premaxilla with ten to 11 [ten in both syntypes]
teeth and ten replacement teeth in cleared and
stained specimen (122 TL) and with ten to 14 func-
tional teeth apparent in whole specimens (N = 5).
Sexual dimorphism in form of dentary and associated
dentition present in some congeners not apparent in
examined specimens. Dentary in cleared and stained
specimen (122 TL) with one functional tooth row of
nine curved conical teeth bordered medially by eight
replacement teeth. Whole specimens with two tooth
rows with 11?16 [13 in both syntypes] teeth in outer
row and three to four [four in one syntype] teeth
apparent in inner row (N = 4).
Branchiostegal rays five; with first ray narrow
and elongate, second and third rays somewhat
wider, and fourth and fifth rays very large and
broad with triangular ventral margins. Precaudal
vertebrae 17?18 (four anterior; three to four transi-
tional; N = 23).
Pectoral-fin rays ii + 13?15 (N = 23) [13 and 14
branched rays in syntypes]. Anal-fin origin located
anterior to opercle. Anterior unbranched anal-fin rays
22?38 (N = 14). Total anal-fin rays 222?245 (N = 15)
[226 in syntypes according to Steindachner (1868b:
254) but with 228 rays in smaller and 225 in larger
syntypes; both specimens with regenerated tails].
Scales above lateral line at midbody nine to 12 [11
scales in syntypes] (N = 20). Scales along mid-dorsal
line absent in many specimens along most of body
anterior to origin of midsaggital electroreceptive fila-
ment. Larger specimens with areas lacking scales
sometimes separated by scaled mid-dorsal patches,
and with position and extent of unscaled regions
variable both ontogenetically and within some popu-
lation samples. Origin of midsaggital electroreceptive
filament located approximately at 60% of TL.
Filament extending posteriorly beyond vertical
through posterior terminus of base of anal fin for
distance of approximately four scales. Tail com-
pressed and short, ending in small, elongate, pointed
caudal fin. Caudal-fin rays 16?19 (N = 6) [16?17 in
syntypes according to Steindachner (1868b: 254) but
fins regenerated in both specimens].
Coloration in alcohol: Overall ground coloration light
brown. Head in smaller specimens with scattered,
small, dark chromatophores dorsally and on lateral
surface of postocular region. More concentrated band
of dark chromatophores located along dorsal region of
snout in region from vertical through posterior naris
to slightly posterior of eye. Dark pigmentation on
head more obvious in larger individuals, with dark
dorsal preorbital region often more obvious and some-
times extending anteriorly nearly to snout tip. Body
in small specimens with light brown pigmentation
overlain by relatively dense pattern of irregularly
positioned, small, dark chromatophores. Larger indi-
viduals with overall coloration distinctly darker, but
without any distinct pigmentation pattern.
Pectoral fin in smaller specimens hyaline to very
slightly dusky distally. Distal pigmentation on fin
increasingly pronounced in both extent and intensity
ontogenetically. Largest individuals with pectoral fin
sometimes nearly completely very darkly pigmented
and with overall pigmentation distinctly darker than
that present in juveniles. Anal fin in smallest exam-
ined individuals hyaline to very slightly pigmented
distally, with distal pigmentation distinctly darker in
largest specimens and sometimes covering distal two-
thirds of fin and forming irregular band. Caudal fin
unpigmented.
Distribution: Sternarchorhynchus mormyrus is known
from the mainstream of the Amazon River from
Manaus in the central portions of the basin to the
vicinity of Iquitos in north-eastern Peru, the R?o
Negro, and from the R?o Orinoco basin in both Ven-
ezuela and south-eastern Colombia (Fig. 58). A pho-
tograph that we examined shows a specimen that
either S. mormyrus or a very similar undescribed
species captured in the central portions of the Rio
Madeira in the vicinity of Porto Velho. This location
lies a considerable distance from the mainstream
Amazon. Two questionable records of the species (see
comments under Remarks below) would extend its
distribution to the lower portions of the Amazon River
basin.
The distribution of this species is the greatest in
Sternarchorhynchus, but we did not identify any dif-
ferences across that range (e.g. Orinoco versus
Amazon basins) that justified the recognition of more
than one species. Comparable broad ranges occur in
some fish species that have been critically analysed
across those basins within the Apteronotidae (e.g.
Sternarchorhamphus muelleri, Campos-da-Paz, 1995:
fig. 2) and other major groups in those ichthyofaunas
(e.g. Siluriformes: Hoplosternum littorale, Reis, 1997:
fig. 4; Cetopsis coecutiens, Vari, Ferraris & de Pinna,
2005: fig. 19. Cichlidae: Cichla ocellaris, Cichla
328 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
temensis, Kullander & Ferreira, 2007: figs 9, 75.
Characidae: Roeboides affinis, de Lucena, 2007: fig. 3).
Ecology: Juveniles of S. mormyrus live within v?rzea
along the shores of the main river (C. D. de Santana,
pers. observ.) whereas adults are inhabitants of main
river channels (Cox-Fernandes, Podos & Lundberg,
2004: supplemental information).
Electrical organ discharge: Crampton & Albert (2006:
688) briefly described the EOD in S. mormyrus as
resembling the IR Type B pattern, but ?in which the
descending voltage curve has no, or only a very slight,
outward inflection giving the waveform an asym-
metrical aspect in the horizontal plane?. These
authors consequently termed this EOD pattern as
type C.
Secondary sexual dimorphism: de Santana & Cramp-
ton (2006: 58) remarked that S. mormyrus demon-
strates sexual dimorphism in the form of the anterior
portion of the neurocranium, with mature males
having a wider snout than do conspecific females.
Hilton & Cox-Fernandes (2006: 836) reported that S.
mormyrus demonstrates sexual dimorphism of the
lower jaw, with males having distended jaws relative
to females. These authors also reported that males
have many more teeth on that jaw than do females.
We have not found such differences in the form of the
lower jaw and dentary dentition in the material of S.
mormyrus examined in this study.
Remarks: The two extant known syntypes of Sterna-
rchus mormyrus (NMW 65336, 65345; Eschmeyer,
1998: 1122), both have regenerated tails makes it
impossible to determine the total length and other
distances and proportions that are a function of that
measurement. The count of the anal-fin rays is also
likely to be reduced as a consequence of that damage.
Steindachner (1868b: 253) reported the type locality
of Sternarchus mormyrus as ?Maribitanos? without
elaboration as to the river basin and country within
which the collecting site was located. That site is
undoubtedly Marabitanas, the type locality for
various other lots of fishes deposited at NMW (e.g.
Heros psittacus Heckel) collected at ?Rio-negro, nor-
dlich von Marabitanas am Fusse des Berges Cocui?
(= R?o Negro, north of Marabitanas at foot of Cocui
mountains; Kullander, 2003: 637). Marabitanas is at
approximately 00?58?N, 66?51?W in the region where
Colombia, Brazil, and Venezuela border each other
along the upper R?o Negro.
Steindachner often published two accounts of
species that he described as new. One paper was
typically a brief abstract in the Anzeiger de Akademie
der Wissenschaften, Wien with the name of the species
and a brief listing of certain diagnostic characters. He
complimented these brief initial accounts with a
second more detailed account that was often accom-
panied by detailed illustrations. These accounts
were typically published in the Sitzungsberichte
der Akademie der Wissenschaften, Matematicsh-
Naturwissenschafrliche Classe, Wien, although on
occasion in other outlets. In the case of Sternarchus
mormyrus, the Sternarchorhynchus mormyrus of this
study, previous authors (e.g. Mago-Leccia, 1994;
Campos-da-Paz, 2000) understandably assumed that
the detailed description with an associated illustra-
tion of the head and anterior portion of the body of a
syntype (Steindachner, 1868b) constituted the formal
description. In this instance the abstract (Stein-
dachner, 1868a) was published first (Eschmeyer,
1998: 1122) and, thus, constitutes the formal original
description of Sternarchus mormyrus.
Eigenmann & Bean (1907) proposed that S. curvi-
rostris was a likely senior synonym of S. mormyrus.
Sternarchorhynchus mormyrus and S. curvirostris
were, in turn, placed as junior synonyms of S. oxy-
rhynchus by Ellis (1913: 141), who considered the
latter species to be a monotypic, morphologically
highly variable form. Fern?ndez-Y?pez (1967: 18) res-
urrected S. mormyrus and S. curvirostris from syn-
onymy on the basis of various external features of
the head. Based on the illustration provided by
Fern?ndez-Y?pez (1967: 19), the material that he
reported as S. curvirostris differed from that species
in various details and is likely to be another species.
It is also questionable whether Fern?ndez-Y?pez had
material of S. mormyrus at hand given the differences
between the illustrated specimen and S. mormyrus,
most notably in the form of the snout and position
of the anus and urogenital papilla. That question
notwithstanding, the practice of recognizing S.
mormyrus as a distinct species was continued by
Mago-Leccia (1994: 37) and Campos-da-Paz (2000:
528). Our results confirm the distinctiveness of S.
mormyrus. Indeed it is one of the more easily recog-
nized species within Sternarchorhynchus.
Eigenmann & Bean (1907: 666) reported on speci-
mens of what they identified as S. mormyrus from
along the Amazon River in the region between
Manaus and Par? (= Bel?m). Although S. mormyrus
does occur in that region, those specimens had 191 to
194 anal-fin rays, a range distinctly lower than the
222 to 245 rays present in S. mormyrus. Examination
of the specimens (USNM 52542) that served as the
basis for that record has shown them to be S. starksi.
The easternmost records for S. mormyrus within
the Amazon basin in this study (Fig. 58) are based on
two specimens (USNM 373026, USNM 373050)
lacking portions of their tails. This damage renders a
definitive identification problematic, but these speci-
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 329
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
mens are assigned to S. mormyrus based on their
correspondence to that species in other features
including morphometrics of the head, overall head
and body form, and coloration.
Material examined
BRAZIL. Amazonas: Marabitanas (approximately
00?58?N, 66?51?W), NMW 65345, approximately 315
[syntype of Sternarchus mormyrus, tail regenerated];
NMW 65336, 384 [syntype of Sternarchus mormyrus,
tail regenerated]. Rio Solim?es, Ilha do Careiro, Lago
Juanico; INPA 4899, 2 (378?413), INPA 27473, 3
(243?251), INPA 27474, 1 (214); INPA 4900, 1 (505).
Rio Solim?es, Ilha da Machantaria, INPA 17608, 1
(342), INPA 17609, 3 (310?350), INPA 27470, 1 (300).
Rio Solim?es, Paran? do Xiborena; INPA 17610, 1
(240), INPA 27475, 1 (270), INPA 27746, 1 (382). Rio
Solim?es, Paran? do Cuar?; INPA 17611, 1 (180). Rio
Japur?, mouth of Lago Caxinguba; INPA 18295, 1
(243). Rio Purus, Beruri; INPA 27477, 1 (365). Lago
Manacapuru (3?06?S, 61?30?W); MCZ 34338, 1 (250).
Rio Amazonas, 28.5 km below Manaus (3?05?33?S,
59?46?27?W); USNM 306843, 2 (1CS, 119?122);
USNM 229916, 1 (133); USNM 375479, 1 (315). Rio
Juta?, near Zinho (2?57?40?S 67?00?48?W); MZUSP
55855, 1 (257). Rio Amazonas, Parintins (2?38?S,
56?46?W); MZUSP 79856, 1 (105). Rio Uaup?s (2?55?S
69?38?W); MZUSP 91647, 1 (410). Rio Negro, 5.4 km
below Unini (1?41?41?S 61?29?19?W); MZUSP 55852, 1
(279). Rio Negro, below Dara? (approximately 0?30?S,
64?40?W); MZUSP 32202, 2, 335?379. Rio Negro, at
Manaus (3?06?S, 60?00?W); MCZ 9347, 1 (258).
COLOMBIA. R?o Orinoco basin, R?o Meta, no speci-
fied locality; IAVHP 2674; 1 (520).
PERU. Amazonas: R?o Mara?on, pongo above
Borja, 35.5 km north-east of Juan Velasco at Santa
Maria de Neiva (approximately 4?50?S, 77?51?W);
AUM 47285, 1 (305; formerly AUM 46270, in part).
Loreto: R?o Amazonas, vicinity of Iquitos, upstream
and downstream of mouth R?o Itaya (3?40?36?S,
73?14?37?W); ANSP 182583, 1 (190).
VENEZUELA. Apure: R?o Guariquito at confluence
with R?o Orinoco; MBUCV 15711, 1 (300). R?o Apure,
in front of mouth of Ca?o Manglar (approximately
7?52?N, 67?36?W); MBUCV 20670, 1 (522). R?o
Matyure, just south of village of Achaguas (7?45?N,
68?15?W); CU 72165, 1 (148). Delta Amacuro: Ca?o at
mouth of Anabata into R?o Orinoco, north of Isla
Portuguesa (approximately 8?37?12?N, 61?47?33?W);
CU 80960, 2 (252?275). R?o Orinoco, south of Isla
Portuguesa, 116 nautical miles (= 214.6 km) upstream
from sea buoy (approximately 8?37?N, 61?49?W);
LACM 43044?5, 1 (420). R?o Orinoco, on north shore
at Isla Portuguesa (approximately 8?37?N, 61?49?W);
LACM 43295?84, 2 (261?273). R?o Orinoco, in front of
Isla Iguana; MBUCV 10512, 1 (200). R?o Orinoco, in
front of Isla Tres Ca?os (8?40?N, 62?00?W; MBUCV
10885, 1 (239), MBUCV 12081, 1 (229). R?o Orinoco,
shallow river downstream from buoy 82, near mouth
of small ca?o (8?28?24?N, 61?17?12?W); USNM
228646, 1 (264). R?o Orinoco (8?40?12?N, 62?00?00?W);
USNM 228875, 1 (495). Gu?rico: Ca?o Casi Seco,
42 km east of Guayabal (8?01?67?N, 67?07?50?W);
MCNG 14427, 1 (110).
The following material is tentatively identified as
S. mormyrus (comments under Remarks above):
BRAZIL. Par?: Rio Amazonas, between Almerim
and Gurup? (01?28?38?S, 52?04?00?W); USNM
373026, 1 (261). Rio Amazonas, 58.5 km below Jurut?,
21.1 km above ?bidos (1?55?56?S, 55?40?58?W);
USNM 373050, 1 (235).
STERNARCHORHYNCHUS OXYRHYNCHUS (M?LLER &
TROSCHEL) (FIGS 62, 63; TABLE 11)
Sternarchus oxyrhynchus M?ller & Troschel, 1848:
640 [type locality: Guyana, Essequibo River; locality
information problematic, Remarks]. ? M?ller &
Figure 62. Sternarchorhynchus oxyrhynchus, male, 348 mm total length, USNM 228788; Venezuela, Delta de Amacuro,
R?o Orinoco.
330 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Troschel, 1849: 16, pl. 2, figs 1, 2 [expanded descrip-
tion of species with accompanying illustration]. ?
G?nther, 1870: 4 [British Guiana; based on original
description]. ? Eigenmann & Eigenmann, 1891: 62
[assignment to Sternarchorhynchus].
Sternarchorhynchus mulleri Castelnau, 1855: 95
[type locality: Guyana, Essequibo River; based on
Sternarchus oxyrhynchus M?ller & Troschel, 1848]. ?
Mago-Leccia, 1994: 36 [as junior synonym of S. oxy-
rhynchus]. ? Campos-da-Paz, 2000: 521 [as junior
objective synonym of S. oxyrhynchus].
Sternarchorhynchus oxyrhynchus, Ellis, 1913: 140,
174 [meristic and morphometric data for holotype
reported; diet; Sternarchus mormyrus and S. curvi-
rostris placed into synonymy of S. oxyrhynchus; not
cited records of species from localities in Guyana]. ?
Fowler, 1951: 431 [in part; not records based on
synonymy of S. mormyrus and S. curvirostris into S.
oxyrhynchus; not cited occurrence in the Amazon
basin and Guianas]. ? Fern?ndez-Y?pez, 1967: 18
[Sternarchus mormyrus and S. curvirostris resur-
rected from synonymy of S. oxyrhynchus]. ? Mago-
Leccia, 1994: 36, fig. 53 [as valid species in listing of
members of genus]. ? Taphorn et al., 1997: 80 [Ven-
ezuela]. ? Albert & Campos-da-Paz, 1998: 423 [phy-
logenetic relationships]. ? Campos-da-Paz, 2000: 528,
fig. 1 [recognized as valid species in key to species of
Sternarchorhynchus; head and anterior portion of
body of holotype illustrated]. ? Albert, 2001: 13 [in
study of phylogenetic relationships]. ? Albert, 2003:
501 [in listing of members of Sternarchorhynchus]. ?
Lasso et al., 2004b: 142 [R?o Orinoco basin in Colom-
bia and Venezuela]. ? Lasso et al., 2004b: 181 [Ven-
ezuela; R?o Orinoco basin]. ? Crampton, 2007: 289
[widespread in Orinoco basin; not cited occurrence in
river systems outside that basin].
Diagnosis: Sternarchorhynchus oxyrhynchus is distin-
guished from all congeners other than S. goeldii by
possessing the following combination of characters:
the gape of the mouth is aligned with main axis of
snout, with the gape elongate and extending posteri-
orly distinctly beyond the vertical through the poste-
rior naris. Sternarchorhynchus oxyrhynchus differs
from S. goeldii in the number of total vertebrae (97?
108 versus 92?94, respectively), the greatest body
depth (6.3?9.2 versus 8.2?10.8 of TL, respectively),
and to a notable degree in head depth at the nape
(26.8?37.7 versus 35.0?44.8 of HL).
Figure 63. Map of central and northern South America showing geographical distribution of Sternarchorhynchus
oxyrhynchus (1 ? Essequibo River, reported type locality of species, but see Remarks in species account concerning possible
erroneous locality information), and Sternarchorhynchus retzeri sp. nov. (2 = holotype locality) (some symbols
represent more than one locality and/or lot of specimens).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 331
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Description: Morphometric data for examined speci-
mens in Table 11.
Lateral line extending posteriorly at least to base of
caudal fin and continuing for short distance onto
basal portions of fin in some specimens. Snout elon-
gate, compressed and very slightly curved ventrally
distally, but with snout having overall anteroventral
orientation. Anus and urogenital papilla located
ventral to head, with position demonstrating little
intraspecific variation and located about two to four
orbital diameters posterior of vertical through poste-
rior margin of eye.
Premaxilla with ten functional teeth and six
replacement teeth in cleared and stained specimen
(N = 1; 280 mm TL). Whole specimens with ten to 13
functional teeth on premaxilla. No obvious sexual
dimorphism present in form of dentary and associ-
ated dentition in examined samples. Dentary with
two rows of teeth along at least anterior portion of
bone. Outer row more elongate, with ten to 12 teeth
in cleared and stained specimens (N = 2; 210?
240 mm TL) and with teeth in region situated short
distance posterior of symphysis shifted somewhat
laterally and pointed slightly dorsolaterally. Outer
tooth row with six associated replacement teeth in
that specimen. Mouth terminal. Gape of mouth
aligned with main axis of snout, elongate and
extending posteriorly distinctly beyond vertical
through posterior naris (Fig. 1A). Lower jaw with
terminal fleshy pad that extends beyond vertical
through anterior limit of snout. Pad orientated
dorsally and overlaps tip of snout in closed
mouth.
Branchiostegal rays five; with first and
second ray narrow and elongate, third to fifth
rays becoming increasingly wider and with fourth
and fifth rays with triangular ventral margins.
Precaudal vertebrae 16?17 (13 anterior; three to
four transitional; N = 12). Total vertebrae 97?108
[108].
Pectoral-fin rays ii + 12?15 [ii + 12] (N = 16). Anal-
fin origin located anterior to vertical through
opercle. Anterior unbranched anal-fin rays 24?26
[23] (N = 7). Total anal-fin rays 212?242 [215]
(N = 12) [215 anal-fin rays reported by M?ller &
Troschel (1848: 640) in original description]. Scales
above lateral line at midbody three to eight [3]
(N = 12). Scales absent along mid-dorsal line from
rear of head to electroreceptive filament origin.
Origin of midsaggital electroreceptive filament
located approximately at 54% of TL. Filament
extending posteriorly beyond vertical through poste-
rior terminus of base of anal fin for distance of
approximately seven scales. Tail compressed and
long, ending in small, elongate, pointed caudal fin.
Caudal-fin rays 15?18 (N = 14).
Coloration in alcohol: Overall ground coloration tan
to light brown. Head and body with small dark chro-
matophores relatively densely scattered over sur-
faces. Dark pigmentation somewhat more developed
dorsally. Some specimens with posteriormost portion
of body and all of tail distinctly darker than remain-
der of body.
Pectoral fin coloration ranging from nearly com-
pletely hyaline to overall darkly pigmented, but with
dark pigmentation most developed distally. Very
lightly pigmented specimens with dark pigmentation
limited to distal most portions of fin. Distal pigmen-
tation on fin increasingly pronounced ontogenetically
in both extent and intensity. Anal fin with variably
developed dark pigmentation distally. Overall more
lightly pigmented specimens often with dark pigmen-
tation limited to posterior half of anal fin and/or
forming narrow band along distal fin margin. Speci-
mens with dark overall coloration with extent of dark
pigmentation increasing both in terms of extension
anteriorly and also in degree to which pigmentation
extends basally from margin of fin. Distal pigmenta-
tion in some darker individuals extending forward
nearly to anteriormost rays of fin and forming irregu-
lar dark band along entire fin margin. Caudal fin
dark even in overall lightly pigmented individuals.
Distribution: Sternarchorhynchus oxyrhynchus is only
known from the R?o Orinoco basin (Fig. 63; see under
Remarks concerning purported occurrence of species
in the Essequibo River, Guyana).
Remarks: Sternarchorhynchus was proposed by
Castelnau (1855) on the basis of a species, S. mulleri,
described in the same publication (this species erro-
neously cited by some authors as S. muelleri or S.
mulleri; Campos-da-Paz, 2000: 521). Mago-Leccia
(1994: 36) noted that S. mulleri was based on S.
oxyrhynchus and as such was a junior synonym of the
latter species. That conclusion was reiterated by
Campos-da-Paz (2000: 521), who specifically pointed
out that S. mulleri was a junior objective synonym of
S. oxyrhynchus under the rules of the International
Code of Zoological Nomenclature.
Sternarchorhynchus oxyrhynchus and S. goeldii
have a distinctive mouth form with the extent of the
gape extending further posteriorly than in all other
congeners and terminating distinctly posterior of the
vertical through the posterior naris. The remaining
species of Sternarchorhynchus have a shorter gape
that fails to extend nearly as far posteriorly. The
mouth form of S. oxyrhynchus was clearly illustrated
by M?ller & Troschel (1849: 16, pl. 2, fig. 2), albeit
without the posterior naris indicated. The 108 total
vertebrae in the type specimen of Sternarchus oxy-
rhynchus (the Sternarchorhynchus oxyrhynchus of
332 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
this study; ZMB 4086) fall at the upper end of the
range for that feature (97?108 vertebrae) amongst the
radiographed specimens of S. oxyrhynchus, but that
count lies distant from the 98?99 vertebrae present in
S. goeldii, the only other species within Sternarcho-
rhynchus characterized by this distinctive elongate
gape.
All specimens examined in the course of this study
that agree with the original description of S. oxyrhyn-
chus and the type specimen of the species in terms of
overall appearance, mouth form, and meristics origi-
nated within the R?o Orinoco basin. In their original
description of Sternarchus oxyrhynchus (the Sternar-
chorhynchus oxyrhynchus of this study), M?ller &
Troschel (1848: 640) reported that the type locality
was the Essequibo River of British Guiana
(= Guyana) with the collector being ?Schomb.?
(= Schomburgk). M?ller & Troschel reiterated that
locality in their more encompassing description of the
species that was accompanied by illustrations (M?ller
& Troschel, 1849: 16, pl. 2, figs 1, 2). None of the
specimens of Sternarchorhynchus that originated in
the Essequibo River basin examined during this
study agree with the original description of S. oxy-
rhynchus. The only species of Sternarchorhynchus we
examined that originated in the Essequibo River
system is S. freemani, a species distinguished from S.
oxyrhynchus in numerous features including the pres-
ence of an unpigmented stripe along the dorsal
midline from the snout to at least the origin of the
electroreceptive filament (versus the lack of such a
stripe in S. oxyrhynchus), the presence of scales along
the mid-dorsal portion of the body to the origin of the
electroreceptive filament (versus the absence of scales
along at least part of that region in S. oxyrhynchus),
and the number of anal-fin rays [170?177 in S. free-
mani versus 212?242 in S. oxyrhynchus, with 215
reported by M?ller & Troschel (1848: 640) in the
original description].
Schomburgk collected in the R?o Orinoco basin in
1838?1839 in association with some of his collecting
efforts in British Guiana (Kullander & Stawikowski,
1997: 113; Riviere, 1998: 2). Given that all examined
samples of S. oxyrhynchus were collected in the
eastern portions of the R?o Orinoco basin, this raises
the possibility that some of the material reported by
M?ller & Troschel (1848: 1849) as having originated
in the Essequibo River might represent specimens
collected in the R?o Orinoco basin with incorrect asso-
ciated locality information.
The original description of Sternarchus oxyrhyn-
chus (M?ller & Troschel, 1848: 640) cited a range of
size of examined specimens (16?18 Zoll) presumably
indicative of least two specimens at hand. The sub-
sequent M?ller & Troschel paper that discussed the
species in greater detail (M?ller & Troschel, 1849:
16) lists, however, only a single length (18 Zoll),
which was indicative of a unique specimen. Eigen-
mann (in Ellis, 1913: 142) similarly reported a
unique ?type? as No. 4086 in the ?Berlin Mus.?
(= ZMB) and only that specimen is now present in
the ZMB holdings (Eschmeyer, 1998; P. Bartsch,
ZMB, pers. comm.). The original description possibly
incorrectly listed a range of sizes despite a unique
type specimen or alternatively a second syntype was
lost subsequent to the original description. Given
the brief timeframe between the two M?ller &
Troschel publications (1848, 1849), the option of an
lapsus in the original description seems the more
likely possibility.
In his study of the Gymnotidae (the Gymnotiformes
of this study), Ellis (1913: 142) considered S. curvi-
rostris and S. mormyrus to be junior synonyms of S.
oxyrhynchus and ascribed the apparent differences
between the nominal species as ?being in part due to
the size of the fish?. The concept of a monotypic
Sternarchorhynchus was followed by subsequent
authors (e.g., Eigenmann & Allen, 1942; Fowler, 1951)
until Fern?ndez-Y?pez (1967: 18) resurrected S.
mormyrus and S. curvirostris from the synonymy of S.
oxyrhynchus based on differences in external features,
albeit on the basis of misidentified specimens in the
case of the purported S. curvirostris and probably also
for S. mormyrus (see Remarks under that species).
The results of our study, nonetheless, confirm the
distinctiveness of those two nominal species with
respect to S. oxyrhynchus.
Eigenmann (1912: 438) and Ellis (1913: 141)
reported S. oxyrhynchus from Amatuk and Warraputa
in the Essequibo River system of Guyana. As detailed
above, none of the samples of Sternarchorhynchus
that we examined from the river systems of the
Guianas proved to be S. oxyrhynchus. Examination of
the material that served, at least in part, as the basis
of the Eigenmann and Ellis records (CAS 72248 for-
merly CM 1807; CAS 72246, formerly IU 12590) have
shown that they are S. freemani, a species described
as new in this study.
Material examined
GUYANA. Essequibo River, no specified locality
(both locality information and possible number of
specimens in original description problematic; see
under Remarks; photograph and radiograph
of type examined, with meristic and morphometric
data provided by P. Bartsch, ZMB); ZMB 4086, 1
(469; type of Sternarchus oxyrhynchus M?ller &
Troschel).
VENEZUELA. Bolivar: R?o Orinoco, approximately
50 km above mouth of R?o Cuchivero (7?40?N,
65?57?W); ANSP 162670, 4 (268?290). R?o Orinoco,
near mouth of R?o Caura (7?38?N, 64?52?W); ANSP
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 333
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
163044, 1 (283). Delta Amacuro: R?o Orinoco, shallow
river, north side of river across from Isla Tres Ca?os,
131.8 nautical miles (= 243.8 km) from sea buoy
(8?39?48?N, 62?01?W); USNM 228787, 8 (1 CS, 207?
314). R?o Orinoco, deep river channel, at Isla Tres
Ca?o, 130 nautical miles (= 240.5 km) upstream from
sea buoy (8?40?N, 61?59?W); USNM 228788, 1 (348);
MBUCV 10886, 2 (227?297). R?o Orinoco, north
shore, in front of Isla Tres Ca?os (approximately
8?39?48?N, 62?01?W); MBUCV 11853, 1 (305);
MBUCV 10691, 1 (250). MBUCV 12079, 4 (235?
275).
STERNARCHORHYNCHUS RETZERI SP. NOV.
(FIGS 63?65; TABLE 11)
Sternarchorhynchus cf. roseni ? Crampton, 2007: 320,
fig. 11.13c [sexual dimorphism in form of anterior
portion of dentary].
Diagnosis: Sternarchorhynchus retzeri is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
Figure 64. Sternarchorhynchus retzeri sp. nov., holotype, sexually dimorphic male demonstrating modifications of
dentary and dentary dentition, 297 mm total length, MCP 41636; Brazil, Amazonas, Rio Solim?es, Rio Tef?, Tef?.
Figure 65. Sternarchorhynchus retzeri sp. nov., female, 382 mm total length, MCP 41635; Brazil, Amazonas, Rio
Solim?es.
334 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
along the mid-dorsal region of the body, the lateral
line that extends posteriorly to the base of the caudal
fin, the presence of a narrow, more lightly coloured
band of mid-dorsal pigmentation on the head and
mid-dorsal region of the body extending posteriorly to
the origin of the electroreceptive filament and some-
times beyond that point, the distinct band of dark
pigmentation along the distal third to half of most of
the anal fin and covering most of the posterior rays on
that fin, the possession of eight to 11 teeth on the
premaxilla, five to nine teeth in the outer tooth row of
the dentary, one to two teeth in the inner tooth row of
the dentary, 17?25 anterior unbranched anal-fin rays,
198?225 total anal-fin rays, 14?18 caudal-fin rays, 15
precaudal vertebrae, the greatest body depth (8.3?
10.1% of LEA), the preanal distance (13.0?15.2% of
LEA), the caudal length (7.1?10.3% of LEA), the head
width (15.9?18.7% of HL), the head depth at the eye
(21.4?27.7% of HL), the head depth at the nape (34.1?
41.8% of HL), the snout length (65.4?71.2% of HL),
the distance from the posterior naris to the eye (57.3?
74.0% of HL), the distance from the posterior naris to
the snout (5.7?7.0% of HL), the eye diameter (2.5?
3.4% of HL), the postocular distance (31.6?34.9% of
HL), the height of the branchial opening (10.0?12.5%
of HL), the pectoral-fin length (34.4?39.1% of HL),
and the tail depth (15.3?15.8% of caudal length).
Description: Morphometric data for holotype and
paratypes in Table 11.
Lateral line extending to base of caudal fin, but
absent on fin. Snout elongate, compressed and
straight to very slightly curved ventrally distally.
Posterior naris closer to tip of snout than to anterior
margin of eye. Branchial opening restricted and situ-
ated slightly anterior to vertical through pectoral-fin
origin. Location of anus and urogenital papilla onto-
genetically variable and apparently sexually dimor-
phic. Openings in smaller individuals positioned
along vertical located slight distance posterior of ver-
tical through rear margin of orbit. Anus and urogeni-
tal papilla located at vertical slightly anterior of
anterior margin of orbit in mature females and also in
mature males lacking patch of large teeth at anterior
of dentary. Males with patch of large teeth at anterior
of dentary with anus and urogenital papilla posi-
tioned further anteriorly approximately at vertical
one-third of distance between anterior margin of eye
and tip of snout. Combined opening relatively
rounded in juveniles and somewhat to distinctly hori-
zontally elongate in larger specimens.
Premaxilla of small size, somewhat rounded, with
eight to 11 teeth (N = 3). Dentary sexually dimorphic.
Dentary in mature males extended further anteriorly
than in females and juveniles and with anterior
portion widened transversely into bulbous structure
rounded from dorsal view and bearing series of
enlarged, posteriorly recurved teeth on dorsal surface.
Dentary bearing two irregular tooth rows with
approximately five to nine teeth present in outer row
and one to two in inner row (N = 3). Mouth terminal
with rictus located anterior to vertical through pos-
terior naris.
Branchiostegal rays five; with first to third rays
relatively narrow and elongate and fourth and fifth
branchiostegals large and broad. Precaudal vertebrae
16 (12?13 anterior; three to four transitional, N = 10).
Pectoral-fin rays ii + 12?15 [ii + 14] (N = 20). Anal-
fin origin located slightly posterior of vertical through
anterior margin of opercle. Anterior unbranched
anal-fin rays 17?27 [27] (N = 12). Total anal-fin rays
198?225 [225] (N = 14); number of rays apparently
increases ontogenetically based on correlation
between increased body length and greater numbers
of rays in examined samples. Scales above lateral line
at midbody ten to 11 [10] (N = 20). Scales along
mid-dorsal region of body readily apparent. Origin
of midsaggital electroreceptive filament located
approximately at 67% of TL. Filament typically
extending posteriorly to vertical through posterior
terminus of base of anal fin. Tail compressed and of
moderate length, ending in small and elongate caudal
fin. Caudal-fin rays 14?18 (N = 13).
Coloration in alcohol: Overall ground coloration
ranging from light to dark brown. Head and body
with dark chromatophores relatively densely scat-
tered over surfaces. Relative size of chromatophores
and intensity of pigmentation greater in overall
darker specimens. Snout with variably distinct,
narrow band of pigmentation somewhat darker than
ground coloration extending anteriorly from region
slightly forward of orbit to, or slightly short of, ante-
rior portion of snout. Band of dark pigmentation on
snout borders narrow, lightly coloured, mid-dorsal
band on head; lightly pigmented band apparent even
in overall darkly pigmented specimens. Ventral
margin of snout somewhat darker than lateral
surface of snout in some specimens. Body pigmenta-
tion slightly darker dorsally, but with mid-dorsal,
more lightly coloured stripe extending from stripe on
head posteriorly onto basal portions of electrorecep-
tive filament and then to varying degrees further
posteriorly.
Pectoral fin coloration ranging from dusky to dis-
tinctly dark, with pigmentation more pronounced
over fin rays and distally. Anal fin with distinct band
of dark pigmentation along distal third to half of fin
along most of its length, but with dark pigmentation
covering nearly all of shorter fin rays posteriorly.
Caudal-fin rays dark.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 335
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Distribution: Sternarchorhynchus retzeri is broadly
distributed across the Amazon basin from the Rio I?a
basin in the western portions of Amazonas, Brazil, to
the Rio Trombetas in Par?, Brazil (Fig. 63).
Electrical organ discharge: Crampton & Albert (2006:
688) reported that S. retzeri (identified by those
authors as S. cf. roseni) had an EOD resembling their
type B, but ?in which the descending voltage curve has
no, or only a very slight, outward inflection giving the
waveform an asymmetrical aspect in the horizontal
plane?. In light of this difference they proposed that it
be separated as a type C EOD pattern.
Secondary sexual dimorphism: Specimens of S. retzeri
examined in this study demonstrate a striking sexual
dimorphism in the form of the dentary and in the
position of the anus and urogenital opening. At least
some males have the dentary extended further ante-
riorly and widened transversely into a dorsally
bulbous structure that is distinctly rounded from
dorsal view and bears a series of enlarged, posteriorly
recurved teeth (Crampton, 2007: fig. 11.13c; species
identified therein as S. cf. roseni). Juveniles and
adults without these elaborations instead have the
anus and urogenital opening positioned approxi-
mately along the vertical through the eye. Males as
evidenced by the presence of a well-developed patch of
teeth on the anterior portion of the dentary have
these structures instead significantly shifted anteri-
orly and positioned within the region delimited by the
verticals falling one-quarter to one-third of the dis-
tance from the anterior margin of the orbit to the tip
of the snout.
Geographical variation: Nearly all specimens of S.
retzeri examined in this study have the termination of
the electroreceptive filament located at the vertical
through the posterior terminus of the base of the anal
fin. One possible specimen of the species captured in
the Rio Negro (FMNH 115484), has the filament
extending somewhat more posteriorly for a distance of
about four scales beyond the vertical through the
posterior termination of the base of the anal fin. This
specimen is a mature male as evidenced by the
gonads, but has the anus and urogenital papilla ante-
riorly positioned along a vertical approximately one-
third of the distance between the anterior margin of
the orbit and the tip of the snout. This anterior
position of the anus and urogenital papilla occurs
elsewhere in S. retzeri only in mature males with a
distinct batch of enlarged dentition on the anterior
portion of the dentary. The specimen from the Rio
Negro may represent a male of this species without
such modifications of the anterior portions of the
dentary and associated dentition, a situation that
occurs in males of some congeners. Additional
samples are necessary to determine whether it rep-
resents a geographical variant, possible differential
expression of secondary sexual characters in males
because of seasonality in the presence of such dentary
modifications, or an undescribed species.
Etymology: The specific name, retzeri, is in honour of
Michael Retzer of the Illinois Natural History Survey
who provided invaluable assistance through the years
to both authors in the course of this and other
research projects.
Material examined
Holotype: ? BRAZIL. Amazonas: Rio Tef?, Toco Preto,
Tef? (3?47?19?S, 64?59?54?W), collected by W. G. R.
Crampton, 25.x.1999; MCP 41636, 1 (372).
Paratypes: ? BRAZIL. Amazonas: Rio Tef?, Toco Preto,
Tef? (3?47?19?S, 64?59?54?W), collected by W. G. R.
Crampton, 22?25.x.1999; MCP 41635, 10 (281?390).
Nontype specimens: ? BRAZIL. Amazonas: FMNH
115481, 1 (279), FMNH 115504, 1 (222); R?o I?a,
between Paran? do Curumim and Rio Solim?es,
between towns of Bet?nia and S?o Ant?nio do I?a
(3?8?48?S, 68?02?07?W). FMNH 115484, 1 (327); Rio
Negro between Paran? Cantagalo and Paran? On?as,
between S?o Francisco and S?o Francisco de Assis
(1?44?22?S, 61?24?56?W). MZUSP 55847, 1 (200), R?o
Negro, 24.4 km below Paran? Aliaque (1?13?32?S
62?13?49?W). INPA 27493 1 (374); Rio Negro, Lago do
Prato, Anavilhanas. USNM 375475, 1 (270); Rio
Solim?es (3?35?43?S, 61?07?16?W). MZUSP uncat.;
1 (197), Rio Solim?es, below Purus (3?36?25?S,
61?19?40?W). MZUSP 56161, 2 (240?290), Rio
Solim?es, 15.4 km below Paran? do Taiacutuba
(2?36?24?S 65?44?23?W). INPA 27490, 1 (362); INPA
17607, 1 (237); Rio Solim?es, Ilha da Machantaria.
INPA 17606, 1 (242); Rio Solim?es. INPA 17604, 1
(308); Rio Purus, at Beruri. INPA 17605 2 (190?279);
Rio Solim?es, Costa do Marimba, Ilha do Careiro.
Par?: FMNH 115515, 3 (188?236); Rio Amazonas
between Paran? de Santa Rita and Rio Trombetas,
between towns of Jurut? and ?bidos (1?56?7?S,
55?41?19?W). USNM 373027, 3 (186?286); Rio Trom-
betas, 9.9 km above Vila Aracu? (1?30?48?S,
56?10?19?W).
STERNARCHORHYNCHUS ROSENI MAGO-LECCIA
(FIGS 66?68; TABLE 12)
Sternarchorhynchus roseni (nomen nudum), Marrero
& Taphorn, 1991: 129 [use of manuscript name; sec-
ondary sexual dimorphism in species discussed]. ?
336 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Machado-Allison & Moreno, 1993: 88 [use of manu-
script name; Venezuela, Guarico, R?o Orituco].
Sternarchorhynchus roseni Mago-Leccia, 1994: 99,
fig. 92 [type locality: Venezuela, R?o Orinoco basin,
Estado Apure, R?o Apure in front of Jarina, near San
Fernando de Apure]. ? Taphorn et al., 1997: 80 [Ven-
ezuela]. ? Campos-da-Paz, 2000: 528 [recognized as
valid species in key to species of Sternarchorhynchus].
? Albert, 2003: 501 [in listing of members of Sterna-
rchorhynchus]. ? Lasso et al., 2004b: 142 [R?o Orinoco
basin in Colombia and Venezuela]. ? Lasso et al.,
2004a: 181 [Venezuela; R?o Orinoco basin]. ?
Machado-Allison, 2006: 26 [Venezuela]. ? Crampton,
2007: 289 [widespread in Orinoco basin; not cited
occurrence in Amazon].
Diagnosis: Sternarchorhynchus roseni is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, having the scales along the mid-dorsal
portion of the body anterior to the origin of the
electroreceptive filament sparse and covered by skin,
the presence of a more lightly coloured, narrow band
of mid-dorsal pigmentation on the head and mid-
dorsal region of the body extending posteriorly to the
origin of the electroreceptive filament and sometimes
beyond that point, the possession of a total of eight to
11 teeth on the dentary, 16 precaudal vertebrae,
19?27 anterior unbranched anal-fin rays, 193?210
total anal-fin rays, the greatest body depth (8.6?10.9
of LEA), the caudal length (10.7?12.8 of LEA), the
head depth at the nape (40.1?46.3 of HL), the head
depth at the eye (23.0?29.9 of HL), the head width
(19.7?23.0 of HL), the distance from the posterior
naris to the snout (6.0?8.4 of HL), the distance from
the posterior naris to the eye (49.8?63.4 of HL), the
postocular distance (34.0?40.7 of HL), the pectoral-fin
length (34.4?41.0 of HL), and the tail depth (11.0?
16.1 of caudal length).
Figure 66. Sternarchorhynchus roseni, sexually dimorphic male demonstrating modifications of dentary and dentary
dentition, 383 mm total length, MBUCV 19844; Venezuela, Apure, R?o Apure.
Figure 67. Sternarchorhynchus roseni, female, 377 mm total length, LACM 43252-3; Venezuela, Delta de Amacuro, R?o
Orinoco.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 337
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Description: Morphometric data for holotype and
paratypes in Table 12.
Lateral line extending to base of caudal fin, but
absent on fin. Snout elongate, compressed and
slightly curved ventrally, more so distally. Posterior
naris located closer to tip of snout than to anterior
margin of eye. Branchial opening restricted and situ-
ated slightly anterior to vertical through pectoral-fin
origin. Location of anus and urogenital papilla appar-
ently sexually dimorphic. Openings positioned within
range between verticals running slightly anterior to
slightly posterior to eye in smaller individuals,
females, and mature males lacking expanded dentary
and patch of enlarged dentition on dentary. Anus and
urogenital aperture much more anteriorly positioned
in males with definite patch of enlarged dentition on
dentary and located between verticals approximately
one-quarter to one-third distance between anterior
limit of eye and tip of snout. Combined opening for
anus and urogenital papilla slightly horizontally elon-
gate in males with well-developed patch of teeth on
dentary; opening more rounded in other examined
specimens.
Premaxilla of small size, somewhat rounded, with
seven to eight teeth (N = 2). Dentary with two rows of
teeth with total of eight to 11 teeth (N = 2). Dentary
form sexually dimorphic. Dentary in some males
extending further anteriorly than in females and
widened transversely into dorsally bulbous structure,
rounded from dorsal view and bearing series of
enlarged, slightly posteriorly recurved teeth. Mouth
terminal with rictus located anterior to vertical
through anterior naris in juveniles, posterior of that
vertical in males with enlarged dentary with patch of
teeth, but still located distinctly anterior of vertical
through posterior naris.
Branchiostegal rays five; with first to third rays
relatively narrow and elongate and fourth and fifth
rays large and broad. Precaudal vertebrae 16 (12?13
anterior, three to four transitional; N = 10).
Pectoral-fin rays ii + 11?14 [ii + 12] (N = 25). Anal-
fin origin located slightly posterior of vertical through
anterior margin of opercle. Anterior unbranched anal-
fin rays 19?27 (N = 18). Total anal-fin rays 193?210
[208] (N = 21); number of fin rays apparently
increases ontogenetically based on correlation
between greater body size and increased numbers of
fin rays within examined samples. Scales above
lateral line at midbody seven to 12 [12] (N = 25).
Scales along mid-dorsal region of body somewhat
sparse and not readily apparent on body surface.
Origin of midsaggital electroreceptive filament
located approximately at 62% of TL. Filament extend-
ing one to two scales posterior of vertical through
Figure 68. Map of central and northern South America showing geographical distribution of Sternarchorhynchus roseni,
Sternarchorhynchus schwassmanni sp. nov. (1 = holotype locality), Sternarchorhynchus severii, and Sternarcho-
rhynchus starksi sp. nov. (2 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).
338 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
posterior terminus of base of anal fin. Tail compressed
and of moderate length, ending in small and elongate
caudal fin. Caudal-fin rays 12?16 [16] (N = 14).
Coloration in life: In his original description of S.
roseni, Mago-Leccia (1994: 102) reported that recently
collected males from the R?o Apure, had a ?dark,
almost black? life coloration with a dark snout and
hyaline midsaggital electroreceptive filament (the
thong of that author). Females collected together with
the males were ?gray with a snout clear which had a
dark line contacting the midline pale stripe? and the
filament was reported as ?grayish? and the anal fin
was reported to have a ?dark border?.
Coloration in alcohol: Overall ground coloration light
to dark brown. Head and body covered with relatively
densely packed dark chromatophores. Size of indi-
vidual chromatophores and intensity of pigmentation
greater in overall darker specimens. Snout with vari-
ably distinct, narrow band of somewhat darker pig-
mentation extending forward from region anterior of
orbit and reaching to anterior portion of snout in
many specimens. Anterior portion of snout darker
Table 12. Morphometric data for holotype (H), and paratypes of Sternarchorhynchus roseni, Sternarchorhynchus
schwassmanni, and Sternarchorhynchus severii
S. roseni S. schwassmanni S. severii
Range Mean H Paratype H Paratypes Mean
Total length (mm) 154?417 (N = 17) ? 98.5 115.8 161 67.0?169 (N = 12) ?
Length to end of anal
fin (mm)
138?375 (N = 17) ? 87.4 111.7 145 61.7?149 (N = 12) ?
Head length (mm) 27.7?53.9 (N = 17) ? 19.7 23.0 23.7 9.0?28.6 (N = 12) ?
Caudal length (mm) 14.9?46.8 (N = 15) ? 7.0 ? 14.6 5.7?14.6 (N = 12) ?
Per cent of length to end of anal fin
Anal-fin base 82.6?97.7 (N = 17) 87.0 83.9 80.2 85.5 78.9?89.5 (N = 12) 85.0
Distance snout to anus 8.0?13.2 (N = 17) 11.1 11.8 10.6 19.6 10.0?13.5 (N = 12) 11.6
Preanal-fin distance 11.4?15.0 (N = 17) 13.7 15.2 13.6 12.0 12.9?16.7 (N = 12) 14.4
Prepectoral-fin distance 16.2?20.7 (N = 17) 19.1 22.2 21.8 17.0 16.4?21.2 (N = 12) 19.1
Greatest body depth 8.6?10.9 (N = 17) 9.8 12.7 12.4 13.5 12.7?14.0 (N = 12) 13.4
Head length 16.0?20.9 (N = 17) 19.0 22.5 20.6 16.4 16.4?20.7 (N = 12) 18.5
Caudal length 10.7?12.8 (N = 15) 11.6 8.0 ? 10.1 7.7?11.3 (N = 12) 9.7
Per cent of head length
Anus to anal-fin insertion 7.0?20.0 (N = 17)
27.5?32.5 (N = 2)
12.230.0 10.5 14.4 15.0 7.8?19.9 (N = 12) 12.3
Pectoral-fin length 34.4?41.0 (N = 19) 37.5 35.5 38.3 66.6 48.7?59.8 (N = 12) 52.2
Head depth at eye 23.0?29.9 (N = 19) 26.9 31.6 30.4 35.4 31.7?36.0 (N = 5) 34.4
Head depth at nape 40.1?46.3 (N = 19) 43.3 49.6 49.5 63.2 53.8?72.0 (N = 12) 61.2
Head width 19.7?23.0 (N = 19) 21.0 25.6 22.6 23.7 23.6?26.0 (N = 5) 24.5
Snout length 56.7?70.6 (N = 19) 65.8 56.8 57.3 50.2 44.7?53.2 (N = 12) 49.4
Posterior naris to snout 6.0?8.4 (N = 19) 7.5 9.6 10.2 8.0 7.4?10.0 (N = 5) 8.3
Posterior naris to eye 49.8?63.4 (N = 19) 57.5 44.2 45.4 65.5 48.8?67.2 (N = 12) 58.8
Mouth length 4.1?6.4 (N = 19) 5.1 6.3 5.7 9.7 7.8?9.8 (N = 12) 8.9
Internarial distance 2.5?3.5 (N = 18) 3.0 3.6 3.0 5.0 4.0?6.0 (N = 12) 5.1
Eye diameter 2.3?4.2 (N = 19) 3.1 6.4 5.3 8.0 6.2?9.2 (N = 12) 7.9
Interocular width 4.8?7.8 (N = 19) 6.0 9.1 9.7 8.6 6.0?15.3 (N = 12) 10.2
Postocular distance 34.0?40.7 (N = 19) 37.1 42.4 43.3 56.8 45.2?54.2 (N = 12) 49.6
Branchial opening 9.4?14.3 (N = 19) 12.1 14.8 15.2 21.3 15.4?21.7 (N = 12) 19.2
Per cent of caudal length
Tail depth 11.0?16.1 (N = 15) 13.6 22.3 ? 17.3 14.5?24.1 (N = 12) 18.8
Caudal-fin length 16.8?29.5 (N = 15) 21.9 41.7 ? 37.2 28.6?49.3 (N = 12) 39.8
Sexually dimorphic features for S. roseni are presented as two entries. First entry is data for all specimens other than
sexually dimorphic mature males. Information for sexually dimorphic male in second entry based on two specimens of
385?405 mm total length. Number of specimens indicated in parentheses.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 339
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
than adjoining areas in some males with well-
developed patches of enlarged dentition on lower jaw.
Dark band on lateral surface of snout apparent even
in overall darkly pigmented specimens and forms
lateral margin of narrow, lightly coloured, mid-dorsal
band on snout. Lightly coloured mid-dorsal band on
head expands laterally along dorsal portion of pos-
tocular region of head and continuous posteriorly with
narrow, mid-dorsal lightly coloured stripe on body.
Body pigmentation overall slightly darker dorsally,
but with narrow, lightly coloured mid-dorsal stripe
extending from rear of head posteriorly onto basal
portions of electroreceptive filament and then to
varying degrees further posteriorly in various
specimens.
Pectoral-fin coloration ranging from nearly hyaline
in many specimens to dusky in darker individuals,
with dark chromatophores overlying pectoral-fin rays.
Anal-fin pigmentation apparently sexually dimorphic.
Anal fin completely hyaline in most examined speci-
mens, including apparently mature females. Some of
darker individuals with overall hyaline anal fins
having basal portions of rays outlined by series of
dark chromatophores and forming very faint band.
Males with anteriorly and laterally expanded dentary
with patch of enlarged dentary teeth have distal half
of most of anal fin darker and forming distinct band;
band extends across all rays in narrower posterior
portion of fin. Caudal-fin pigmentation variable, with
coloration of rays ranging from somewhat to distinctly
dark and with pigmentation always more developed
on basal portions of rays. Some males with expanded
dentaries have additional distal dark pigmentation on
caudal fin.
Distribution: Examined specimens of S. roseni all
originated in the central portions of the R?o Orinoco
system in Colombia and Venezuela (Fig. 68). Lasso
et al. (2004b: 142) reported the species as inhabiting
other portions of the basin ranging from the state of
Delta Amacuro in eastern Venezuela to the R?o Meta
system in the western portions of the R?o Orinoco
system.
Ecology: Specimens of S. roseni collected at Ca?o
Bravo in the R?o Apure drainage of Venezuela came,
in part, from a white water habitat over a substrate
of sand and clay covered with leaf litter and at water
depths of up to 1.5 m (de Santana et al., 2006: 279).
Secondary sexual dimorphism: Sternarchorhynchus
roseni demonstrates sexual dimorphism of the ante-
rior portion of the dentary and associated dentition
comparable to that present in some congeners. The
species also demonstrates a striking sexual dimor-
phism in the position of the anus and urogenital
papilla. Females along with juveniles have the anus
and urogenital papilla positioned approximately at
the vertical through the eye. Mature males, as evi-
denced by the presence of a well-developed patch of
enlarged teeth on the expanded anterior portion of
the dentary, have the anus and urogenital papilla
instead significantly shifted anteriorly and positioned
in the region delimited by verticals running one-
quarter to one-third of distance from the anterior
margin of the orbit to the tip of the snout.
Remarks: As aforementioned under Coloration in life,
Mago-Leccia (1994) reported a distinct sexual dimor-
phism in the coloration in S. roseni, with males being
much darker than females. Our samples demonstrate
a significant degree of variation in overall coloration
with the species. We found, however, that in pre-
served samples the mature males with well-developed
patches of enlarged teeth on the expanded dentary
had only a slightly darker coloration than did females
collected at the same time. It is possible that the
distinct sexual dimorphism in pigmentation reported
by Mago-Leccia (1994) for S. roseni is apparent only
in life or is limited to the breeding season.
Material examined
COLOMBIA. R?o Meta, unspecified localities; IAVHP
2981, 1 (221), IAVHP 6278, 1 (129).
VENEZUELA. Apure: R?o Apure, near of mouth of
R?o Manglar (approximately 7?52?N, 67?36?W); MCNG
50521, 1 (192). R?o Apure, near San Fernando de
Apure; INHS 28403, 1 (240); R?o Apure (7?16.26?N,
71?5.20?W). AMNH 58665, 2 (233?253; paratypes),
MBUCV 15809, 6 (212?273; paratypes), MBUCV
19839, 8 (144?256; paratypes). R?o Apure, 1 km
upstream from San Fernando de Apure; MBUCV
19843, 1 (400). R?o Apure, 3 to 5 km downstream from
bridge of San Fernando de Apure; MBUCV 19844, 1
(383). R?o Apure, near Isla del Medio; MBUCV 20025,
2 (208?289; paratypes). R?o Apure, between mouth of
R?o Portuguesa and San Fernando de Apure airport
(7?54?00?N, 67?32?00?W); ANSP 165215, 2 (202?330).
R?o Apure, near San Fernando de Apure; MCNG
24068, 1 (216). R?o Apure at confluence with R?o
Portuguesa; MBUCV 7562, 1 (143; paratype). R?o
Meta, upstream from confluence with R?o Orinoco;
MBUCV 15722, 1 (171; paratype). MBUCV 15807, 5
(170?245; paratypes), MBUCV 15811, 1 (117;
paratype); R?o Apure, in front of Isla Apurito (8?00?N,
67?31?W). R?o Apure, at Jarina (7?56?N, 67?30?W).
MCNG 52591, 18 (115?172), R?o Aruaca, Ca?o
Bucaral; MBUCV 20037, holotype (267), MBUCV
20066, 1 (166; paratype); MBUCV 15808, 2 (154?247;
paratypes). R?o Arauca, mouth of Ca?o Bucaral;
MBUCV 15810, 1 (108; paratype). R?o Apure, at La
Rompia; MBUCV 15813, 1 (180; paratype). R?o Apure,
340 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
10 km downstream of San Fernando de Apure
(7?86?39?N, 67?39?17?W); MCNG 13875, 5 (161?285).
R?o Apure, mouth of R?o Portuguesa near San
Fernando de Apure (7?95?00?N, 67?52?78?W); MCNG
14040, 1 (206), MCNG 14041, 1 (145). R?o Portuguesa,
between Estudos Barinas and Guarico; MCNG 51457,
2 (175?323), MCNG 51458, 5 (172?240), MCNG
51459, 3 (166?222). R?o Apure, Ca?o Caujarito;
MCNG 45131, 2 (152?221). R?o Apure, Ca?o Caicara,
where crossed by bridge on road from Mantecal
(7?22?N, 69?21?W); USNM 260248, 4 (164?222).
Barinas: R?o Apure, mouth of R?o Portuguesa; MCNG
52552, 3 (185?335), MCNG 52546, 1 (326). R?o Mas-
parro, 5 km north-west from Libertad to Barinas;
INHS 29916, 1 (255). R?o Apure, Ca?o Bravo
(8?00?00?N, 67?98?33?E); MCNG 49176, 1 (196),
MCNG 49284, 1 (171), MCNG 49314, 3 (131?180),
MCNG 49341, 1 (168), MCNG 49462, 1 (78), MCNG
49614, 1, (184), MCNG 51727, 1 (96), MCNG 51747, 4
(105?170), MCNG 51770, 1 (228), MCNG 51790, 2
(137?170), MCNG 52106, 1 (310), MCNG 52233, 8
(123?222), MCNG 52264, 1 (52). Bolivar: R?o Orinoco,
near Puerto Las Majadas, at confluence with R?o
Caura; MBUCV 15697, 1 (217). R?o Portuguesa
(9?06?67?N, 69?50?00?W); MCNG 15827, 3 (91?120).
R?o Orinoco, near Isla de Farjado (8?22?N, 62?42W);
USNM 228879, 1 (410). Delta de Amacuro: R?o
Orinoco, LACM 43252?3, 4 (186?377). R?o Orinoco,
old shipping channel south of Isla Portuguesa;
MBUCV 10411, 1 (235; paratype). R?o Orinoco, down-
stream from El Concejo; MBUCV 12201, 3 (228?260).
R?o Orinoco, at Isla Tres Ca?os (8?39?48?N,
61?58?40?W); USNM 228786, 1 (226). Guarico: R?o
Orituco; MBUCV 5491, 1 (93; paratype). R?o Orinoco,
mouth of Ca?o Guine (8?39?54?N, 62?02?06?W);
USNM 228880, 2 (333?413). R?o Orituco (8?52?N,
67?18?W); USNM 260246, 1 (123). R?o Guarico, at
Flores Moradas ranch approximately 3?4 km east of
road from Calabozo to San Fernando de Apure
(8?27?N, 67?25?W); USNM 260249, 1 (242).
STERNARCHORHYNCHUS SCHWASSMANNI SP. NOV.
(FIGS 68, 69; TABLE 12)
Diagnosis: Sternarchorhynchus schwassmanni is dis-
tinguished from congeners by the following combina-
tion of characters: a short gape that terminates
posteriorly at, or slightly short of, the vertical through
the anterior nares, in having the scales along the
mid-dorsal portion of the body anterior to the origin of
the electroreceptive filament sparse and covered by
skin to varying degrees, the presence of a more lightly
coloured, narrow band of mid-dorsal pigmentation on
the head and mid-dorsal region of the body extending
posteriorly to the origin of the electroreceptive fila-
ment and sometimes beyond that point, the extension
of the dorsal filament to a point one or two scales
posterior of the vertical through the posterior termi-
nus of the base of the anal fin, the possession of ten
teeth in the outer tooth row on the dentary, 15 pre-
caudal vertebrae, 25?26 anterior unbranched anal-fin
rays, nine to ten scales above the lateral line at the
midbody, 164?166 total anal-fin rays, the greatest
body depth (12.4?12.7% of LEA), the length of
the base of the anal fin (80.2?83.9% of LEA), the
prepectoral-fin distance (21.8?22.2% of LEA), the
head depth at the nape (49.5?49.6% of HL), the snout
length (56.8?57.3% of SL), the mouth length (5.7?
6.3% of HL), the interocular width (9.1?9.7% of HL),
the eye diameter (5.3?6.4% of HL), the distance from
the posterior naris to the eye (44.2?45.4% of HL), the
postocular distance (42.4?43.3% of HL), the height of
the branchial opening (14.8?15.2% of HL), and the
pectoral-fin length (35.5?38.2% of HL).
Description: Morphometric data for examined speci-
mens in Table 12.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
curved ventrally distally. Mouth terminal and rela-
tively small, with rictus located slightly anterior to
Figure 69. Sternarchorhynchus schwassmanni sp. nov., holotype, female, 98.5 mm total length, MZUSP 95633,
Brazil, Par?, Rio Araguaia.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 341
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
vertical through anterior naris. Anus and urogenital
papilla located ventral to head. Those structures situ-
ated along, or slightly anterior of, vertical through
eye. Combined opening for anus and urogenital
papilla ovoid.
Premaxilla with six to eight teeth (N = 2) apparent
in whole specimens. Dentary with two tooth rows;
outer row with ten teeth and inner row with two to
three teeth (N = 2).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15 (12 anterior; three
transitional; N = 2).
Pectoral-fin rays ii + 12?13 [ii + 13] (N = 2). Anal-fin
origin located anterior to vertical through margin of
opercle. Anterior unbranched anal-fin rays 25?26 [25]
(N = 2). Total anal-fin rays 164?166 [166] (N = 2).
Scales above lateral line at midbody nine to ten [9]
(N = 2). Scales present but sparse and covered to
varying degrees by skin along mid-dorsal line to
origin of midsaggital electroreceptive filament. Origin
of electroreceptive filament located approximately at
65% of TL. Filament extending posteriorly to point
one to two scales anterior of vertical through posterior
terminus of base of anal fin. Tail compressed and
short, ending in small, moderate, posteriorly rounded
caudal fin. Caudal-fin rays 16 (N = 1).
Coloration in alcohol: Overall coloration brown. Head
brown overall other than for slightly lighter region on
midlateral surface of snout. Fleshy pad on anterior of
dentary largely unpigmented. Darker pigmentation
on snout forms lateral margin of lightly coloured,
mid-dorsal stripe on snout. Mid-dorsal stripe contin-
ues posteriorly and expands very slightly laterally
above postocular portion of head. Mid-dorsal stripe on
head continuous posteriorly with narrow, lightly
coloured, mid-dorsal stripe that extends posteriorly
from rear of head to, or beyond, origin of electrore-
ceptive filament. Posterior portion of tail darker than
remainder of body. Pectoral fin dusky with rays over-
lain by dark chromatophores. Anal fin dusky with
rays overlain by dark chromatophores. Caudal fin
dark basally, but with hyaline posterior margin.
Distribution: Sternarchorhynchus schwassmanni is
only known from the type locality in the Rio Araguaia
of eastern Brazil (Fig. 68).
Etymology: The species name, schwassmanni, is in
honour of Horst O. Schwassmann, University of
Florida, for his contributions to the knowledge of
Neotropical electric knifefishes.
Secondary sexual dimorphism: No sexual dimorphism
was apparent in the limited examined sample of S.
schwassmanni.
Remarks: One of the striking attributes of S. schwass-
manni is its relatively small size at maturity. The
98.5 mm TL holotype is a female with developed
white eggs and the 115.8 mm TL paratype is a male
with developed testes.
Material examined
Holotype: ? BRAZIL. Par?: Rio Araguaia, small
stream between S?o Jo?o do Araguaia (5?23?S,
48?46?W) and S?o Bento (5?28?S, 48?20?W), collected
by R. Stawikowski, 12.xi.1990; MZUSP 95633 (98.5,
female, formerly MHNG 2566.093, in part).
Paratype: ? BRAZIL. Par?: Rio Araguaia, small
stream between S?o Jo?o do Araguaia (5?23?S,
48?46?W) and S?o Bento (5?28?S, 48?20?W), collected
with holotype by R. Stawikowski, 12.xi.1990; MHNG
2566.093, 1 (115.8, male).
STERNARCHORHYNCHUS SEVERII DE SANTANA &
NOGUEIRA (FIGS 68, 70; TABLE 12)
Sternarchorhynchus oxyrhynchus, not of M?ller &
Troschel, Ferreira et al., 1988: 344 [in listing of
species from Rio Mucaja?].
Sternarchorhynchus severii de Santana &
Nogueira, 2006: 89, figs 1b, 2b, c [type locality: Brazil,
Roraima, Rio Mucaja?, below Cachoeira Pared?o].
Figure 70. Sternarchorhynchus severii, holotype, male, 161 mm total length; Brazil, Roraima, Rio Mucaja?.
342 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Diagnosis: Sternarchorhynchus severii is distin-
guished from congeners in the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
along the mid-dorsal region of the body, the lateral
line that extends posteriorly to the base of the caudal
fin, the dorsal filament that extends to a point two
scales beyond the vertical through the posterior ter-
minus of the base of the anal fin, the presence of a
more lightly coloured narrow band of mid-dorsal pig-
mentation on the head and mid-dorsal region of the
body anterior of the origin of the electroreceptive
filament and sometimes extending posteriorly beyond
that point, the dusky anal fin without a distinct dark
band along the distal portions, the possession of nine
to ten premaxillary teeth, seven to eight teeth on the
outer row of the dentary, two to three teeth on the
inner row of the dentary, 24?32 anterior unbranched
anal-fin rays, 161?175 total anal-fin rays, 12?14
caudal-fin rays, the greatest body depth (12.7?14.0%
of LEA), the caudal length (7.7?11.3% of LEA), the
preanal distance (12.0?16.7% of LEA), the distance
from the anus to the anal-fin insertion (7.8?19.9% of
HL), the prepectoral-fin distance (16.4?21.2% of
LEA), the caudal length (7.7?11.3% of LEA), the
snout length (44.7?53.2% of HL), the head depth at
the nape (53.8?72.0% of HL), the height of the bran-
chial opening (15.4?21.7% of HL), the postocular
length (45.2?56.8% of HL), the internarial distance
(4.0?6.0% of HL), the pectoral-fin length (48.7?66.6%
of HL), and the tail depth (14.5?24.1% of caudal
length).
Description: Morphometric data for examined speci-
mens in Table 12.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
slightly curved ventrally distally. Mouth terminal and
relatively small, with rictus located slightly anterior
to vertical through anterior naris. Anus and urogeni-
tal papilla located ventral to head. Those structures
situated within region delimited anteriorly by vertical
less than one orbital diameter anterior of eye and
posteriorly by vertical less than one orbital diameter
posterior of eye. Combined opening for anus and
urogenital papilla circular to longitudinally ovoid.
Premaxilla with nine to ten teeth (N = 6) apparent
in whole specimens. Dentary with two tooth rows;
outer row with seven to eight teeth and inner row
with two to three teeth (N = 6).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15?16 (12?14 ante-
rior; two to four transitional; N = 6).
Pectoral-fin rays ii + 12?13 [ii + 12] (N = 13). Anal-
fin origin located anterior to vertical through margin
of opercle. Anterior unbranched anal-fin rays 24?32
[26] (N = 12). Total anal-fin rays 161?175 [164]
(N = 12). Scales above lateral line at midbody seven
to 12 [9] (N = 13). Scales clearly present along
mid-dorsal line of body to origin of midsaggital
electroreceptive filament. Origin of midsaggital elec-
troreceptive filament located approximately at 65% of
TL. Filament extending posteriorly to point two scales
anterior of vertical through posterior terminus of base
of anal fin. Tail compressed and short, ending in
small, moderate, posteriorly rounded caudal fin.
Caudal-fin rays 12?15 [15] (N = 11).
Coloration in alcohol: Overall coloration brown. Head
brown overall laterally other than for slightly lighter
region on midlateral surface of snout. Fleshy pad on
anterior of dentary less intensely unpigmented than
adjoining regions. Darker pigmentation on dorsolat-
eral portion of snout forms lateral margin of anterior
region of lightly coloured, mid-dorsal stripe on head.
Lightly coloured, mid-dorsal area on head slightly
laterally expanded above orbit and along anterior
portion of postocular region of head and variably
continuous posteriorly with narrow, mid-dorsal lightly
pigmented stripe on body that extends posteriorly to,
or beyond, origin of electroreceptive filament. Pectoral
fin dusky with rays overlain by dark chromatophores.
Anal fin dusky with rays overlain by dark chromato-
phores. Caudal fin very dark basally, but with hyaline
region along rounded posterior margin.
Distribution: Sternarchorhynchus severii is only
known from the type locality in the Rio Mucaja?,
below Cachoeira Pared?o (Fig. 68).
Secondary sexual dimorphism: No sexual dimorphism
was observed in the limited available material of
S. severii.
Ecology: According to Ferreira et al. (1988: 341), the
area where the samples of S. severii were collected is
characterized by steep banks and a shoreline bor-
dered by dense forest. Large amounts of aquatic plans
of the family Podostemonacease were present in the
river, with the water being acidic (pH 5.8) and well
oxygenated (91% saturation).
Remarks: The type series of S. severii and S. caboclo
were collected at the same location. The two species
are readily distinguishable by the number of bran-
chiostegal rays (five versus four, respectively), pig-
mentation of the head and body (with narrow, lightly
coloured stripe extending posteriorly to the origin of
the electroreceptive filament versus mid-dorsal region
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 343
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
of head and body dark, respectively), the pectoral-fin
length (48.7?66.6 versus 31.3?46.9% of HL, respec-
tively), and the head depth at the eye (31.7?36.0
versus 23.3?31.1% of HL, respectively).
Material examined
BRAZIL. Roraima: Rio Mucaja?, below falls of Cach-
oeira Pared?o (approximately 2?57?N, 61?27?W); INPA
22893, 1 (161, male, holotype); INPA 22898, 13
(paratypes; 67?169, 2 cleared and stained).
STERNARCHORHYNCHUS STARKSI SP. NOV.
(FIGS 68, 71; TABLE 13)
Sternarchorhynchus mormyrus, not of Steindachner,
Eigenmann & Bean, 1907: 666 [Brazil, lower Amazon
between Par? (= Bel?m) and Manaus].
Sternarchorhynchus curvirostris, not of Boulenger,
Starks, 1913: 23 [Brazil, Par? (= fish market at
Bel?m].
Diagnosis: Sternarchorhynchus starksi is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the anterior naris, the pres-
ence of a definite series of scales along the mid-dorsal
region of the body, the lateral line extending posteri-
orly to the base of the caudal fin, the presence of a
more lightly coloured, narrow band of mid-dorsal pig-
mentation on the head and mid-dorsal region of the
body extending posteriorly to the origin of the elec-
troreceptive filament and sometimes beyond that
point, the hyaline anal fin without a distal dark band,
the extension of the dorsal filament posteriorly to a
point along the vertical approximately eight scales
posterior of the terminus of the base of the anal fin,
the possession of ten to 13 premaxillary teeth, eight
teeth on the outer row of the dentary, four to five
teeth on the inner row of the dentary, 18?26 anterior
unbranched anal-fin rays, 185?202 total anal-fin rays,
11?14 scales above the lateral line at the midbody,
11?13 caudal-fin rays, the greatest body depth (9.7?
12.5% of LEA), the head length (14.8?18.1% of LEA),
the distance from the snout to the anus (7.0?10.8% of
LEA), the distance from the anus to the anal-fin
origin (8.3?18.3% of LEA), the prepelvic distance
(14.4?18.3% of LEA), the caudal length (12.2?16.5%
of LEA), the snout length (56.3?61.6% of HL), the
distance from the posterior naris to the eye (47.8?
53.7% of HL), the pectoral-fin length (40.6?53.2% of
HL), the head depth at the eye (26.9?36.2% of HL),
the head depth at the nape (50.5?69.3% of HL), the
head width (23.1?28.4% of HL), and the tail depth
(9.9?13.2% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 13.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
slightly to distinctly curved ventrally; degree of cur-
vature more pronounced in larger individuals. Mouth
terminal and relatively small, with rictus located
slightly anterior to vertical through anterior naris.
Anus and urogenital papilla located ventral to head,
with position apparently ontogenetically somewhat
variable. Those structures situated along vertical
approximately four orbital diameters posterior of rear
margin of eye in smaller specimens and approaching,
or along, vertical through eye in larger individuals.
Combined opening for anus and urogenital papilla
longitudinally ovoid.
Premaxilla with ten to 13 teeth (N = 9) apparent in
whole specimens. Dentary with two tooth rows; outer
row with eight teeth and inner row with four to five
teeth (N = 6).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15?16 (12?13 ante-
rior; two to three transitional; N = 13).
Pectoral-fin rays ii + 12?14 [ii + 13] (N = 13). Anal-
fin origin located anterior to vertical through margin
of opercle. Anterior unbranched anal-fin rays 18?26
[22] (N = 13). Total anal-fin rays 185?202 [199]
(N = 11). Scales above lateral line at midbody 11?14
[11] (N = 13). Scales present along mid-dorsal line to
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located
approximately at 56% of TL. Filament extending pos-
teriorly to point eight to ten scales posterior of verti-
cal through posterior terminus of base of anal fin. Tail
compressed and long, ending in small, moderate,
pointed caudal fin. Caudal-fin rays 11?13 (N = 7).
Figure 71. Sternarchorhynchus starksi sp. nov., holotype, 231 mm total length, INPA 28377; Brazil, Par?, Rio Par?.
344 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
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PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 345
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Coloration in alcohol: Overall coloration light brown.
Head with narrow, faint stripe of slightly darker
pigmentation extending anteriorly from orbit for dis-
tance half to two-thirds length of snout. Darker pig-
mentation on snout forms lateral margin of lightly
coloured, mid-dorsal stripe on snout. Lightly coloured
mid-dorsal stripe on snout expands into longitudi-
nally elongate ovoid area above postocular portion of
head. Ovoid region continuous posteriorly with barely
apparent mid-dorsal, lightly coloured stripe that
extends posteriorly from rear of head for varying
degrees, but which falls short of origin of electrore-
ceptive filament. Pectoral fin hyaline to dusky. Anal
fin hyaline. Caudal fin slightly dusky.
Distribution: Samples of S. starksi with definite local-
ity information originated in the easternmost portions
of the Amazon basin or were purchased in the fish
market at Bel?m (Starks, 1913: 4, 23); cited therein
as S. curvirostris). Given the fishing and transporta-
tion technology of that era, it is likely that those
market samples were captured close to that city in
the lowermost portion of the Amazon River (Fig. 68).
Secondary sexual dimorphism: No sexual dimorphism
apparent in limited available samples of S. starksi.
Etymology: The species name, starksi, is in honour of
Edwin Chapin Starks of Stanford University, who in
the early part of the twentieth century collected a
portion of the series that served as the basis for this
description and who made a number of contributions
to our knowledge of the anatomy of fishes.
Remarks: Examination of the specimens (CAS SU
22193; USNM 52542) that served, at least in part, as
the basis for the citation of S. mormyrus from the
lower Amazon between Par? (= Bel?m) and Manaus
(Eigenmann & Bean, 1907: 666) and of S. curvirostris
from the Bel?m region (Starks, 1913: 23) has shown
them to be S. starksi.
Material examined
Holotype: ? BRAZIL. Par?: Rio Par? between Rio Boa
Vista and Rio Tocantins, between towns of Boa Vista
and Abaetetuba (1?45?30?S, 49?29?17?W), collected by
A. M. Zanata et al., 18.xi.1994; INPA 28377 (231,
formerly FMNH 115485).
Paratypes: ? BRAZIL. Par?: Par? (= fish market at
Bel?m), collected by E. C. Starks, 1911; CAS SU
22193, 10 (203?374). Rio Amazonas between Par?
(= Bel?m) to Manaus, collected by J. B. Steere, 1901;
USNM 52542, 2 [229 (tail broken)-267]. R?o Jari,
Monte Dourado, upstream of Rio Amazonas, L.
Py-Daniel et al., 13.xi.1994; MZUSP 58196, 1 (260).
Nontype specimens: ? BRAZIL. Par?: Rio Amazonas,
above Rio Xingu and town of Gurup? (1?28?38?S,
52?04?00?W), USNM 373029, 1 (278 regenerated tail).
Par? (= fish market at Bel?m); AMNH 3776, 1 (307),
AMNH 9869, 1 (259).
STERNARCHORHYNCHUS STEWARTI SP. NOV.
(FIGS 72, 73; TABLE 13)
Sternarchorhynchus curvirostris, not of Boulenger,
Stewart, Barriga & Ibarra, 1987: 37 [Ecuador, R?o
Napo basin].
Diagnosis: Sternarchorhynchus stewarti is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
along the mid-dorsal region of the body, the lateral
line that extends posteriorly to the base of the caudal
fin, the dorsal filament that extends posteriorly to a
vertical approximately eight to ten scales posterior of
the vertical through the posterior terminus of the
Figure 72. Sternarchorhynchus stewarti sp. nov., holotype, 182 mm total length, MUSM 30409; Peru, Amazonas, R?o
Mara?on.
346 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
base of the anal fin, the presence of a more lightly
coloured narrow band of mid-dorsal pigmentation on
the head and mid-dorsal region of the body extending
posterior to the origin of the electroreceptive filament
and sometimes beyond that point, the hyaline to
slightly dusky anal fin without a distinct band of dark
pigmentation either distally or basally, the possession
of seven to eight teeth on the premaxilla, six to seven
teeth on the outer tooth row of the dentary, three to
four teeth on the inner tooth row of the dentary, 16
precaudal vertebrae, 13?15 branched pectoral-fin
rays, 26?34 anterior unbranched anal-fin rays, 180?
191 total anal-fin rays, eight to nine scales above the
lateral line at the midbody, 15?17 caudal-fin rays, the
greatest body depth (11.4?13.7% of LEA), the distance
from the anus to the anal-fin insertion (7.8?13.2% of
HL), the preanal distance (12.0?13.9% of LEA), the
prepectoral-fin distance (18.3?21.8% of LEA), the
caudal length (6.1?7.1% of LEA), the head length
(18.3?21.1% of LEA), the distance from the posterior
naris to the snout (8.1?9.3% of HL), the mouth length
(6.1?7.5% of HL), the snout length (61.7?65.7% of
HL), the internarial distance (2.3?3.3% of HL), the
head width (22.5?25.5% of HL), the head depth at the
nape (50.4?59.0% of HL), the height of the branchial
opening (11.8?14.5% of HL), and the tail depth (19.8?
25.7% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 13.
Lateral line extending posteriorly to base of caudal
fin, but absent on fin. Snout elongate, compressed and
slightly to distinctly curved ventrally. Mouth terminal
and relatively small, with rictus located slightly ante-
rior to vertical through anterior naris. Anus and uro-
genital papilla located ventral to head, with position
apparently ontogenetically somewhat variable. Both
structures positioned along vertical running approxi-
mately two to three orbital diameters posterior of rear
margin of eye in smaller specimens and at, or up to
Figure 73. Map of central and northern South America showing geographical distribution of Sternarchorhynchus
stewarti sp. nov. (1 = holotype locality), Sternarchorhynchus taphorni sp. nov. (2 = holotype locality), Sternarcho-
rhynchus yepezi sp. nov. (3 = holotype locality; 4 = collecting location of possibly conspecific sample from central
Amazon; under Remarks concerning that specimen and second specimen from aquarium trade possibly collected in the
region of Iquitos, Peru), and Sternarchorhynchus villasboasi sp. nov. (5 = holotype locality) (some symbols represent
more than one locality and/or lot of specimens).
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 347
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
one orbital diameter anterior of, vertical running
through anterior margin of eye in larger individuals.
Opening for anus and urogenital papilla ovoid, but
with fleshy puckered margin.
Premaxilla with seven to eight teeth (N = 15)
apparent in whole specimens. Dentary with two tooth
rows; outer row with six to seven teeth and inner row
with three to four teeth (N = 10).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 16 (12?13 anterior;
three to four transitional; N = 25).
Pectoral-fin rays ii + 13?15 [ii + 14] (N = 27). Anal-
fin origin located anterior to vertical through margin
of opercle. Anterior unbranched anal-fin rays 26?34
[27] (N = 20). Total anal-fin rays 179?191 [179]
(N = 20). Scales above lateral line at midbody eight to
nine [9] (N = 25). Scales present along mid-dorsal
region of body to origin of midsaggital electroreceptive
filament. Origin of midsaggital electroreceptive fila-
ment located approximately at 64% of TL. Filament
extending posteriorly to vertical running through
posterior terminus of base of anal fin. Tail com-
pressed and short, ending in small, moderate,
fan-shaped caudal fin. Caudal-fin rays 15?17 [16]
(N = 21).
Coloration in alcohol: Overall coloration ranging from
tan to dark brown. Snout with distal portions pale
even in darkly pigmented specimens. Overall lightly
pigmented specimens with narrow, stripe of slightly
darker pigmentation extending anteriorly from orbit
for distance one-half to two-thirds length of snout.
Dark pigmentation on snout masked to varying
degrees in overall more darkly pigmented individuals.
Darker specimens with second band of dark pigmen-
tation running along ventral portion of snout. Two
bands of dark coloration separated by very narrow,
more lightly pigmented stripe along lateral surface of
snout. Dorsolateral region of dark pigmentation on
head forms lateral margin of narrow, somewhat
obscure and more lightly coloured mid-dorsal stripe.
Stripe somewhat laterally expanded over postocular
region and continuous posteriorly with more lightly
coloured mid-dorsal stripe on body that extends
varying degrees posteriorly, sometimes to origin of
electroreceptive filament. Lightly coloured stripes on
head and body more obvious in darker specimens.
Pectoral and anal fins in lightly pigmented specimens
hyaline. Pectoral fin in darker specimens dusky with
dark chromatophores concentrated over fin rays. Anal
fin in dark specimens slightly dusky, with dark chro-
matophores overlying fin rays but without any indi-
cation of distinct dark band along the distal margin.
Caudal fin with basal portions ranging from dusky to
distinctly dark and with distal region hyaline.
Distribution: Sternarchorhynchus stewarti is known
from the rivers of south-eastern Peru and eastern
Ecuador (Fig. 73).
Secondary sexual dimorphism: No sexual dimorphism
was apparent in the available samples of S. stewarti.
Etymology: The species name, stewarti, is in honour of
Donald Stewart, College of Environmental Science of
Forestry, State University of New York, who collected
the specimens that first brought this species to our
attention, and who has made many contributions to
our knowledge of the fishes of the western portions of
the Amazon basin.
Remarks: Examination of the specimens that served,
at least in part, as the basis for the citation of S.
curvirostris from the R?o Napo basin (Stewart et al.,
1987: 37) have shown them to be S. stewarti. Sterna-
rchorhynchus stewarti is very similar to S. cramptoni,
a species distributed in the Amazon basin from
Iquitos to the eastern portions of that drainage
system. Although the two species demonstrate
overlap in a number of meristic and morphometric
features, even the overall very dark individuals of S.
stewarti lack the distinct band of dark pigmentation
along the distal portions of the anal fin that is present
in all examined material of S. cramptoni including
overall lightly coloured individuals. These species also
differ to a large extent in the tail depth and distance
from the posterior nares to the snout.
Material examined
Holotype: ? PERU. Amazonas: R?o Mara?on, log riffle,
1.57 km east-north-east of Juan Velasco Santa Maria
de Nieva (4?50?S, 77?51?W), collected by N. K. Lujan,
D. C. Werneke, D. C. Taphorn, A. S. Flecker,
B. Rengifo, K. A. Capps, D. P. German, D. Osorio,
3.viii.2006; MUSM 30409 (182).
Paratypes: ? PERU. Amazonas: R?o Mara?on, log
riffle, 1.57 km east-north-east of Juan Velasco Santa
Maria de Nieva (4?50?S, 77?51?W), collected with holo-
type; MUSM 30410, 2 (105?132); AUM 46266, 2;
(164?180); UF 168165, 2 (96?126); CU 93464, 1 (74);
USNM 391571, 2 (155?242); ANSP 187150, 1 (170).
R?o Mara?on, log riffle, 1.57 km east-north-east of
Juan Velasco Santa Maria de Nieva (4?50?S, 77?51?W),
N. K. Lujan, D. C. Werneke, D. C. Taphorn, A. S.
Flecker, B. Rengifo, K. A. Capps, D. P. German, D.
Osorio, 8.viii.2006; AUM 46272, 4 (186?260); UF
168166, 3 (121?164), CU 93465, 3 (136?157); USNM
391572, 4 (133?155); ANSP 187151, 3 (116?183). R?o
Mara?on, 6.3 km north-east of Juan Velasco, Santa
Maria de Nieva (4?50?S, 77?51?W), N. K. Lujan, D. C.
Werneke, D. C. Taphorn, A. S. Flecker, B. Rengifo, D.
348 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Osorio, 4.viii.2006; AUM 46267, 1 (71); UF 168167,1
(95). R?o Mara?on, 1.5 km east-north-east of Juan
Velasco, Santa Maria de Nieva (4?50?S, 77?51?W), N.
K. Lujan, D. C. Werneke, D. C. Taphorn, A. S. Flecker,
B. Rengifo, D. Osorio, 4.viii.2006; AUM 46268, 1 (111);
UF 168168, 1 (128); CU 93466, 1 (202). R?o Nieva,
7.4 km south-south-west of Juan Velasco, Santa
Maria de Nieva (4?39?36?S, 77?53?24?W), N. K. Lujan,
D. C. Werneke, D. C. Taphorn, A. S. Flecker, B.
Rengifo, D. Osorio, 5.viii.2006; AUM 46269, 3 (63?
120); UF 168169, 2 (160?177); CU 93467, 2 (183?215);
USNM 391573, 2 (189?207); ANSP 187152, 2 (124?
200). R?o Mara?on, pongo above Borja, 35.5 km north-
east of Juan Velasco, Santa Maria de Nieva
(4?26?36?S, 77?34?54?W), N. K. Lujan, D. C. Werneke,
D. C. Taphorn, A. S. Flecker, B. Rengifo, D. Osorio,
6.viii.2006; AUM 46270, 1 (251); UF 168170, 1 (253);
CU 93468, 1 (226); AUM 46271, 1 (223). R?o Mara?on,
12 km north of Imacita (4?56?54?S, 78?20?24?W), N. K.
Lujan, D. C. Werneke, D. C. Taphorn, A. S. Flecker, B.
Rengifo, D. Osorio, 10.viii.2006; AUM 46273, 1 (110);
UF 168171, 1 (154); CU 93469, 1(138).
Nontype specimens: ? ECUADOR. Napo: R?o
Payamino, 23.3 km upstream from mouth in R?o
Napo, sandy beach on right bank (0?26?54?S,
77?06?12?W); FMNH 103364, 2 (214?222). R?o
Aguarico, few kilometres upstream from mouth of R?o
Eno (0?11?S, 76?30?W); FMNH 100616, 1 (154).
PERU. Amazonas: R?o Mara?on, vicinity of Santa
Maria de Nieva (Santa Maria de Nieva at 4?27?36?S,
77?34?53?W), collected by D. J. Stewart, 16.iv.1980;
LACM 41741?7, 8 (195?229). Loreto: R?o Mara?on,
along south side of R?o Mara?on, opposite Nauta
(4?30?39?S, 73?34?5?W); INHS 52735, 1 (94).
STERNARCHORHYNCHUS TAPHORNI SP. NOV.
(FIGS 73, 74; TABLE 13)
Diagnosis: Sternarchorhynchus taphorni is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
along the mid-dorsal region of the body, the presence
of a narrow, more lightly coloured mid-dorsal stripe
on the head and body extending posteriorly to the
vertical through the insertion of the pectoral fin at
least in smaller individuals, the dark anal fin, the
lateral line terminating at a point approximately
eight scales anterior of the base of the caudal fin, the
possession of eight premaxillary teeth, ten teeth in
total on the dentary, 14 branched pectoral-fin rays, 30
anterior unbranched anal-fin rays, 186 total anal-fin
rays, 12?13 premaxillary teeth, the length of the
anal-fin base (84.8% of LEA), the preanal distance
(11.0% of LEA), the prepectoral-fin distance (18.8% of
LEA), the pectoral-fin length (37.4?47.8% of HL), the
caudal length (6.8% of LEA), the head length (18.9%
of LEA), the snout length (51.1?62.2% of HL), the
head depth at the eye (31.8?46.8% of HL), the head
depth at the nape (55.7?62.3% of HL), the eye diam-
Figure 74. Sternarchorhynchus taphorni sp. nov., holotype, sexually dimorphic male demonstrating modifications of
dentary and dentary dentition, 310 mm total length, MUSM 6635; Peru, San Martin, R?o Huallaga.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 349
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
eter (5.7?6.0% of HL), the distance from the posterior
naris to the eye (35.9?52.4% of HL), the postocular
distance (43.5?46.4% of HL), the interocular width
(7.8?11.5% of HL), the length of the mouth (7.7?9.0%
of HL), the height of the branchial opening (11.6?
14.8% of HL), the tail depth (24.4% of caudal length),
and the caudal-fin length (50.2% of caudal length).
Description: Morphometric data for holotype and
nontype specimens in Table 13.
Lateral line extending to position about eight scales
anterior of hypural joint and absent on remainder of
tail and on caudal fin. Snout elongate, compressed
and notably curved ventrally distally. Posterior naris
closer to tip of snout than to anterior margin of eye.
Branchial opening restricted and situated slightly
anterior to vertical through pectoral-fin origin. Loca-
tion of anus and urogenital papilla apparently both
ontogenetically and sexually dimorphic based on
limited available sample. Anus and urogenital papilla
in small individual located along vertical running
three orbital diameters posterior of eye. Midsized
specimen with those structures located along vertical
through eye. Larger male with patch of enlarged
dentition on expanded dentary having anus and uro-
genital papilla more anteriorly positioned and located
along vertical two orbital diameters anterior of ante-
rior margin of orbit. Combined opening for anus and
urogenital papilla longitudinally ovoid.
Premaxilla of small size, somewhat rounded, with
eight teeth (N = 1). Dentary with two rows of irregu-
larly arranged teeth with total of ten teeth. Male
demonstrating sexual dimorphism in lower jaw with
anterior portion of jaw extending further anteriorly
than in females and juveniles and with dentary dis-
tinctly expanded laterally into dorsally bulbous struc-
ture rounded from dorsal view. Expanded portion of
dentary bearing series of enlarged, slightly posteri-
orly recurved teeth. Mouth terminal in juveniles and
females and somewhat anterodorsally directed in
male with expanded dentary. Position of rictus onto-
genetically slightly variable. Rictus located slightly
posterior to vertical through anterior naris in small-
est examined specimen (77 mm TL), approximately
at, or slightly anterior of, vertical running through
anterior naris in midsized specimen (216 mm TL) and
in male with large patch of dentition on enlarged
dentary (310 mm TL).
Branchiostegal rays five; with first to third rays
somewhat narrow and elongate and fourth and fifth
rays large and broad. Precaudal vertebrae 16 (13
anterior; three transitional; N = 1).
Pectoral-fin rays ii + 13?15 [ii + 15] (N = 3). Anal-fin
origin variable, located posterior to vertical running
through eye in small specimen (77 mm TL), along
vertical running through eye in midsized specimen
(216 mm TL), and anterior to vertical through eye in
largest specimen (male with large patch of enlarged
dentition on expanded dentary; 310 mm TL). Anterior
unbranched anal-fin rays 30 (N = 1). Total anal-fin
rays 186 (N = 1; largest specimen, only examined
individual without regenerated tail and damaged pos-
terior portion of anal fin). Scales above lateral line at
midbody 11?12 [11] (N = 3). Scales along mid-dorsal
region of body readily apparent on surface. Origin of
midsaggital electroreceptive filament located dis-
tinctly posterior of midlength of body. Filament in
large male (only specimen without regenerated tail
and damaged posterior portion of anal fin) terminat-
ing posteriorly two scales anterior of vertical running
through posterior terminus of base of anal fin. Tail
compressed and short, ending in small, somewhat
elongate caudal fin. Caudal-fin rays 14 (N = 1, largest
specimen; only individual without regenerated caudal
fin).
Coloration in alcohol: Overall ground coloration
brown to dark brown. Snout in smallest specimen
darker dorsolaterally and ventrally, with those areas
separated by very narrow, distinctly more lightly
coloured stripe. No such midlateral stripe on snout
present in other specimens, although dorsal region of
snout somewhat darker than lateral and ventral
portion of that portion of head in midsized individual.
Male with anteriorly expanded lower jaw bearing
patch of distinct enlarged teeth having head very
dark overall on lateral and ventral portions. Smallest
specimen (77 mm TL) with narrow, lightly coloured,
mid-dorsal stripe extending from snout along top of
head and mid-dorsal portion of body as far posteriorly
as vertical through posterior limit of pectoral fin.
Stripe apparent but less extensive in larger speci-
mens, reaching only to vertical about four orbital
diameters posterior of rear of eye in midsized speci-
men (216 mm TL) and only to vertical running
through anterior margin of eye in larger male
(310 mm TL).
Pectoral fin variably dark in all specimens and
particularly so in largest examined individual. Anal
fin dark in all individuals, with chromatophores over-
lying fin rays. Dark pigmentation particularly intense
along basal portion of fin in large male and forming
posteriorly attenuating dark band. Caudal fin dark
with distal portions less intensely pigmented.
Distribution: Examined specimens of S. taphorni
originated in the upper portions of the R?o Huallaga
and adjoining left bank tributaries of the R?o Ucayali
basin of eastern Peru (Fig. 73).
Secondary sexual dimorphism: The examined male of
S. taphorni has an anteriorly extended and laterally
enlarged anterior portion of the dentary with the
350 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
associated patch of enlarged teeth comparable to the
modifications of the jaw and teeth of some congeners.
The male also has the anus and urogenital papilla
more anteriorly positioned than in the examined
female and juvenile.
Etymology: The species name, taphorni, is in honour
of Donald Taphorn of the Universidad Nacional
Experimental de los Llanos Occidentales, who gener-
ously assisted the authors with this and other publi-
cations over the years and who has made many
contributions to our understanding of the South
American freshwater fish fauna.
Remarks: The two paratypes of S. taphorni examined
in this study agree with the holotype in examined
details and were collected in the same general region
in the Peruvian Amazon. The holotype originated,
however, within the R?o Huallaga system whereas the
two nontypes came from tributaries of the R?o
Ucayali. The common presence of a species in both
the R?o Huallaga system and left bank tributaries of
the R?o Ucayali was reported by Vari & Harold (2001:
172) for the characid Creagrutus ortegai. Some tribu-
taries of the R?o Ucayali approach portions of the R?o
Huallaga system (Isbr?cker & Nijssen, 1983: fig. 5)
and commonality of species across those portions of
the two river basins may be found to be a phenom-
enon of greater generality once the ichthyofauna of
that region is better explored ichthyologically.
Material examined
Holotype: ? PERU. Departamento de San Martin: R?o
Huallaga, Uchiza (approximately 8?29?59?S,
76?22?59?W); MUSM 6635 (310), collected by L. P.
Davilla, viii.1948.
Paratypes: ? PERU. Departamento de Hu?nuco: R?o
Llullapichis, 2 km upstream from mouth into R?o
Pachitea (9?37?S, 74?57?W), ROM 55531, 1 (216), col-
lected by E. Holm, B. Alvarado, H. Sisniegas. R?o
Llullapichis, 1.5 km west of Panguana Station
(9?37?S, 74?57?W), ROM 55530, 1 (77.3), collected by
E. Holm, B. Alvarado.
STERNARCHORHYNCHUS YEPEZI SP. NOV.
(FIGS 73, 75, 76; TABLE 14)
Diagnosis: Sternarchorhynchus yepezi is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, having sparse scales covered by skin along
the mid-dorsal portion of the body anterior to the
origin of the electroreceptive filament, the longitudi-
nally ovoid, but not distinctly horizontally elongate
combined opening for the anus and the urogenital
papilla, the consistently light overall coloration of the
head and body, the presence of very dark pigmenta-
tion in the region at the base of the anterior and
lateral margins of the enlarged teeth on the bulbous
dentary in mature males, the presence of a more
lightly coloured narrow band of mid-dorsal pigmenta-
tion on the head and mid-dorsal region of the body
extending posteriorly to the origin of the electrorecep-
tive filament and sometimes beyond that point, the
possession of seven teeth on the outer tooth row of the
dentary, 15 precaudal vertebrae, 182?188 total anal-
fin rays, the greatest body depth (11.3?13.2% of LEA),
the caudal length (8.1?8.4% of LEA), the pectoral-fin
length (43.1?44.2% of HL), the head depth at the eye
(30.5?40.0% of HL), the head depth at the nape (48.2?
Figure 75. Sternarchorhynchus yepezi sp. nov., holotype, sexually dimorphic male, 280 mm total length, MCNG
44286; Venezuela, Portuguesa, R?o Portuguesa.
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 351
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56.0% of HL), the snout length (58.7?61.7% of HL),
the eye diameter (4.1?4.8% of HL), the interocular
width (6.6?8.1% of HL), and the caudal-fin length
(33.2?38.8% of caudal length).
Description: Morphometric data for holotype and
paratypes in Table 14.
Lateral line extending to base of caudal fin but
absent on fin. Snout elongate, compressed and
Figure 76. Sternarchorhynchus yepezi sp. nov., immature specimen, 177 mm total length, ANSP 165222; Venezuela,
Apure, R?o Apure.
Table 14. Morphometric data for holotype (H), and paratypes of Sternarchorhynchus yepezi and Sternarchorhynchus
villasboasi
S. yepezi S. villasboasi
H Paratypes Mean H Paratypes Mean
Total length (mm) 282 108.2?177 (N = 2) ? 135 97.0?136 (N = 2) ?
Length to end of anal fin (mm) 260 98.9?173 (N = 2) ? 120 85.7?126 (N = 2) ?
Head length (mm) 46.46 22.5?34.0 (N = 2) ? 24.2 18.3?24.3 (N = 2) ?
Caudal length (mm) 21.09 8.37 (N = 1) ? 15.7 10.2 (N = 1) ?
Per cent of length to end of anal fin
Anal-fin base 91.1 81.9?87.8 (N = 2) 84.9 85.8 83.6?84.8 (N = 2) 84.2
Distance snout to anus 6.9 13.1?13.6 (N = 2) 13.3 9.4 9.5?11.6 (N = 2) 10.6
Preanal-fin distance 10.9 13.5?16.3 (N = 2) 14.9 12.8 12.5?14.7 (N = 2) 13.6
Prepectoral-fin distance 17.9 18.9?23.7 (N = 2) 21.3 19.9 19.4?21.1 (N = 2) 20.3
Greatest body depth 11.8 11.3?13.2 (N = 2) 12.2 12.3 12.9?11.9 (N = 2) 12.4
Head length 17.8 19.6?22.7 (N = 2) 21.2 20.2 19.4?21.3 (N = 2) 20.4
Caudal length 8.1 8.4 (N = 1) ? 13.1 11.9 (N = 1) ?
Per cent of head length
Anus to anal-fin insertion 21.8 10.4?17.8 (N = 2) 14.1 14.3 12.1?15.0 (N = 2) 13.6
Pectoral-fin length 43.1 43.2?44.2 (N = 2) 43.7 44.3 43.6?47.1 (N = 2) 45.4
Head depth at eye 40.0 30.5?33.2 (N = 2) 31.9 27.4 29.8?30.6 (N = 2) 30.2
Head depth at nape 56.0 48.2?54.0 (N = 2) 51.1 55.4 52.6?52.9 (N = 2) 50.7
Head width 26.1 22.0?26.3 (N = 2) 24.2 23.2 25.3?27.5 (N = 2) 26.4
Snout length 61.7 58.7?60.1 (N = 2) 59.4 53.3 53.6?56.1 (N = 2) 54.8
Posterior naris to snout 8.5 8.8?9.3 (N = 2) 9.0 9.0 8.9?9.6 (N = 2) 9.2
Posterior naris to eye 52.7 47.5?49.9 (N = 2) 48.7 41.5 39.7?45.4 (N = 2) 42.5
Mouth length 7.8 6.0?6.4 (N = 2) 6.2 7.0 5.8?7.3 (N = 2) 6.5
Internarial distance 3.2 2.7?3.7 (N = 2) 3.2 2.5 3.6?3.8 (N = 2) 3.7
Eye diameter 4.2 4.1?4.8 (N = 2) 4.4 5.7 5.0?5.9 (N = 2) 5.5
Interocular width 7.7 6.6?8.1 (N = 2) 7.4 6.9 9.4?13.1 (N = 2) 11.3
Postocular distance 40.5 43.8?46.2 (N = 2) 45.0 44.4 44.4?46.0 (N = 2) 45.2
Branchial opening 16.2 10.9?17.0 (N = 2) 13.9 13.7 15.3?15.4 (N = 2) 15.3
Per cent of caudal length
Tail depth 31.0 18.6 (N = 1) ? 14.2 12.2 (N = 1) ?
Caudal-fin length 33.2 38.8 (N = 1) ? 25 36.6 (N = 1) ?
Number of specimens indicated in parentheses.
352 C. D. DE SANTANA and R. P. VARI
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
notably curved ventrally distally. Posterior naris
located closer to tip of snout than to anterior margin
of eye. Branchial opening restricted and situated
slightly anterior to vertical through pectoral-fin
origin. Location of anus and urogenital papilla sexu-
ally dimorphic based on limited available sample.
Structures in small individual (112 mm TL) and
apparently mature female (177 mm TL) located along
vertical running two orbital diameters posterior of
eye. Males (280 mm TL) with definite patch of
enlarged dentition on dentary with anus and urogeni-
tal papilla more anteriorly positioned and located
along vertical running two orbital diameters anterior
of anterior margin of orbit. Combined opening for
anus and urogenital papillae longitudinally ovoid.
Premaxilla of small size, somewhat rounded, with
five to eight teeth (N = 3). Dentary in males trans-
versely expanded into dorsally bulbous structure
rounded from dorsal view and bearing series of
enlarged, posteriorly recurved teeth. Dentary in
single examined juvenile (112 mm TL) less elongate
and lacking such expansion. Form of dentary in
adults without expansion of anterior portion of
dentary unknown. Teeth in two rows, with total of 11
teeth, with seven teeth in outer row and four teeth on
inner row (N = 1). Mouth terminal in juveniles and
somewhat dorsally directed in males with expanded
dentaries. Location of rictus ontogenetically variable.
Rictus located slightly posterior to vertical through
anterior naris in smallest examined specimen
(112 mm TL), approximately at vertical through ante-
rior naris in midsized specimen (177 mm TL) and
clearly anterior of vertical running through that naris
in largest examined individual (280 mm TL).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15 (two anterior;
three transitional; N = 3).
Pectoral-fin rays ii + 13?14 [ii + 13] (N = 3). Position
of anal-fin origin either ontogenetically variable or
sexually dimorphic, but with underlying basis impos-
sible to ascertain from limited available sample.
Located slightly posterior of vertical through anterior
margin of opercle in smallest examined specimen
(112 mm TL), but positioned along vertical slightly
anterior of midpoint between anterior margin of
opercle and posterior margin of eye in largest exam-
ined specimen (male, 280 mm TL). Anterior
unbranched anal-fin rays 23?29 [29] (N = 3). Total
anal-fin rays 182?188 [187] (N = 3). Scales above
lateral line at midbody nine to 12 [11] (N = 3). Scales
along mid-dorsal region of body somewhat sparse and
not readily apparent on surface. Origin of midsaggital
electroreceptive filament located approximately at
65% of TL. Filament in specimens of all sizes extend-
ing to vertical through posterior terminus of base of
anal fin. Tail compressed and short, ending in very
small, somewhat elongate caudal fin. Caudal-fin rays
16?17 [17] (N = 2).
Coloration in alcohol: Overall ground coloration tan
to light greyish-tan. Snout ranging from nearly
hyaline in small and midsized specimens to slightly
grey in larger male with anteriorly expanded lower
jaw bearing patch of distinct enlarged teeth. Skin
around base of outer margin of patch of enlarged
teeth in that male much more darkly pigmented than
adjoining areas. Lower jaw without such dark pig-
mentation in other examined specimens (presumably
females and juveniles). Snout in all specimens with
distinct, narrow, anteriorly attenuating band of some-
what darker pigmentation extending from region
anterior of eye to anterior portion of snout. Dark
stripe nearly completely masked by ground coloration
in examined males. Dark pigmentation on snout
forms lateral border of narrow, more lightly coloured
mid-dorsal band on head that continues from tip of
snout to posterior margin of head. More lightly pig-
mented mid-dorsal band on head continuous posteri-
orly with lightly coloured mid-dorsal stripe extending
along body to origin of electroreceptive filament.
Pectoral fin hyaline in smallest examined specimen,
with some scattered dark pigmentation in somewhat
larger female and with fin rays overlain by series of
dark chromatophores in largest examined individual.
Anal fin hyaline in small specimen and female
paratype, with dark chromatophores overlying fin
rays in male (largest specimen examined). Caudal fin
hyaline or with faint dark pigmentation.
Distribution: The limited available samples of S.
yepezi all originated in the central portions of the R?o
Orinoco basin in Venezuela (Fig. 73). The range of the
species possibly extends to the Peruvian Amazon (see
discussion under Remarks; also under Possible addi-
tional undescribed species).
Secondary sexual dimorphism: Males of S. yepezi
share the anteriorly extended and laterally enlarged
anterior portion of the dentary and associated patch
of enlarged teeth present in some congeners. These
mature males also have the anus and urogenital
papilla more anteriorly positioned than do females
and juveniles, but with the degree of difference in the
position of those structures less pronounced than that
present in some congeners. The reduction is both a
consequence of the relatively more anterior position of
the anus and urogenital papilla in the immature
specimens and in the less distinctly advanced position
of those structures in the single examined male with
sexually dimorphic modifications of the lower jaw. It
is possible that the examination of more extensive
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 353
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
series of specimens will demonstrate a more pro-
nounced degree of sexual dimorphism in this feature.
Etymology: The species name, yepezi, is in honour of
Augustin Fern?ndez-Y?pez whose research on Ster-
narchorhynchus demonstrated that the diversity
within the genus was greater than then recognized.
Remarks: Two specimens from the Peruvian Amazon
examined during this study are very similar in many
details to S. yepezi or more likely represent yet
another undescribed species of the genus (see Possible
additional undescribed species, below).
Material examined
Holotype: ? VENEZUELA. Portuguesa: R?o Portu-
guesa, fort at Nueva Florida, Santa Rosal?a (approxi-
mately 8?57?N, 69?01?W), MCNG 44286 (280),
collected by O. Castillo and RNR students, 2001.
Paratypes: ? VENEZUELA. Apure: R?o Apure,
between mouth of R?o Portuguesa and San Fernando
de Apure (7?54?N, 67?32?W), ANSP 165222, 2 (112?
177), collected by S. A. Schaefer et al., 4.xi.1989.
Nontype specimens: ? VENEZUELA. Apure: R?o
Chirere, in Camachero, MBUCV-V-17394, 1 (320).
STERNARCHORHYNCHUS VILLASBOASI SP. NOV.
(FIGS 73, 77; TABLE 14)
Diagnosis: Sternarchorhynchus villasboasi is distin-
guished from congeners by the following combination
of characters: a short gape that terminates posteriorly
at, or slightly short of, the vertical through the ante-
rior nares, the presence of a definite series of scales
along the mid-dorsal region of the body, the lateral
line extending posteriorly to the base of the caudal
fin, the narrow, more lightly coloured mid-dorsal
stripe on the head that sometimes extends posteriorly
to the vertical through the insertion of the pectoral
fin, the slightly dusky anal fin, the possession of eight
to nine teeth on the premaxilla, eight to nine teeth in
the outer row of the dentary, 20?21 anterior
unbranched anal-fin rays, 160?166 total anal-fin rays,
the length of the base of the anal fin (83.6?85.8% of
LEA), the preanal distance (12.5?14.7% of LEA), the
caudal length (11.9?13.1% of LEA), the distance from
the anus to the anal-fin insertion (12.1?15.0% of HL),
the pectoral-fin length (43.6?47.1% of HL), the head
depth at the eye (27.4?30.6% of HL), the head depth
at the nape (52.6?55.4%), the mouth length (5.8?7.3%
of HL), the snout length (53.3.56.1% of HL), the
distance from the posterior naris to eye (39.7?45.4%
of HL), the postocular distance (44.4?46.0% of HL),
the height of the branchial opening (13.7?15.4% of
HL), the tail depth (12.2?14.2% of caudal length), and
the caudal-fin length (25.0?36.6% of caudal length).
Description: Morphometric data for examined speci-
mens in Table 14.
Lateral line extending posteriorly to base of caudal
fin but absent on fin. Snout elongate, compressed and
slightly curved ventrally distally. Mouth small and
terminal, with rictus located slightly anterior of ver-
tical running through anterior naris. Anus and uro-
genital papilla located ventral to head, with position
apparently ontogenetically variable in limited avail-
able sample. Structures located slightly posterior of
vertical running through eye in juvenile (97 mm TL)
and slightly anterior of vertical through eye in single
mature female (135 mm TL) and single mature male
(136 mm TL). Opening for anus and urogenital
papilla longitudinally ovoid both sexes.
Premaxilla with eight to nine teeth (N = 2) appar-
ent in whole specimens. Dentary with two tooth rows;
outer row with eight to nine teeth and inner row with
three teeth (N = 2).
Branchiostegal rays five; with first to third rays
narrow and elongate and fourth and fifth rays large
and broad. Precaudal vertebrae 15?16 (12 anterior;
three to four transitional; N = 3).
Pectoral-fin rays ii + 12?13 [ii + 12] (N = 3). Anal-fin
origin located anterior to vertical through margin of
opercle. Anterior unbranched anal-fin rays 20?22 [22]
(N = 3). Total anal-fin rays 160?166 [164] (N = 3).
Scales above lateral line at midbody ten to 12 [12]
(N = 3). Scales clearly present along mid-dorsal line to
Figure 77. Sternarchorhynchus villasboasi sp. nov., holotype, female, 135 mm total length, INPA 28361; Brazil,
Par?, Cachoeira de Kaituk?, Rio Xingu.
354 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
origin of midsaggital electroreceptive filament. Origin
of midsaggital electroreceptive filament located
approximately at 64% of TL. Filament extending pos-
teriorly to point located approximately two scales
anterior of vertical running through terminus of base
of anal fin in juvenile and single mature male, but
extending posteriorly one scale past terminus of base
of anal fin in single examined female. Tail compressed
and moderate, ending in small, elongate caudal fin.
Caudal-fin rays 16?17 [17] (N = 2).
Coloration in alcohol: Overall coloration of head and
body brown but darker dorsally. Snout dark overall
with stripe of distinctly darker pigmentation extend-
ing anteriorly from orbit to, or nearly to, tip of snout.
Ventral portion of snout dark. This dark coloration
along with dark pigmentation on dorsolateral region
of snout delimits distinctly more lightly pigmented
band running along lateral surface of snout. Mid-
dorsal region of head with narrow, lightly coloured
band extending from tip of snout to point approxi-
mately two-thirds of distance to vertical through eye.
Remainder of head and body dark along mid-dorsal
region. Pectoral distinctly dusky with rays covered
with small, dark chromatophores. Anal fin slightly
dusky with rays overlain by dark chromatophores.
Caudal fin dark with distal most margin hyaline.
Distribution: Sternarchorhynchus villasboasi is only
known from the type locality in the Rio Xingu at the
Cachoeira de Kaituk? (Fig. 73).
Secondary sexual dimorphism: The available sample
of S. villasboasi included a single mature male
(135 mm TL) and single mature female (136 mm TL)
as indicated by the examination of the gonads. No
sexual dimorphism was apparent between those two
individuals, but these specimens demonstrate that
the species matures at relatively small body sizes.
Ecology: Little information is available about the type
locality of S. villasboasi other than that it was a
rapids area in the Rio Xingu, Brazil (see also Campos-
da-Paz, 1999).
Etymology: The species name, villasboasi, is in
honour of Orlando Villa B?as, who was instrumental
in the designation of the Xingu National Park, in
recognition of his diverse endeavours to ameliorate
the impact of development projects on the indigenous
peoples of that region.
Material examined
Holotype: ? BRAZIL. Par?: Rio Xingu, Cachoeira de
Kaituk?, at Altamira (3?12?S, 52?12?W), L. Rapp
Py-Daniel and J. A. Zuanon, 9.x.1990; INPA 28361
(135, mature female).
Paratype: ? BRAZIL. Par?: Rio Xingu, Cachoeira de
Kaituk?, at Altamira (3?12?S, 52?12?W) L. Rapp
Py-Daniel and J. A. Zuanon, 1990; INPA 32084, 1
(136, mature male); INPA 3934, 1 (97).
POSSIBLE ADDITIONAL UNDESCRIBED SPECIES
The apparent tendency towards relatively small
scale endemicity in many species of Sternarchorhyn-
chus and the many regions within the known range
of the genus that are yet-to-be collected using
methods appropriate for securing samples of the
genus make it certain that Sternarchorhynchus is
undoubtedly more speciose, perhaps significantly
more speciose, than we document in this study. The
limited samples of Sternarchorhynchus from some
locations rendered it difficult to determine the
status of some specimens that we had at hand. In
some instances these samples may represent addi-
tional undescribed forms. The following summary
will hopefully encourage further collecting and
analysis of relevant population samples from the
cited areas in order to resolve the issue of the state
of these problematic specimens.
1. Two samples from the R?o Paragua basin
(MBUCV-V 20686; AMNH 91009). These are
similar to S. gnomus of the R?o Caron? basin
(which includes the R?o Paragua) in overall
appearance and morphometrics. The two samples
differ from S. gnomus in details of pigmentation
(primarily the presence of a narrow, lightly
coloured, mid-dorsal stripe on the head versus the
uniformly dark dorsal region of the head in S.
gnomus) and possibly osteology as evidenced by
differences apparent in radiographs. Additional
samples of Sternarchorhynchus from throughout
the R?o Caron? drainage system are necessary to
determine whether these differences are constant
across samples and, thus, indicative of an addi-
tional undescribed species.
2. One specimen that originated from the R?o Caura
(MCNG 34618), a right bank tributary of R?o
Orinoco, was cited as S. oxyrhynchus by
Rodr?guez-Olarte et al. (2003: 198) and is probably
the basis for the citation of that species for the
ichthyofauna of the R?o Caura basin by Lasso et al.
(2003: 239). The specimen is distinguished from all
other congeners in that basin other than S. oxy-
rhynchus by the uniformly dark mid-dorsal region
of the head and body (versus the presence of a
narrow, lightly coloured, mid-dorsal stripe on the
head and body in all other congeners in the R?o
Orinoco basin). The R?o Caura specimen differs,
however, from S. oxyrhynchus in its mouth form
(extends posteriorly only to a point distinctly short
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 355
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Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
of the vertical through the posterior nares versus
extending posteriorly beyond the vertical through
the posterior nares, respectively). Other features
further separate this specimen from all other con-
geners. Additional material is necessary to
adequately describe this probable undescribed
species.
3. Two specimens from the Peruvian Amazon that
were examined probably represent an undescribed
species of Sternarchorhynchus similar to S. yepezi
a R?o Orinoco endemic. The specimens share the
overall head and body form of S. yepezi along with
the distinctive dark pigmentation of the lower lip
in the area ventral to the external margin of the
patch of enlarged teeth on the bulbous dentary of
males. One of the individuals (UF 12354) origi-
nated from the aquarium trade at Iquitos, Peru,
which draws its material from a somewhat wide
area. This specimen is of relatively small body size
(167 mm TL), but nonetheless has a significantly
higher anal-fin ray count (197) than that in the
samples of S. yepezi examined in this study (182?
188). The second specimen (MCP 41639) is a large
male (261 mm TL) that bears a well-developed
patch of enlarged teeth on the expanded anterior
portion of the dentary. This specimen originated in
the Tef? region in the western Amazon and was
reported as Sternarchorhynchus n. sp. B by
Crampton & Albert (2006: 689) and Crampton
(2007: 289) on the basis of its EOD pattern. The
regenerated tail makes it impossible to secure
accurate counts of critical meristics and propor-
tional measurements, most importantly the anal-
fin ray count. In light of the differences and the
significant distance between the known range of S.
yepezi in the R?o Orinoco basin and sites of origin
of these two specimens in the western Amazon,
they probably represent an undescribed form. The
limited available sample of this form, the small
size of one individual, and the damage to a critical
region of the body in the other specimen, led us to
defer from proposing this form as a new
species.
Above and beyond the three highlighted examples,
photographs of specimens that originated from some
of the apparent geographical gaps within the range of
the genus but for which we did not have samples,
revealed populations that in some instances clearly
differ from the species of Sternarchorhynchus we rec-
ognize herein. This fact plus the large gaps in the
known distribution of the genus in the Amazon basin
make it likely that future studies will significantly
increase the known diversity of the species of Sterna-
rchorhynchus beyond the 32 species that we recognize
in this revision.
ACKNOWLEDGEMENTS
Research associated with this study was supported by
a Predoctoral Fellowship from the Smithsonian Insti-
tution in the Division of Fishes of the National
Museum of Natural History and by funding from the
Herbert R. and Evelyn Axelrod Chair in Systematic
Ichthyology in the Division of Fishes, National
Museum of Natural History of the Smithsonian Insti-
tution. We are indebted to the following individuals
and institutions for the loan and exchange of speci-
mens: Barbara Brown, Radford Arrindell, and Scott
Schaeffer (AMNH), John Lundberg, Mark Sabaj
Perez, and Kyle Luckenbill (ANSP), Jonathan Arm-
bruster and David Werneke (AUM), Ralf Britz and
Oliver Crimmen (BMNH), David Catania and Tomio
Iwamoto (CAS), John Friel (CU), Mary Anne Rogers
(FMNH), Javier Maldonado-Ocampo (IAVHP),
Michael Retzer (INHS), Luc?a Rapp Py-Daniel
(INPA), Georges Lenglet (IRScNB), Jeffrey Siegel and
Richard Fenney (LACM), Francisco Provenzano
(MBUCV), Donald Taphorn (MCNG), Luiz Malabarba
and Roberto Reis (MCP), Karsten Hartel (MCZ),
Sonia Fisch-Muller and Alain Merguin (MHNG),
Paulo Buckup (MNRJ), Hern?n Ortega (MUSM),
Osvaldo Oyakawa and M?rio de Pinna (MZUSP),
Erling Holm (ROM), Robert Robins (UF), Douglas
Nelson (UMMZ), Ronald Vonk (ZMA), Peter Bartsch
(ZMB), and William Crampton, University of Central
Florida. Peter Bartsch (ZMB) provided a photograph
and radiograph of the holotype of Sternarchus oxy-
rhynchus and meristic and morphometric data from
that specimen. Ernst Mikschi and Helmut Wellendorf
(NMW) arranged for radiographs of the two syntypes
of S. mormyrus and hospitality during a visit by the
second author. Mark Sabaj P?rez and Kyle Luckenbill
(ANSP) provided a photograph of one of the syntypes
of S. mormyrus. Most of the photographs in this paper
were prepared by T. Britt Griswold. The anatomical
drawings were prepared by Tamara L. Clark. Draw-
ings were labelled by Sandra J. Raredon (USNM) who
also prepared the distribution maps and provided
diverse invaluable technical assistance at the
National Museum of Natural History throughout the
course of the project.
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SUPPORTING INFORMATION
Additional Supporting Information may be found in the online version of this article:
Appendix S1. Cleared and stained material examined.
Please note: Wiley-Blackwell are not responsible for the content or functionality of any supporting materials
supplied by the authors. Any queries (other than missing material) should be directed to the corresponding
author for the article.
362 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
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PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 363
? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
APPENDIX 2
SYNAPOMORPHY LIST
The 24 numbered clades that appear in Figure 23 and
in the following list are present in all of the most
parsimonious trees recovered during the phylogenetic
analysis. A list of the character state transitions that
optimize unambiguously at the branch encompassing
each numbered clade in the strict consensus phylogeny
is provided, as are transitions that optimized as auta-
pomorphies for species. We limited the discussion to
characters pertinent to the hypothesis of a sister group
relationship of Platyurosternarchus and Sternarcho-
rhynchus and subunits of those genera. The scheme of
outgroup relationships shown in Figure 23 should not
be considered well supported because we did not
search for characters pertinent to the resolution of
relationships amongst those taxa nor necessarily
include published characters pertinent solely to the
question of relationships amongst the outgroup taxa.
A brief description of each synapomorphy is pro-
vided with more detailed information available under
the description of the character. Each synapomorphic
character state transition for Sternarchorhynchus or
a subunit of that genus is followed by information on
whether that state transition is a reversal within
Sternarchorhynchus, whether other clades within
Sternarchorhynchus have acquired that character
state independently, and whether additional charac-
ter state transitions in the character under discussion
occur within the clade defined by the synapomorphy.
Clade 1: Platyurosternarchus plus Sternarchorhyn-
chus (Tribe Sternarchorhynchini)
? Character 17, state 0?1; anguloarticular terminat-
ing posteriorly at, to posteriorly distinctly posterior
of, vertical through dorsal portion of joint between
angulo-articular and retroarticular and with dis-
tinct, posteriorly attenuating process extending
along anterior margin of retroarticular
? Character 42, state 0?1 (ACCTRAN); laterosen-
sory canal segment in vertical arm of preopercle in
form of two deeply anteriorly concave segments;
reversed to state 0 in Platyurosternarchus crypticus
and clade 10, reacquired in clade 20
? Character 61, state 0?1; very distinct constriction
of medial portion of fourth ceratobranchial
? Character 62, state 0?1; well-ossified fourth
infrapharyngobranchial with an overall triangular,
posteriorly widening form from dorsal view
? Character 63, state 0?1; cartilage along anterior
margin of first epibranchial expanded medially and
extending along all, or nearly all, of anterior
margin of cartilage at anterior of second
infrapharyngobranchial
? Character 68, state 0?1; absence of lateral
ethmoid
? Character 78, state 0?1 (DELTRAN); second
postcleithrum horizontally elongate; reversed in
clade 7
Clade 2: Platyurosternarchus
? Character 4, state 1?0; absence of teeth on pre-
maxilla; also present in Sternarchogiton labiatus in
outgroups
? Character 20, state 1?0; teeth attaching to exte-
rior surface of dentary
? Character 43, state 1?0 (ACCTRAN); dorsal
margin of opercle very slightly concave to distinctly
convex
? Character 52, state 0?1; anterior portion of urohyal
relatively wide and one-third or more of length of
main body of bone; also present in clade 7
? Character 79, state 1?0; intercalarium trans-
versely elongate
In a separate study focused on Platyurosternarchus,
de Santana & Vari (2009) identified three additional
synapomorphies for the species of the genus:
? the extension of the posterodorsal corner of the
maxilla into a posteriorly attenuating process
? the reduction of the posterior fontanel to a small
round opening bordered by the posteriormost por-
tions of the contralateral parietals and median
region of the anterior margin of the supraoccipital
? the distinct pigmentation pattern of dark ventro-
lateral and light dorsolateral pigmentation with a
patch of very dark pigmentation on the posterior
portion of the anal fin
Platyurosternarchus crypticus
? Character 26, state 0?1; presence of ascending
process of endopterygoid; also in clade 6
? Character 36, state 1?0; overall form of symplectic
bone relatively slender, with height of posterior-
most portion of symplectic approximately one-fifth
length of that bone; also occurs in clade 7
Character 42, state 1?0 (ACCTRAN); laterosensory
canal segment in vertical arm of preopercle in form of
two shallowly anteriorly concave segments; also
present in clade 10
Platyurosternarchus macrostoma
? Character 42, state 0?1 (DELTRAN); laterosen-
sory canal segment in vertical arm of preopercle in
form of two deeply anteriorly concave segments;
also present in clade 3, reversed in clade 10, and
reacquired in clade 20 and S. chaoi
? Character 45, state 0?1; association of posterodor-
sal corner of opercle and supracleithrum rounded
posterior extension of opercle extending over ven-
tralmost portion of supracleithrum; also occurs in
clade 6
364 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
? In their study of Platyurosternarchus de Santana &
Vari (2009) identified an additional synapomorphy
for P. macrostoma:
? The fusion of the extrascapular with the
neurocranium
Clade 3: Sternarchorhynchus
? Character 5, state 0?1; anterior portion of maxilla
with distinct anteriorly pointed process without
distinct anterior process
? Character 9, state 0?1; coronomeckelian bone
present as small rounded ossification in smaller
specimens, but absent in adults
? Character 10, state 0?1; Meckel?s cartilage well
developed in smaller individuals, but reduced onto-
genetically and highly reduced in adults
? Character 11, state 0?1; posterodorsal and poster-
oventral processes of dentary approximately of
same length
? Character 12, state 0?1; posteroventral process of
dentary very narrow and in form of elongate
narrow strut of bone
? Character 15, state 0?1; separation along dorsal
margin of anguloarticular between joint for articu-
lation with quadrate and anguloarticular?
retroarticular joint approximately about 4?4.5
times width of articular facet on anguloarticular
that forms joint
? Character 16, state 0?1; anterior portion of angu-
loarticular distinctly pointed with medial surface of
bone unelaborated
? Character 21, state 0?1; anterior portion of pala-
toquadrate cartilage poorly developed and reduced
to narrow, somewhat thread-like process
? Character 22, state 0?1; endopterygoid positioned
along medial surface of dentary and anguloarticu-
lar with dorsal margin of endopterygoid located
distinctly ventral of dorsal margins of dentary and
anguloarticular
? Character 23, state 0?1; anterior portion of endop-
terygoid very narrow and compressed transversely
and distinctly higher than wide
? Character 24, state 0?1; posterior portion of
endopterygoid reduced to very elongate, approxi-
mately horizontally aligned process extending
along, and tightly attached to, lateral surface of
quadrate and metapterygoid or fused to quadrate
in some species
? Character 28, state 0?1; dorsal portion of
quadrate without broad anterodorsal plate-like
process
? Character 35, state 0?1; posterior limit of
posteroventral portion of quadrate terminating
approximately at vertical through two-thirds of
length of metapterygoid or posterior of that
point
? Character 38, state 0?1; metapterygoid somewhat
to distinctly horizontally elongate and approxi-
mately quadrilateral
? Character 41, state 0?1 (ACCTRAN); preopercle
extending anteriorly to anterior of vertical through
ventral portion of joint between quadrate and
metapterygoid; reversed in clade 6, S. chaoi,
S. cramptoni, S. hagedornae, S. montanus, and
S. starksi
? Character 42, state 0?1 (DELTRAN); laterosen-
sory canal segment in vertical arm of preopercle in
form of two deeply anteriorly concave segments;
reversed in clade 10, and reacquired in clade 20
and S. chaoi
? Character 43, state 0?1 (DELTRAN); dorsal
margin of opercle distinctly concave
? Character 44, state 0?1; posterodorsal corner of
opercle extended in form of distinct process
? Character 46, state 0?1; presence of anteriormost
branchiostegal ray attaching to ventral margin of
anterior ceratohyal; reversed in S. caboclo
? Character 56, state 0?1; basihyal distinctly sepa-
rated from second basibranchial, with posterior of
basihyal extending posteriorly only to or proximate
to anterior region of ossified portion of first hypo-
branchial
? Character 64, state 0?1 (ACCTRAN); central
portion of myorhadoi with ventral elaboration;
transition to state 2 in S. chaoi
? Character 65, state 0?1 (ACCTRAN); position of
anus notably ontogenetically variable and shifting
anteriorly to location anterior to vertical through
eye in adults; reversed in S. curumim, S. gnomus,
S. oxyrhynchus, and clades 16, 22
? Character 67, state 0?1; distance from tip of
mesethmoid to vertical through posteriormost limit
of that bone equal to, or longer than, distance from
anteriormost point on frontal to anterior margin of
parietal distance
? Character 69, state 0?1; ventral portion of orbito-
sphenoid relatively narrow along anteroposterior
axis and not extending anteriorly along dorsal
margin of parasphenoid
? Character 72, state 0?1; anterior limit of anterior
fontanel falling short of anterior limit of
orbitosphenoid
? Character 75, state 0?1; presence of ossification
located in superficial tissues of body anterodorsal
to first postcleithrum; reversed in clades 8 with
reacquisition in S. chaoi, clade 18, and
S. mareikeae
? Character 88, state 0?1 (ACCTRAN); anal fin
hyaline to slightly dusky overall, and with distinct
band of dark pigmentation distally; reversed in
clade 7 and then reacquired independently in S.
montanus and clade 20
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 365
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Clade 4: Sternarchorhynchus goeldii and S.
oxyrhynchus
? Character 1, state 0?1; mouth short and posterior
terminus of gape extending posteriorly to beyond
vertical through posterior nares
? Character 6, state 0?1; anterior portion of maxilla
reduced and only slightly wider than main portion
of bone
? Character 8, state 0?1; fleshy pad at anterior of
dentary well developed, dorsally directed, and over-
lapping tip of snout in closed mouth
? Character 25, state 0?1; quadrate and endoptery-
goid fused
? Character 30, state 0?1; posterolateral portion of
quadrate with lateral expansion into rounded ridge
terminating posteriorly in articular facet
? Character 32, state 1?0; anterior portion of sym-
plectic fitting into notch or pocket along poster-
oventral margin of quadrate located distinctly
posterior of ventral limit of joint between quadrate
and metapterygoid; also present in S. curvirostris
? Character 37, state 0?1; anterodorsally directly
process on dorsal margin of symplectic present;
evolved independently in S. curumim and clade 14,
reversed in clade 21
? Character 39, state 0?1; lateral surface of dorsal
portion of metapterygoid with distinct rounded
lateral ridge terminating anteriorly in well-
developed articular surface
? Character 41, state 0?1 (DELTRAN); anterior
extent of preopercle extending to location anterior
of vertical through ventral portion of joint between
quadrate and metapterygoid; also present in clade
7, reversed in S. chaoi, S. cramptoni, S. hagedor-
nae, and S. montanus
? Character 49, state 0?1; anterodorsal margin of
third branchiostegal ray with distinct angular
process
? Character 76, state 0?1 (DELTRAN); ossification
located anterodorsal to first postcleithrum elon-
gate; also occurs in clade 6, S. britskii, and S.
curvirostris
? Character 88, state 0?1 (DELTRAN); fin hyaline
to slightly dusky overall, and with distinct band of
dark pigmentation distally; acquired independently
in clades 6, 20, and S. montanus
Sternarchorhynchus goeldii
? Character 64, state 1?0 (ACCTRAN); central
portion of myorhadoi without ventral or dorsal
elaborations; also occurs in Platyurosternarchus
? Character 65, state 0?1 (DELTRAN); position of
anus notably ontogenetically variable and shifting
anteriorly to location anterior to vertical through
eye in adults; also evolved independently in clade 5
with subsequent reversals in S. curumim, S.
gnomus, clade 16, and clade 22
Sternarchorhynchus oxyrhynchus
? Character 64, state 0?1 (DELTRAN); central
portion of myorhadoi with ventral elaboration; also
occurs in clade 5
? Character 65, state 1?0 (ACCTRAN); position of
anus relatively invariant in juveniles and adults
with anus situated posterior to vertical through eye
in adults; also occurs independently in S. gnomus,
clade 16, and clade 22
Clade 5: Sternarchorhynchus axelrodi, S. britskii,
S. caboclo, S. chaoi, S. cramptoni, S. curumim,
S. curvirostris, S. hagedornae, S. higuchii, S. inpai,
S. jaimei, S. gnomus, S. mareikeae, S. mendesi,
S. mesensis, S. montanus, S. mormyrus, S. retzeri,
S. roseni, S. severii, S. starksi, and S. stewarti
? Character 2, state 0?1; skin of upper lip with
distinct fold; also occurs in Sternarchella orthos in
outgroups
? Character 7, state 0?1; ventral margin of maxilla
with distinct concavity
? Character 18, state 0?1; posterior limit of dentary
located along vertical through vertical component
of orbitosphenoid
? Character 54, state 0?1 (ACCTRAN); basihyal
with lateral processes; reversed in S. britskii,
S. jaimei, and clade 24 with reacquisition in
S. mendesi
? Character 54, state 0?1 (DELTRAN as an exclu-
sive synapomorphy); basihyal with lateral
processes; independently reversed in S. britskii,
S. higuchii, S. jaimei, and S. roseni
? Character 59, state 0?1; anterior portion of second
hypobranchial with distinct anterior extension
from main body
? Character 64, state 0?1 (DELTRAN); central
portion of myorhadoi with ventral elaboration; also
present in S. oxyrhynchus; modified to state 2 in
S. chaoi
? Character 65, state 0?1 (DELTRAN); position of
anus notably ontogenetically variable and shifting
anteriorly to location anterior to vertical through
eye in adults; reversed independently in
S. curumim, S. gnomus, clade 16, and clade 22
? Character 66, state 0?1; presence of scythe-shaped
process along lateral margin of ventral ethmoid
? Character 86, state 0?1; presence of narrow,
lightly coloured stripe on lateral surface of snout;
reversed independently in clade 16 and S. roseni
Clade 6: Sternarchorhynchus axelrodi and S.
mormyrus
366 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
? Character 6, state 0?2; anterior portion of maxilla
distinctly expanded into somewhat square plate
with irregular margins
? Character 26, state 0?1 (ACCTRAN); presence of
ascending process of endopterygoid; also present in
P. crypticus in outgroup
? Character 31, state 0?1; posteroventral margin of
main body of quadrate that receives anterior tip of
symplectic with notch very small or absent and
enclosed laterally and medially by vertical sheet of
bone
? Character 41, state 1?0 (ACCTRAN); preopercle
terminating anteriorly variably posterior of vertical
through ventral portion of joint between quadrate
and metapterygoid; also present independently in
S. chaoi, S. cramptoni, S. hagedornae, S. monta-
nus, and S. starksi
? Character 45, state 0?1; rounded posterior exten-
sion of opercle extending over ventralmost portion
of supracleithrum; also present in P. macrostoma
? Character 58, state 0?1(ACCTRAN); second basi-
branchial with lateral margins running approxi-
mately in parallel; occurs independently in
S. severii
? Character 70, state 0?1; posterior margin of
orbitosphenoid concave and contacting pterosphe-
noid only at dorsal and ventral limits of areas of
contact of orbitosphenoid and pterosphenoid
? Character 71, state 0?1; anterior margin of
pterosphenoid concave and contacting orbitosphe-
noid only at dorsal and ventral limits of areas of
contact of pterosphenoid and orbitosphenoid
? Character 76, state 0?1 (DELTRAN); ossification
located anterodorsal to first postcleithrum elon-
gate; also occurs independently in clade 4, S. brit-
skii, and S. curvirostris
? Character 88, state 0?1 (DELTRAN); anal fin
hyaline to slightly dusky overall with distinct band
of dark pigmentation distally; also occurs indepen-
dently in clade 4, clade 22, and S. montanus within
Sternarchorhynchus
Clade 7: Sternarchorhynchus britskii, S. caboclo, S.
chaoi, S. cramptoni, S. curumim, S. curvirostris, S.
hagedornae, S. higuchii, S. inpai, S. jaimei, S.
gnomus, S. mareikeae, S. mendesi, S. mesensis, S.
montanus, S. retzeri, S. roseni, S. severii, S. starksi,
and S. stewarti
? Character 3, state 0?1; premaxilla compact with
longitudinal length approximately equal to trans-
verse width
? Character 29, state 0?1; dorsal margin of quadrate
concave
? Character 36, state 1?0; Symplectic relatively
slender, with height of posteriormost portion of
bone approximately one-fifth length of bone.
? Character 40, state 0?1; tip of posteroventral
process of quadrate fitting into variably developed
notch along dorsal margin of preopercle
? Character 41, state 0?1 (DELTRAN); preopercle
extending anteriorly to location anterior of vertical
through ventral portion of joint between quadrate
and metapterygoid; also present in clade 4;
reversed to state 0 in S. chaoi, S. cramptoni, S.
hagedornae, S. montanus, and S. starksi
? Character 52, state 0?1; anterior portion of urohyal
relatively wide and one-third or more of length of
main body of bone; also occurs independently in
clade 2, and in Sternarchella orthos in outgroups
? Character 76, state 1?0 (ACCTRAN); ossification
located anterodorsal to first postcleithrum rhomboid
or ovoid; reversed to state 1 independently in S.
britskii and S. curvirostris
? Character 78, state 1?0; second postcleithrum
rounded or slightly longitudinally ovoid
? Character 82, state 1?0; scales present along mid-
dorsal region of body anterior to origin of electrore-
ceptive filament; reversed in clade 22
? Character 83, state 0?1 (ACCTRAN); scales absent
along mid-dorsal region only to region approxi-
mately at vertical through posterior margin of pec-
toral fin
? Character 88, state 1?0 (ACCTRAN); anal fin
hyaline to slightly dusky overall, but lacking dis-
tinct band of dark pigmentation distally; also
present in P. crypticus and P. macrostoma; reversed
in clade 20
Clade 8: Sternarchorhynchus caboclo and S. curumim
? Character 75, state 1?0; absence of ossification
located in superficial tissues of body anterodorsal
to first postcleithrum; also occurs in clade 18,
reversed to state 1 in S. chaoi
Sternarchorhynchus caboclo
? Character 13, state 0?1; posteroventral process of
dentary not reaching margin of posteroventral
process of anguloarticular; reversed in clade 15;
also occurs independently in S. britskii, S. gnomus,
S. higuchii, S. mareikeae, and S. stewarti
? Character 33, state 0?1; absence of lateral closure
of notch along posteroventral margin of quadrate
that receives symplectic; also present in clade
19 with reversal in clade 24 and reacquisition in
S. roseni
? Character 46, state 1?0; absence of anteriormost
branchiostegal ray attaching to ventral margin of
anterior ceratohyal
? Character 51, state 0?1; dorsal margin of proxi-
mate portion of anterior branchiostegal ray attach-
ing to lateral surface of the anterior ceratohyal
concave with angled margins
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 367
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
? Character 60, state 0?1; medial portion of second
hypobranchial in adults without distinct medial
process and with contralateral second hypobranchi-
als separated by second basibranchial; also present
in S. higuchii
? Character 74, state 0?1; slender anteroventral
process of coracoid, terminating anteriorly dis-
tinctly short of medial surface of cleithrum and
with gap filled by distinct cartilage mass; also
present in S. britskii
Clade 9: Sternarchorhynchus britskii, S. chaoi, S.
cramptoni, S. curvirostris, S. hagedornae, S. higuchii,
S. inpai, S. jaimei, S. gnomus, S. mareikeae, S.
mendesi, S. mesensis, S. montanus, S. retzeri, S.
roseni, S. severii, S. starksi, and S. stewarti
? Character 27, state 0?1 (ACCTRAN); pterygocra-
nial ligament attaching to both endopterygoid and
quadrate; reversed in S. curvirostris and clade 21
with reacquisition in S. jaimei
? Character 27, state 0?1 (DELTRAN); pterygocra-
nial ligament attaching to both endopterygoid and
quadrate; reversed in S. curvirostris, S. chaoi, and
clade 23
? Character 85, state 0?1; mid-dorsal region of head
with narrow, mid-dorsal, lightly coloured stripe
Sternarchorhynchus severii
? Character 58, state 0?1; second basibranchial with
lateral margins running approximately in parallel;
also occurs in clade 15 with reversal in clade 24
Clade 10: Sternarchorhynchus britskii, S. chaoi, S.
cramptoni, S. curvirostris, S. hagedornae, S. higuchii,
S. inpai, S. jaimei, S. gnomus, S. mareikeae,
S. mendesi, S. mesensis, S. montanus, S. retzeri,
S. roseni, S. starksi, and S. stewarti
? Character 42, state 1?0; laterosensory canal
segment in vertical arm of preopercle in form of
two shallowly anteriorly concave segments;
reversed independently in clade 20 and S. chaoi
Clade 11: Sternarchorhynchus inpai and S. montanus
? Character 51, state 0?1; form of dorsal margin of
proximate portion of anterior branchiostegal ray
attaching to lateral surface of the anterior cerato-
hyal dorsally pointed or rounded
Sternarchorhynchus inpai
? Character 48, state 0?1; first branchiostegal ray
approximately one-third length of second bran-
chiostegal ray
? Character 77, state 1?2; three postcleithra
present; also occurs independently in S. curviros-
tris and clade 23
Sternarchorhynchus montanus
? Character 41, state 1?0; preopercle terminating
anteriorly variably posterior of vertical through
ventral portion of joint between quadrate and
metapterygoid; also occurs independently in S.
axelrodi, S. chaoi, S. cramptoni, S. hagedornae, S.
mormyrus, and S. starksi
? Character 53, state 0?1; anterior margin of
urohyal with distinct medial notch; also occurs in
clade 17 with independent reversals in S. retzeri
and S. mendesi
? Character 88, state 0?1; anal fin hyaline to
slightly dusky overall with distinct band of dark
pigmentation distally; also occurs independently in
clade 20
Clade 12: Sternarchorhynchus britskii, S. chaoi, S.
cramptoni, S. curvirostris, S. hagedornae, S. higuchii,
S. jaimei, S. gnomus, S. mareikeae, S. mendesi,
S. mesensis, S. retzeri, S. roseni, S. starksi, and
S. stewarti
? Character 13, state 0?1; posteroventral process of
dentary not reaching margin of posteroventral
process of anguloarticular; reversed in clade
15 with state 1 reacquired independently in
S. higuchii and S. stewarti
Sternarchorhynchus britskii
? Character 54, state 1?0; basihyal without lateral
processes; also occurs independently in S. jaimei
and clade 24 with reversal in S. mendesi
? Character 74, state 0?1; slender anteroventral
process of coracoid terminating anteriorly dis-
tinctly short of medial surface of cleithrum and
with gap filled by distinct cartilage mass; also
occurs independently in S. caboclo
? Character 76, state 0?1; ossification located
anterodorsal to first postcleithrum elongate; also
present independently in S. curvirostris, and clades
3 and 5
Clade 13: Sternarchorhynchus chaoi, S. cramptoni,
S. curvirostris, S. gnomus, S. hagedornae, S. higuchii,
S. jaimei, S. mareikeae, S. mendesi, S. mesensis,
S. retzeri, S. roseni, S. starksi, and S. stewarti
? Character 34, state 0?1; presence of overlap lat-
erally of anteroventral corner of metapterygoid by
bony process of quadrate; reversed in clade 18 with
reacquisition in S. higuchii
Sternarchorhynchus gnomus
? Character 65, state 1?0; anus position relatively
invariant in juveniles and adults with anus situ-
ated posterior to vertical through eye in adults;
also occurs in clades 16 and 22
368 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Clade 14: Sternarchorhynchus chaoi, S. cramptoni,
S. curvirostris, S. hagedornae, S. higuchii, S. jaimei,
S. mareikeae, S. mendesi, S. mesensis, S. retzeri,
S. roseni, S. starksi, and S. stewarti
? Character 37, state 0?1; presence of anterodor-
sally directed process on dorsal margin of symplec-
tic; reversed in clade 21
Sternarchorhynchus mareikeae
? Character 75, state 1?0; absence of ossification
located in superficial tissues of body anterodorsal
to first postcleithrum; also occurs independently in
clade 18 with subsequent reversal in S. chaoi
Clade 15: Sternarchorhynchus chaoi, S. cramptoni, S.
curvirostris, S. hagedornae, S. higuchii, S. jaimei, S.
mendesi, S. mesensis, S. retzeri, S. roseni, S. starksi,
and S. stewarti
? Character 13, state 1?0; posteroventral process of
dentary reaching margin of posteroventral process
of anguloarticular; reversed independently in S.
higuchii and S. stewarti
? Character 58, state 0?1; second basibranchial with
lateral margins running approximately in parallel;
reversed in clade 24
Clade 16: Sternarchorhynchus curvirostris and
S. starksi
? Character 65, state 1?0; position of anus relatively
invariant in juveniles and adults with anus situ-
ated posterior to vertical through eye in adults;
also present independently in clade 22
? Character 86, state 1?0; lateral surface of snout
with pigmentation comparable to that of adjoining
regions or with irregular marbling; further present
in S. roseni
Sternarchorhynchus curvirostris
? Character 27, state 1?0; pterygocranial
ligament attachment limited to dorsal surface of
endopterygoid; also reversed independently in S.
jaimei
? Character 32, state 1?0; anterior portion of sym-
plectic fitting into notch or bony pocket along pos-
teroventral margin of quadrate located anterior of
ventral limit of joint between quadrate and metap-
terygoid; also present in clade 4
? Character 76, state 0?1; ossification located
anterodorsal to first postcleithrum elongate; also
occurs independently in S. britskii
? Character 77, state 1?2; three postcleithra
present; also occurs independently in S. inpai and
clade 23
? Character 87, state 0?1; anal fin hyaline to
slightly dusky overall, and with distinct band of
dark pigmentation basally
Sternarchorhynchus starksi
? Character 41, state 1?0; preopercle terminating
anteriorly variably posterior of vertical through
ventral portion of joint between quadrate and
metapterygoid; also occurs independently in clade
6, S. chaoi, S. cramptoni, S. hagedornae, and
S. montanus
? Character 79, state 0?2; intercalarium medially
tapering and triangular overall; also present in
S. mesensis
Clade 17: Sternarchorhynchus chaoi, S. cramptoni,
S. hagedornae, S. higuchii, S. jaimei, S. mendesi,
S. mesensis, S. retzeri, S. roseni, and S. stewarti
? Character 53, state 0?1; anterior margin of
urohyal, with distinct medial notch; also occurs in
S. montanus; reversed in S. retzeri and further in
S. mendesi
Sternarchorhynchus hagedornae
? Character 41, state 1?0; preopercle terminating
anteriorly variably posterior of vertical through
ventral portion of joint between quadrate and
metapterygoid; also occurs independently in S.
chaoi, S. cramptoni, S. montanus, and S. starksi
? Character 84, state 0?1; scales sparse and covered
to different degrees by skin; also occurs in clade 24
Clade 18: Sternarchorhynchus chaoi, S. cramptoni, S.
higuchii, S. jaimei, S. mendesi, S. mesensis, S. retzeri,
S. roseni, and S. stewarti
? Character 34, state 1?0; absence of overlap later-
ally of anteroventral corner of metapterygoid by
bony process of quadrate
? Character 75, state 1?0; absence of ossification
located in superficial tissues of body anterodorsal
to first postcleithrum; character reversed in
S. chaoi: state 0 also occurs in S. mareikeae
Sternarchorhynchus stewarti
? Character 13, state 0?1; posteroventral process of
dentary not reaching margin of posteroventral
process of anguloarticular; also occurs indepen-
dently in S. britskii, S. caboclo, S. gnomus, S.
higuchii, and S. mareikeae
Clade 19: Sternarchorhynchus chaoi, S. cramptoni, S.
higuchii, S. jaimei, S. mendesi, S. mesensis, S. roseni,
and S. retzeri
? Character 33, state 0?1; absence of lateral closure
of notch along posteroventral margin of quadrate
that receives symplectic; reversed in clade 24 and
reacquired in S. roseni; state 1 also present inde-
pendently in S. caboclo
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 369
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
Clade 20: Sternarchorhynchus cramptoni and
S. retzeri
? Character 42, state 0?1; laterosensory canal
segment in vertical arm of preopercle in form of
two deeply anteriorly concave segments; also
present independently in clades 4, 6, S. caboclo,
S. chaoi, S. curumim, and S. severii
? Character 88, state 0?1; anal fin hyaline to
slightly dusky overall, and with distinct band of
dark pigmentation distally; also occurs in clades 4,
6, and S. montanus
Sternarchorhynchus cramptoni
? Character 41, state 1?0; preopercle terminating
anteriorly variably posterior of vertical through
ventral portion of joint between quadrate and
metapterygoid; also present independently in clade
6, S. chaoi, S. cramptoni, S. hagedornae, S. mon-
tanus, and S. starksi
Sternarchorhynchus retzeri
? Character 53, state 1?0; anterior margin of
urohyal straight or slightly irregular, but without
distinct medial notch; also present in S. mendesi
Clade 21: Sternarchorhynchus chaoi, S. higuchii,
S. jaimei, S. mendesi, S. mesensis, and S. roseni
? Character 27, state 1?0 (ACCTRAN); pterygocra-
nial ligament attachment limited to dorsal surface
of endopterygoid; reversed to state 1 in S. jaimei;
state 0 also occurs independently in clade 4,
S. caboclo, S. curvirostris, and S. mormyrus
? Character 37, state 1?0; absence of anterodorsally
directed process on dorsal margin of symplectic
Clade 22: Sternarchorhynchus chaoi and S. jaimei
? Character 65, state 1?0; position of anus relatively
invariant in juveniles and adults with anus situ-
ated posterior to vertical through eye in adults;
also present independently in clade 16
? Character 82, state 1?0; scales reduced to some
extent and sometimes largely absent along mid-
dorsal region of body anterior to origin of electrore-
ceptive filament
? Character 83, state 0?1 (DELTRAN); scales
absent along mid-dorsal region only to region
approximately at vertical through posterior margin
of pectoral fin
Sternarchorhynchus chaoi
? Character 27, state 1?0 (DELTRAN); pterygocra-
nial ligament attachment limited to dorsal surface
of endopterygoid; also occurs independently
in clade 4, S. caboclo, S. curvirostris, and
S. mormyrus
? Character 41, state 1?0; preopercle terminating
anteriorly variably posterior of vertical through
ventral portion of joint between quadrate and
metapterygoid; also present independently in S.
cramptoni, S. hagedornae, S. montanus, S.
mormyrus, and S. starksi
? Character 42, state 0?1; laterosensory canal
segment in vertical arm of preopercle in form of
two deeply anteriorly concave segments; also
present independently in clades 4, 6, and 20
? Character 64, state 1?2; central portion of myo-
rhadoi with ventral and dorsal elaborations
? Character 75, state 0?1; presence of ossification
located in superficial tissues of body anterodorsal
to first postcleithrum; also occurs in clades, 4, 6, S.
britskii, S. curvirostris, S. gnomus, S. hagedornae,
S. inpai, S. montanus, S. severii, and S. starksi
Sternarchorhynchus jaimei
? Character 27, state 0?1 (ACCTRAN); pterygocra-
nial ligament involving both endopterygoid and
quadrate; also occurs in clade 9, with reversal in S.
curvirostris and clade 20
? Character 54, state 1?0; basihyal without lateral
processes; also present independently in S. britskii
and clades 4 and 24 with reversal in S. mendesi
Clade 23: Sternarchorhynchus higuchii, S. mendesi,
S. mesensis, and S. roseni
? Character 27, state 1?0 (DELTRAN); pterygocra-
nial ligament attachment limited to dorsal surface
of endopterygoid; also occurs independently
in clade 4, S. caboclo, S. chaoi, S. curvirostris, and
S. mormyrus
? Character 77, state 1?2; three postcleithra
present; also occurs independently in S. inpai and
S. curvirostris
Sternarchorhynchus mesensis
? Character 79, state 0?2; intercalarium medially
tapering and triangular overall; also present in S.
starksi
? Character 80, state 0?1; tripus not distinctly nar-
rowing distally and relatively wide for distal half of
bone
Clade 24: Sternarchorhynchus higuchii, S. mendesi,
and S. roseni
? Character 33, state 1?0 (ACCTRAN); presence of
lateral closure of notch along posteroventral
margin of quadrate that receives symplectic;
reversed in S. roseni
? Character 54, state 1?0; basihyal without lateral
processes; reversed in S. mendesi; state 0 also
present independently in S. britskii and S.
jaimei
370 C. D. DE SANTANA and R. P. VARI
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371
? Character 58, state 1?0; second basibranchial with
midlength constriction
? Character 84, state 0?1; scales sparse and covered
to different degrees by skin; also occurs in S.
hagedornae
Two equally parsimonious trees were found in the
analyses for the relationships amongst S. higuchii, S.
mendesi, and S. roseni. These alternatives resulted in
an unresolved trichotomy at this level. Details on the
characters that supported each alternative are as
follows:
Sternarchorhynchus roseni as sister group to clade
formed by S. higuchii and S. mendesi
? Character 33, state 1?0 (ACCTRAN and
DELTRAN); presence of lateral closure of notch
along posteroventral margin of quadrate that
receives symplectic.
Sternarchorhynchus mendesi as sister group to clade
formed by S. higuchii and S. roseni
? Character 54, state 1?0; basihyal without lateral
processes; state 0 also present independently in S.
britskii and S. jaimei
Autapomorphies for the three species in this unre-
solved tricotomy are:
Sternarchorhynchus higuchii
? Character 13, state 0?1; posteroventral process of
dentary not reaching margin of posteroventral
process of anguloarticular; also occurs indepen-
dently in S. caboclo and S. stewarti
? Character 33, state 1?0 (DELTRAN); presence of
lateral closure of notch along posteroventral
margin of quadrate that receives symplectic; also
present in S. mendesi
? Character 34, state 0?1; presence of overlap lat-
erally of anteroventral corner of metapterygoid by
bony process of quadrate; also occurs indepen-
dently in S. gnomus and S. higuchii
? Character 54, state 1?0 (DELTRAN); basihyal
without lateral processes; also present indepen-
dently in S. jaimei and S. roseni
? Character 60, state 0?1; medial portion of second
hypobranchial in adults without distinct medial
process and with contralateral second hypobranchi-
als separated by second basibranchial; also occurs
in S. caboclo
? Character 77, state 0?1; two postcleithra present
Sternarchorhynchus mendesi
? Character 33, state 1?0 (DELTRAN); presence of
lateral closure of notch along posteroventral
margin of quadrate that receives symplectic; also
present independently in S. higuchii
? Character 53, state 1?0; anterior margin of
urohyal, straight or slightly irregular, but without
distinct medial notch; also present independently
in S. retzeri
? Character 54, state 0?1 (ACCTRAN); basihyal
with lateral processes; also occurs in clade 5
Sternarchorhynchus roseni
? Character 33, state 0?1 (ACCTRAN); absence of
lateral closure of notch along posteroventral
margin of quadrate that receives symplectic; also
present in S. caboclo and clade 19
? Character 54, state 1?0 (DELTRAN); basihyal
without lateral processes; also present indepen-
dently in S. britskii, S. higuchii, and S. jaimei
? Character 86, state 1?0; lateral surface of snout
with pigmentation comparable to that of adjoining
regions or with irregular marbling; also occurs in
clade 16
PHYLOGENY AND REVISION OF STERNARCHORHYNCHUS 371
No claim to original US government works.
Journal compilation ? 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 223?371