17 October 1986 
PROC. BIOL. SOC. WASH. 
99(3), 1986, pp. 444-451 
A NEW SCALE-WORM COMMENSAL WITH DEEP-SEA 
MUSSELS IN THE SEEP-SITES AT THE FLORIDA 
ESCARPMENT IN THE EASTERN GULF OF MEXICO 
(POLYCHAETA: POLYNOIDAE: BRANCHIPOLYNOINAE) 
Marian H. Pettibone 
Abstract.?Some polynoid polychaetes found living commensally in mantle 
cavities of deep-sea mussels at the seep-sites near the Florida Escarpment, are 
described as a new species of Branchipolynoe, B. seepensis. They show some 
differences from the previously described B. symmytilida, commensal with 
deep-sea mussels in the Galapagos hydrothermal vents. 
Among the abundant biological com- 
munities recently discovered in the abyssal 
eastern Gulf of Mexico near hypersaline 
seep-sites were large dense mats of mussels 
(Florida Escarpment Cruise Participants 
1984, Pauli et al. 1984, Turner and Lutz 
1984, Denoux et al. 1985, Hecker 1985). 
They were collected in March 1984 during 
four dives of the submersible Alvin in 3266- 
3270 meters (26?02'N, M?55'W). The mus- 
sels were found in dark iron-sulfide sedi- 
ments at near-ambient temperatures in an 
area where dense hypersaline fluids seep out 
onto the sea floor. The communities were 
similar in many respects to the prolific com- 
munities found around the Galapagos hy- 
drothermal vents and elsewhere in the Pa- 
cific. 
Some polynoid polychaetes were found 
living commensally in the mantle cavities 
of these mussels. Six specimens were given 
to me for study by Dr. Barbara Hecker: five 
adults removed from the mussels by Dr. 
Ruth D. Turner, and a juvenile collected 
from washings of a clump of mussels. 
It was of particular interest to compare 
these polynoids, commensal with the un- 
named, non-hydrothermal, lai^e. Gulf of 
Mexico mussels (to be described and named 
by Ruth Turner and Barry Wilson), with the 
polynoids commensal with the large mus- 
sels in the Galapagos hydrothermal vents. 
recently described under the name Bathy- 
modiolus thertnophilus by Kenk and Wilson 
(1985). The Galapagos polynoids were re- 
ferred earlier to a new genus and species, 
Branchipolynoe symmytilida, in a new 
subfamily of the Polynoidae, Branchipoly- 
noinae (Pettibone 1984). The Gulf of Mex- 
ico commensals are referred herein to a new 
species of Branchipolynoe, B. seepensis. 
The types are deposited in the National 
Museum of Natural History, Smithsonian 
Institution (USNM). 
Branchipolynoinae Pettibone, 1984 
Branchipolynoe Pettibone, 1984 
Type species.?Branchipolynoe symmy- 
tilida Pettibone, 1984. 
The generic diagnosis is emended to in- 
clude Branchipolynoe seepensis, new species, 
commensal with deep-sea mussels in the 
Gulf of Mexico. 
Diagnosis, emended.?Bianchiae smaU to 
well developed, arborescent, on all para- 
podia from segment 2 or 3. Prostomium 
bilobed, with anterior lobes subtriangular 
or rounded, with or without minute frontal 
filaments; median antenna with ceratophore 
indistinct, style short; palps short to long. 
First or tentacular segment visible dorsally 
as short ring or fused to prostomium. Par- 
apodia subbiramous or biramous; notopo- 
VOLUME 99, NUMBER 3 445 
dia small, nodular or conical with projecting 
acicular process; notosetae few (0-3) or 
moderate in number (5-20). Neuropodia 
with or without truncate lobes enclosing 
conical acicular lobes; neurosetae very nu- 
merous, upper ones much stouter or only 
slightly stouter than lower ones. Commen- 
sal with deep-sea mussels at hydrothermal 
vents or hypersaline seep-sites. 
Key to the Species of Branchipolynoe 
1. Elytra small, leaving greater part of 
dorsum uncovered (Pettibone 1984, 
figs. 1, 2A). Arborescent branchiae 
beginning on segment 2 (Pettibone 
1984, figs. 2A, 3A). Anterior lobes 
of prostomium with minute frontal 
filaments (Pettibone 1984, ?g. 2A). 
First or tentacular segment visible 
dorsally as small ring (Pettibone 
1984, ?g. 2A). Parapodia subbira- 
mous, with notopodia small and 0 
to few notosetae (Pettibone 1984, fig. 
3F). Neuropodia with truncate lobes 
enclosing conical acicular lobes (Pet- 
tibone 1984, fig. 3F). Upper neuro- 
setae much stouter than lower neu- 
rosetae (Pettibone 1984, ?g. 31, K). 
Ventral papillae on segments 11 and 
12 short (Pettibone 1984, fig. 4C). 
Commensal with deep-sea mussels 
in Galapagos hydrothermal vents . 
 B. symmytilida Pettibone, 1984 
- Elytra large, leaving middle third of 
body uncovered (Fig. lA). Arbores- 
cent branchiae beginning on segment 
3 (Fig. 2B). Anterior lobes of prosto- 
mium without frontal filaments (Fig. 
lA). Tentacular segment fused to 
prostomium, not visible dorsally as 
separate ring (Fig. lA). Parapodia 
biramous, with notopodia large, con- 
ical, with moderate number of no- 
tosetae (Fig. 2C, D). Neuropodia 
without truncate lobes enclosing 
conical acicular lobes (Fig. 2D). Up- 
per neurosetae only slightly stouter 
than lower neurosetae (Fig. 2H, I). 
Ventral papillae on segments 11 and 
12 long (Fig. ID). Commensal with 
deep-sea mussels in hypersaline seeps 
in Gulf of Mexico  
B. seepensis, new species 
Branchipolynoe seepensis, new species 
Figs. 1-4 
Material. ?Gulf of Mexico, from dives of 
Alvin in 1984, associated with mussels near 
hypersaline seeps at base of Florida Escarp- 
ment, in dark iron-sulfide sediment: Dive 
1343,9 Mar, 26?02'24"N, 84''54'48"W, 3266 
m, from washings of clump of mussels, ju- 
venile paratype (USNM 98782).?Dive 
1344, 12 Mar, 26?02'N, 84?54' 48"W, 3270 
m, from mantle cavities of mussels, holo- 
type (USNM 98779), 2 paratypes (USNM 
98780).-Dive 1346, same data, 2 para- 
types (USNM 98791). 
Measurements. ? Holotype (USNM 
98779) 31 mm long, 13 mm wide, including 
setae, with 21 segments. Two adult para- 
types (USNM 98780) 27-28 mm long, 11- 
13 mm wide, with 21 segments. Two small- 
er aduh paratypes (USNM 98781) 12-16 
mm long, 5-7 mm wide, with 21 segments. 
Juvenile paratype (USNM 98782) 8 mm 
long, 3.5 mm wide, with 18 segments, last 
2 very small. 
Description.?Body short, spindle-shaped, 
slightly tapered anteriorly and posteriorly, 
flattened ventrally and strongly arched dor- 
sally. Fully-developed worms having 21 
segments, first achaetous, with 10 pairs of 
elytra attached on large, low elytrophores 
on segments 2, 4, 5, 7, 9, 11, 13, 15, 17 and 
19. Elytra (Figs. lA, E-G, 3A, B, 4C, D) 
moderately large, oval, covering lateral 
thirds of body on larger adults and nearly 
covering body on juvenile. Elytra oval, 
opaque, smooth, soft, and attached near 
middle on first pair and eccentrically at- 
tached near their anterior borders on fol- 
lowing elytra, sometimes showing branched 
"veins." Dorsal cirri on non-elytra-bearing 
446 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Fig. 1. Branchipolynoe seepensis, holotype (USNM 98779): A, Dorsal view of anterior end, right first elytron 
removed; B, Ventral view of anterior end; C, Dorsal view of posterior end showing segments 19 to 21 and 
pygidium, tenth elytra of segment 19 removed; D, Ventral view of right side of segments 10 to 13 showing 
elongate ventral papillae on segments 11 and 12; E, Right first elytron from segment 2, with "veins" indicated; 
F, Right fifth elytron from segment 9; G, Right tenth elytron from segment 19. Scales = 1.0 mm for A-C; 2.0 
mm for EMj. 
segments having short cylindrical cirro- 
phores and short styles with slender tips, 
extending to about tips of neurosetae (Figs. 
2B, E, 3D, 4E). Dorsal tubercles on cirri- 
gerous segments indistinct. Branchiae well 
developed, arborescent, with rather short 
terminal filaments (Fig. 2B-F, J). Branchiae 
emerging from body in two short trunks, 
lower smaller group attached dorsal to bases 
of notopodia or cirrophores of dorsal cirri 
and upper larger one attached to lateral bas- 
es of elytrophores or dorsal tubercles. 
Fig. 2. Branchipolynoe seepensis, holotype (USNM 98779): A, Right elytragerous parapodium from segment 
2, anterior view, acicula dotted; B, Right cirrigerous parapodium from segment 3, posterior view, cirrophore of 
dorsal cirrus hidden from view; C, Right cirrigerous parapodium from segment 8, posterior view; D, Right 
elytragerous parapodium from segment 9, anterior view, acicula dotted, branchiae cut off; E, Lower branchia 
fi^m same; F, Upper branchia from same; G, Three neurosetae from same, with detail of tips; H, Upper 
neuroseta from same, with detail of tips; I, Lower neuroseta from same, with detail of tips; J, Right elytragerous 
parapodium from segment 15, anterior view, acicula. Scales = 1.0 mm for A-F; 0.1 mm for G?I. 
VOLUME 99, NUMBER 3 447 
448 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Fig, 3. Branchipolynoe seepensis, smaller adult paratype of 12 x 5 mm {USNM 98781): A, First elytron, 
with "veins" indicated; B, Middle elytron; C, Ventral view of right side of segments 11 and 12, showing elongate 
ventral papillae; D, Right middle cirrigerous parapodium, posterior view; E, Right middle elytragerous para- 
podium, anterior view, acicula dotted; F, Three notosetae from same, with detail of tips; G, Upper neuroseta 
from same, with detail of tips; H, Two lower neurosetae from same, with detail of tips. Scales = 0.5 mm for A, 
B; 1.0 mm for C; 0.5 mm for D, E; 0.1 for F-H. 
Branches of branchiae somewhat flattened 
and spread anteriorly and posteriorly be- 
tween parapodia. Branchiae beginning on 
segment 3 as 2 small groups (Fig. 2B), be- 
coming larger with more numerous branch- 
es in middle region (Fig. 2C), and smaller 
posteriorly (Figs. IC, 2J). Branchiae smaller 
on smaller adults (Fig. 3D, E), very small 
and incompletely developed on juvenile 
(Fig. 4E, F). 
VOLUME 99, NUMBER 3 449 
Fig. 4. Branchipolynoe seepensis, juven?e paratype, 8 x 3.5 mm, (USNM 98782): A, Dorsal view of anterior 
end, median antenna and palps missing; B, Ventral view of anterior end; C, Right first elytron; D, Right middle 
elytron; E, Right cirrigerous peirapodium, posterior view; F, Right elytragerous parapodium, anterior view, 
acicula dotted; G, Notoseta from same, with detail of tip; H, Upper neuroseta from same, with detail of tip; I, 
Two lower neurosetae from same, with detail of tips. Scales = 1.0 mm for A, B; 0.5 mm for C-F; 0.1 mm for 
G-I. 
Prostomium (Figs. lA, B, 4A, B) oval, 
bilobed, with rounded anterior lobes lack- 
ing frontal filaments. Median antenna, lack- 
ing distinct ceratophore, inserted in anterior 
notch; short, conical, with slender tip; ven- 
trolateral palps rather short, thick, smooth, 
and tapered, extending beyond prostomi- 
um; lateral antennae and eyes lacking. First 
or tentacular segment fused to prostomium 
and not distinct dorsally; tentaculophores, 
lateral to prostomium, achaetous, short and 
bulbous, each with pair of short cirriform 
tentacular cirri with slender tips, about as 
long as palps (Figs. lA, B, 4A, B). Second 
or buccal segment bearing first pair of large 
elytrophores and elytra, biramous parapo- 
dia with smaller conical notopodia with up 
to 9 notosetae, and larger rounded neuro- 
podia with numerous slender neurosetae and 
lower buccal cirri attached basally, similar 
to tentacular cirri (Figs. lA, B, 2A, 4A, B). 
Mouth ventral with lateral and posterior lips, 
enclosed in tentacular and buccal segments 
(Figs. 1B, 4B). Thick muscular pharynx ex- 
tended on one of paratypes (USNM 98780), 
with opening pulled tightly together; when 
cut open, 5 pairs of small, delicate, oval 
papillae around opening and 2 pairs of small 
jaws, lacking denticulated bases (similar to 
that figured for B. symmytilida, Pettibone 
1984, ?g.2F,G), revealed. 
Biramous parapodia having short conical 
450 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
notopodia and long conical neuropodia 
(Figs. 2B~D, J, 3D, E, 4E, F). Notosetae 
moderate in number (up to 20 on adults, up 
to 5 on juvenile), short to long, extending 
nearly to tips of neuropodia; stouter than 
neurosetae, acicular, smooth or slightly 
roughened distally, with tips rounded (Figs. 
2G, 3F, 4G). Presetal acicular lobes of neu- 
ropodia slightly longer than postsetal lobes. 
Neurosetae very numerous, long, slender, 
separated by slight gap into upper supra- 
acicular and lower subacicular groups. Up- 
per neurosetae slightly stouter than lower 
ones, minutely serrated, with blunt tips (Figs. 
2H, 3G, 4H), some with terminal bulb (Fig. 
2H, upper right). Lower neurosetae more 
slender and having hooked tips with some 
longer denticles (Figs. 21, 3H, 41). Ventral 
cirri, attached to middle of neuropodia, 
short, tapered, and not reaching tips of neu- 
ropodia (Fig. 2C, D). 
Pygidium rather large and bulbous, with 
terminal anus and pair of stout anal cirri 
basally fused; enclosed in parapodia of last 
two posterior segments (20, 21) and their 
long dorsal cirri (Fig. IC). Distinct segmen- 
tal or nephridial papillae not present, except 
for 2 pairs of long ventral papillae on seg- 
ments 11 and 12, projecting posteriorly (Fig. 
1D). Papillae shorter on smaller adult para- 
type (Fig. 3C), absent on juvenile. 
Etymology. ? Neo-Latin adjective see- 
pensis, formed from seep, in reference to the 
distribution of the species in the hypersaline 
seeps in the Gulf of Mexico. 
Remarks, ?According to the preliminary 
report by Denoux et al. (1985), the che- 
mosynthetic vent-type taxa found in hy- 
persaline, cold water, hydrocarbon seeps in 
the Gulf of Mexico are associated with an 
abundance of non-chemosynthetic species 
and this enhanced community diversity 
suggests the possibility that the oil seep 
communities may be the progenitors of those 
at the deep-water vent sites and, thus, more 
primitive. There are some indications that 
the Gulf of Mexico commensal, B. seepen- 
sis, might very well be more primitive than 
the Galapagos commensal, B. symmytilida. 
In B. seepensis, the parapodia are biramous, 
with large notopodia and a moderate num- 
ber of notosetae; the neuropodia have the 
form of conical acicular lobes, following the 
usual pattern in the Polynoidae. In B. sym- 
mytilida, the parapodia are subbiramous, 
with the notopodia small, nodular, and the 
notosetae few to none; the neuropodia have 
an extra truncate lobe enclosing the acicular 
lobe, thus, the development of a new struc- 
ture. There is greater development of the 
arborescent branchiae in B. symmytilida 
than in B. seepensis. 
Acknowledgments 
I wish to thank the Florida Escarpment 
Cruise Participants and especially Drs. Bar- 
bara Hecker and Ruth Turner for the ma- 
terial on which this study is based. The 
manuscript benefited from the reviews of 
Drs. Meredith L. Jones, Nancy J. Maciolek, 
and James A. Blake. 
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VOLUME 99, NUMBER 3 451 
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Department of Invertebrate 2^Dology, Na- 
tional Museum of Natural History, Smith- 
sonian Institution, Washington, D.C. 20560.