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SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 312

Pelagic Copepods of the Family Oithonidae (Cyclopoida) from the East Coasts of Central and South America

Frank D. Ferrari and Thomas E. Bowman

SMITHSONIAN INSTITUTION PRESS

City of Washington

1980

ABSTRACT

Ferrari, Frank D., and Thomas E. Bowman. Pelagic Copepods of the Family Oithonidae (Cyclopoida) from the East Coasts of Central and South America. Smithsonian Contributions to Zoology, number 312, 27 pages, 15 figures, 1 table, 1980.—Twelve species of cyclopoid copepods of the family Oithonidae are described from eastern coastal waters of Central and South America from Belém, Brazil, to Belize City, Belize. Three are new species: Oithona bjornbergae, O. fonsecae, and Paroithona flemingeri. Sexes of O. plumifera are very similar in the copepoid V stage; the male characters (lack of rostrum, flap on cephalosome and pore signature, and extra outer setae on swimming leg exopods) are acquired during the final molt. Several morphological characters besides the traditional ones are used to separate species: the pattern of male integumental organs (pore signature), the armature of the female genital segment, and the modified endopod setae of the female fourth swimming leg. Spermatophores were found ventrally on urosome segments of O. oculata and O. plumifera. It is suggested that during mating the male grasps the female fourth legs with his geniculate first antennae as in Cyclops, and tactile recognition of the male pore signature is accomplished by the modified endopod setae of the female fourth leg.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavernosa Linnaeus).

Library of Congress Cataloging in Publication Data

Ferrari, Frank D.

Pelagic copepods of the family Oithonidae (Cyclopoida) from the east coasts of Central and South America

(Smithsonian contributions to zoology; no. 312)

Bibliography: p.

Supt. of Docs. no.: SI 1.27:312

1. Oithona—Classification. 2. Paroithona—Classification. 3. Crustacea—Classification. 4. Crustacea—South America—Classification. 5. Crustacea—Central America—Classification. 6. Crustacea—Atlantic Ocean—Classification. I. Bowman, Thomas E., joint author. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to zoology; no. 312.

QL1.S54 no. 312 [QL444.C73] 591′.08s [595′.34] 79–607098

Contents

Introduction

Methods

Characters

Genus Oithona Baird, 1843

Subgenus Dioithona (Kiefer), 1935

Oithona oculata Farran, 1913

Subgenus Oithona Baird, 1843

Oithona amazonica Burckhardt, 1912

Oithona bjornbergae, new species

Oithona decipiens Farran, 1913

Oithona fonsecae, new species

Oithona hebes Giesbrecht, 1891

Oithona nana Giesbrecht, 1892

Oithona neotropica Herbst, 1967

Oithona plumifera Baird, 1843

Oithona setigera Dana, 1853

Oithona simplex Farran, 1913

Oithona sp. 1

Oithona sp. 2

Genus Paroithona Farran, 1913

Paroithona flemingeri, new species

Commentary

Literature Cited

Requirements for Smithsonian Series Publication

Pelagic Copepods of the Family Oithonidae (Cyclopoida) from the East Coasts of Central and South America

Frank D. Ferrari and Thomas E. Bowman

____________

Frank D. Ferrari, Smithsonian Oceanographic Sorting Center, Smithsonian Institution, Washington, D.C., 20560. Thomas E. Bowman, Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C., 20560.

Introduction

From 11 June to 18 July 1977, one of us (FDF) accompanied the Scripps Institution of Oceanography RV Alpha Helix on a cruise from Belém, Brazil, in the mouth of the Amazon River, along the east coast of Central America to Belize City, Belize. Numerous samples were taken for the Smithsonian Oceanographic Sorting Center (SOSC) in nearshore waters from the Alpha Helix or small skiffs working closer to shore. Most zooplankton samples analyzed in this study were taken by hand-towing an open conical net from a small skiff through shallow, subtidal waters. Net velocity was kept low to minimize loss of appendages, spines, and setae of delicate oithonids. In addition to SOSC samples, specimens were studied from Alpha Helix Station 5.5 (belonging to Scripps Institution of Oceanography Plankton collection) and NMNH-STRI Stations 55 and 126 (from the Panama Survey conducted by the National Museum of Natural History and the Smithsonian Tropical Research Institute). Two unusual oithonid males were sorted from RV Melville Stations 353 and 359 in the eastern Pacific Ocean. Although collected beyond the strict geographical limits of this study, these specimens are used to illustrate the variation in integumental organ patterns. A list of stations with locality data and general notes is given in Table 1.

We wish to thank Dr. Abraham Fleminger, chief scientist of the cruise, for the opportunity to collect biological samples. We are also especially appreciative of the efforts of Dr. William Overall, Department of Invertebrates of the Museo Goeldii in Belém, without whose help the very valuable samples from the mouth of the Amazon River would not have been collected, and Drs. Meredith Jones, Department of Invertebrate Zoology, National Museum of Natural History, and David Judkins, Brookhaven National Laboratories, for contributing samples and specimens that have added much to our basic knowledge of oithonids. Our special thanks are also extended to Mr. Richard Hammer for reviewing the manuscript.

METHODS.—Plankton samples were fixed initially in 4% formaldehyde buffered with sodium tetraborate. Prior to examination in the laboratory, oithonids were transferred to distilled water and then 70% ethanol, the final preservative. Specimens to be studied with a light microscope were first cleared in lactic acid and then stained with a solution consisting of approximately 1% by weight chlorazol black E dissolved in 70% ethanol (as described in Fleminger, 1973) added to lactic acid. The amount of stain added and time of exposure (15–60 minutes) varied depending upon the species and condition after preservation. All staining was carefully monitored. When prepared in this manner, many details of oithonid external morphology could be examined and compared prior to dissection. Drawings were made with the aid of a camera lucida; for most appendages an oil immersion lens was used. Type material is deposited in the National Museum of Natural History (NMNH) under the collection numbers of the former United States National Museum (USNM).

TABLE 1.—Station information for all samples studied

Females and males of some abundant species were studied with a scanning electron microscope (SEM) to better understand several characters used in differentiating various species. Specimens in 70% ethanol/30% water were brought through baths of 80%/20% and 90%/10% to 100% ethanol. From this solution they were transferred through two dilutions, 66% ethanol/33% amyl acetate and 33%/66% to 100% amyl acetate, the transition fluid for critical point drying. Standard critical point drying techniques were used to prepare specimens for gold coating prior to SEM examination.

Results of preparation by this procedure were not particularly encouraging. The thin cuticle of species of Oithonidae was easily wrinkled during this preparation, giving a distorted perspective when studied with the SEM. Thus we were never sure how much information was lost during preparation, which made interpretation of detail more difficult. Nevertheless some of the better micrographs are presented. As would be expected examination of the cuticle of oithonids with the SEM reveals a whole series of new morphological structures. Generally we confine our comments to those structures that can be observed with the light microscope and of whose systematic value we have some appreciation.

The following abbreviations are used in the text and illustrations:

Pr

prosome

Cph

cephalosome

Pg

pediger

Ur

urosome

CR

caudal ramus

A1

first antenna

A2

second antenna

Md

mandible

Mx1

first maxilla

Mx2

second maxilla

Mxp

maxilliped

P

swimming leg

B

basipod

Re

exopod

Ri

endopod

Se

external seta or spine

Si

internal seta or spine

St

terminal seta or spine

CHARACTERS.—The important characters traditionally used to differentiate species within the family Oithonidae are armature and development of the Md and Mx1, shape of the rostrum and CR, and number of Se and ReP1–4. Definitive description of a species has been based on the anatomy of the female. Males have presented difficulties due to the sexual dimorphism in the above-mentioned characters, particularly the rostrum, shape of CR, Se on ReP1–4, and in some cases the armature of B2Md. Among small oithonid species sexual dimorphism in size is not pronounced; males and females are often collected in plankton nets with small mesh widths. As species increase in size, sexual dimorphism in size becomes more pronounced (Giesbrecht, 1892). Thus large females are often collected with standard plankton nets, while the conspecific smaller males are lost through the larger mesh widths of these nets. Matching males with females has often depended solely on cooccurrences in samples (Rosendorn, 1917); this method is especially unreliable when sexual dimorphism in size is pronounced.

In addition to the above-mentioned characters we will emphasize several others that have been found particularly useful in previous studies. The RiP4 of the female may possess one to three setae modified from the usual plumose condition. The number and extent of the modification have been used in a few species descriptions (Giesbrecht, 1892; González and Bowman, 1965; Wellershaus, 1969; Bowman, 1975; Ferrari, 1977; and Fonseca & Björnberg, 1977). These modified setae seem less fragile than plumose setae and are often present when tips of the others have been broken. The modifications involve the thickness, curvature, and presence of a distal flange. The specific differences, pronounced in many species, are often obscure in those that exhibit a great degree of overall morphological similarity. The armature of the knob on the genital segment near the female genital opening has also proven to be of taxonomic value; hence, illustrations of the female urosome are presented in lateral view. Ornamentation of other urosome segments, although not developed in all species, is also useful. The pattern of tiny hairs on B1 and 2 of P4 often shows distinct differences between species. However, because these hairs are easily broken off or lost in preparation and the patterns difficult to see even in the best stained specimens, we have not emphasized their usefulness in our descriptions.

Male animals continue to present problems. The presence and shape of the lateral flap of the Cph and the accompanying pattern and number of integumental organs are useful in differentiating males (Ferrari, 1977). The flap appears as a thin, almost transparent, extension of the Cph. It may extend over Pg1 or Pg1 and 2. The articulations of the Pg's can be seen beneath the flap although these articulations are not shown in our drawings of the organ patterns. The flap is apparently not attached to the Pg's. A general impression of the integumental organ pattern (hereafter referred to as the “pore signature” of Mauchline and Nemoto, 1977; “pore signature pattern” of Fleminger, 1977, seems redundant) can be observed in lateral view of a carefully stained male. Dissection of the Cph and flap allows a more exact mapping of position and number of organs. Separation of males of otherwise morphologically similar species is still difficult; we have not had enough material to do a thorough analysis of variation within any one species or between two similar species. The armature of the mouthparts, especially Ri and Re of Md and Mx1, are difficult to study because they are easily broken or missed during dissection and examination but remain important in matching males with females.

We initially felt the structure of the geniculate A1 would also be useful in differentiating males; however, studies with the light microscope and SEM have not proved useful. Telescoping of segments at the proximal geniculation prevents a clear interpretation of the number, size, or armature of the segments. In addition, the segments are seldom fixed in a consistent alignment, permitting accurate comparison between them.

Genus Oithona Baird, 1843

Subgenus Dioithona (Kiefer), 1935

Oithona oculata Farran, 1913

FIGURES 1, 15a

Oithona oculata Farran, 1913:188–189, pl. 30: figs. 8–10; pl. 31: figs. 2, 3.—González and Bowman, 1965:273–274, fig. 20h, i.—Nishida et al., 1977:139–140, fig. 13.

MATERIAL.—Numerous and from PN-13-60, PN-18-60, PN-32-200, PN-35-200, PN-50-200, PN-55-200, PN-58-200, and PN-59-200.

FEMALES.—Length range (30 specimens) 0.61–0.80 mm; Pr/Ur-1.6. Ri2P4 (Figure 1a) with both setae modified, slightly curved toward their tips; proximal seta with serrate flange on distal of medial edge; distal seta with serrate flange on distal ¼. Ri3P4 proximal seta similarly modified with serrate flange on distal . Knob near genital opening (Figure 1b) armed with anterodorsally curved spine, bearing tiny distinct teeth on posterior margin; below this spine a small point.

MALES.—Length range (30 specimens) 0.59–0.70 mm; Pr/Ur-1.5. Cph in lateral view (Figure 1d) produced into a small triangular extension near posterior ventral edge. Extension not homologous to flap previously described for O. dissimilis and O. hebes (Ferrari, 1977) or those of other oithonids in this paper; in these species posterior edge of Cph visible beneath translucent flap. Cph with a few integumental organs scattered over the lateral surface but not placed in a distinctive pattern. Organs (Figure 15a) with form of shallow pore without thickened peripheral ridge; small hair arises from the center of pore. Cph pitted with slight circular depressions, smaller in diameter than pore.

FIGURE 1.—Oithona oculata, a, P4; b, Ur, lateral; c, Url and 2, lateral, with spermatophore. d, Cph, lateral.

REMARKS.—Specimens of O. oculata agree with recent description by González and Bowman (1965). The dorsal ridge, which they describe on the female genital segment, is depicted in lateral view as a simple notch along the dorsal edge of the segment. Two kidney-shaped spermatophores were attached to several females and have helped in understanding features of the genital segment. As in females of the family Cyclopidae, the spermatophores are attached ventrally on the genital segment with an adhesive substance on the anterodorsal edge of the spermatophore (Figure 1d). A small tubule passes dorsally from the spermatophore. We have not yet identified the genital in opening in any oithonid. It may be located near the termination of the spermatophore tube, but it appears that the tubule empties instead into a sulcus or groove formed by two ridges of the integument. The ridges, depicted by heavy lines in Figure 1b,c, extend dorsally on each side of the armed knob of the genital segment. The position of the ridges, one to the other, appears to vary slightly and these changes can occasionally produce various stress lines on the cuticle. We atempted to study this area under SEM but the integument folded and buckled during preparation.

Subgenus Oithona Baird, 1843

Oithona amazonica Burckhardt, 1912

FIGURE 2

Oithona amazonica Burckhardt, 1912:726; 1913:422, pl. 15P: figs. 6–22; pl. 15Q: figs. 2, 3; pl. 16R: figs. 2–4, 7–9, 11, 12; pl. 16s: figs. 1, 3–8, 17.

Oithona amazonica continentalis Lindberg, 1954:193–195, fig. 1.

MATERIAL—3 and 3 from PN-8-260.

FEMALE.—Lengths 0.61, 0.60, 0.60 mm; Pr/ Ur-1.3, 1.3, 1.4. ReP1 (Figure 2e) with 1–1–3 Se. St Re3P1 seta-like (see “Remarks”); Se ReP2 11–3, ReP3 1–1–1, and ReP4 0–0–1; St Re3P2–4 well developed. Ri3P4 with both setae unmodified; Ri3P4 proximal seta straight, slightly thickened, with serrate flange on distal 2/3 of medial edge (Figure 2h). Knob near genital opening armed with a minute, slender spine (Figure 2b).

MALE.—Length of specimens 0.57, 0.56, 0.55 mm; Pr/Ur-1.7, 1.5, 1.6. Se ReP1 1–1–3 (Figure 2k); Se ReP2–4: 1–1–3, 1–1–1, 0–0–1; St Re3P1–4 well developed; Ri3P4 proximal seta not modified. Cph and flap (Figure 2j) not dissected from specimens. Pore signature similar to hebes/fonsecae pattern (described under O. fonsecae) but with distinct hiatus between dorsal horizontal row and 2 anterior columns of organs making up anterodorsal cluster. In O. hebes and O. fonsecae longitudinal row proceeds into and is continuous with anterodorsal cluster.

REMARKS.—A fundamental difficulty with the female of this species is the armature of RePl. Generally species of Oithona bear either a seta, often reduced, or a series of hairs on the inner margin of Re1; Re2 bears a well-developed plumose seta; Re3 usually bears four internal plumose setae, the distalmost in juxtaposition to the terminal spine. Se on these segments are not as stiff as those on the other swimming legs. Each Se is ornamented on both sides with a hyaline membrane, often reduced, whose outer edge is serrate. Distally it continues as a flexible whiplike extension, unique to Pl.St of Re3 is a distinctively thickened, rigid structure with a well-developed, serrate, hyaline membrane on its lateral edge. The medial edge may be naked or plumose along most or all of its length. By convention, St is omitted from counts of the external spines although in some earlier accounts it was included.

Our specimens agree in most respects (e.g., length range, armature of Md and P2–4) with 0. amazonica, first described by Burckhardt in 1912 and described and illustrated by him in 1913. However, St of Re3P1 looks like the other four Si; the lateral membrane is absent and both margins are plumose. The distal Se is longer than the two proximal Se. Burckhardt's (1913) drawing shows two Se on Re3P1, which he records, and distally a longer spine in a more terminal position, which he obviously considered the St. He states that the proximal of the three Se of Re3 is absent. However, Burchkardt makes no particular note of the number of Si on Re3; these are not illustrated. If there were five, then his St would correspond to the third and distal, Se, the true St, as in our specimens, being replaced by a seta. If there were only four Si, his interpretation of the armature would be fundamentally correct and the morphological differences would warrant a new name for our specimens. We have also noted, incidentally, that Burckhardt's (1913) identification of his illustrations corresponds to the citations in the text, but the letters and numerals on the illustrations themselves are discordant; figures 13 J, K, and L should read as 13 K, L, and M; 14 M and N as 14 N and O; 15 O and P as 15 P and Q; 16 Q and R as 16 R and S; 17 S and T as 17 U and V.

Lindberg (1954) based his subspecies, O. amazonica continentalis, from Rio Negro near Manaos, on the replacement of all Se on ReP1 by setae. If such major differences occur in the armature of this appendage, his subspecies should be recognized as a new species. Lindberg's illustration of Pl, like Burckhardt's, is difficult to interpret. The Se are drawn as setae. However, these structures, with their whiplike extensions and often reduced hyaline membranes, might have been mistaken for setae by Lindberg.

Without a more thorough survey of the lower Amazon River basin, it is difficult to determine if the above-discussed specimens belong to three distinct species or to the same species originally described by Burckhardt. Certainly the diversity and complexity of oithonid species in the mouths of large tropical rivers may be much greater than has been realized to date. With the discovery of the new species described below, there are at least three species in the east coast drainages of South America, O. gessneri Kiefer, 1954 (described twice by Kiefer, 1954, 1956), from the Orinoco River and O. amazonica and O. bjornbergae from the Amazon River.

FIGURE 2.—Oithona amazonica, a, habitus, lateral; b, Ur, lateral; c, CR. dorsal; d, Md; e, Pl; f, P2; g, P3; h, P4. i, habitus, lateral; j, Cph and flap; k, Pl.

FIGURE 3.—Oithona bjornbergae, a, habitus, lateral; b, anterior part of head, dorsal; c, Ur, lateral; d, Ur2–4, ventral; e, CR, dorsal; f, Al; g, A2; h, Md; i, Mxl;j, Mx2; k, Mxp; l, Pl; m, P2; n, P3; o, P4.

Oithona bjornbergae, new species

FIGURES 3, 4

MATERIAL,—Numerous and from PN-1-60, PN-5-60, PN-6-60, PN-7-60, and PN-8-60.

FEMALE.—Length range (30 specimens) 0.44–0.51 mm; Pr/Ur-1.4. Head rounded in dorsal view; rostrum absent (Figure 3a). Ur2–4 fringed on posterolateral margin; Ur2 and 3 with 1 transverse row of minute hairs on ventral surface near posterior margin (Figure 3d); Ur4 with 2 rows. CR length 2 times width; apical seta 2 and 3 thickened, with shorter, more dense plumes than other setae, (Figure 3e). A1 and 2 similar to other species of Oithona. B2Md (Figure 3h) with 2 thick, curved spines of equal length, bearing fine spinules; Ri with 4 plumose setae; Re 4-segmented with 4 setae. B2Mx 1 (Figure 3i) with 2 thin spines bearing thick spinules; Ri absent; Re with 3 setae. Mx2 and Mxp as in Figure 3j, k; Se ReP1–4: 1–1–2, 1–1–2, 0–1–1; 0–0–1; Si Re1P1 absent. Both

Setae on Ri2P4 and proximal seta on Ri3P4 modified; all straight; proximal seta of Ri2 with small serrate flange on distal ; flange well developed on distal of distal seta of Ri; proximal seta of Ri3 slightly thicker than others with flange on distal Knob near genital opening armed with a small spine (Figure 3c).

MALE.—Length range (30 specimens) 0.41–0.48 mm; Pr/Ur-1.4. Head rounded dorsally, laterally slightly more acuminate than female (Figure 4a). As in O. oculata, Cph with triangular extension posteriorly toward ventral margin. Articulation along dorsal part of triangle poorly developed as shown by broken line in Figure 4a and thinner line in Figure 4b. Cph with few unorganized sensory hairs and pores, which differ in structure from those of pore signature in most oithonids. Ur3–6 fringed on posterior edge; Ur3 and 4 with 1 transverse row of minute hairs on ventral surface near posterior margin; Ur5 with 2 rows (Figure 4d). All apical spines and dorsal spine of CR thickened. Genital flap with 1 large seta; below it several tiny toothlike spines. A1 as in Figure 4e; remaining appendages similar to female except Ri2 and 3P4, which lack modified setae.

FIGURE 4.—Oithona bjornbergae, a, habitus lateral; b, Cph, lateral; c, Ur. lateral: d, Ur3–6 and CR, ventral; e, A1.

REMARKS.—The spine count of ReP1–4 of O. bjornbergae is identical to that of only one other oithonid, O. gessneri Kiefer, 1954. Kiefer twice described this as a new species (1954, 1956) from female specimens. In neither publication were the mouthparts or modified setae on Ri2 and 3P4 described. Although the size (0.5 mm) of the single specimen of O. gessneri reported in 1954 is comparable to that of O. bjornbergae, the latter females can be readily separated by the middle two thickened apical setae on the CR and the transverse rows of tiny hairs ventrally on Ur2–4. Kiefer reports (1954) and illustrates (1956) tiny hairs ventrally on the posterior margin of Ur3–5. In Kiefer (1956), at the bottom of page 262, exopod 1 is identified as exopod 2.

Oithona gessneri was collected in a lagoon of the Orinoco River near Barrancas, Venezuela; O. bjornbergae was found in the flowing waters of the Rio Guama and Rio Acara Granda of the Amazon River drainage. Without further survey it is impossible to determine whether these species are isolated in separate drainages, separated simply by habitat (flowing or standing waters), or cooccur.

ETYMOLOGY.—This species is named for Dr. Tagea K. S. Björnberg, Brazilian carcinologist, who has contributed to our understanding of many copepods, including the oithonids.

TYPE MATERIAL.—Female holotype (USNM 172183), 37 and 28 paratypes (USNM 172184, 172185) from PN-7-260, 01°27.8'S, 48°29.2′W, mouth of Rio Araca Granda, Para, Brazil; 11 Jun 1977.

Oithona decipiens Farran, 1913

FIGURE 5

Oithona decipiens Farran, 1913:184–185, pl. 28: figs. 4–11.—Kiefer, 1929:7.—Mori, 1937:111, pl. 61: figs. 9–14.—Chen et al., 1974:32, pl. 2: figs. 1–5.—Nishida et al., 1977:183–184, fig. 7.

MATERIAL.—34 from PN-13-60.

FEMALE.—Length range 0.60–0.72 mm. Knob near genital opening armed with a single, thick, curved spine, toothed on posterior edge (Figure 5a). Ri2P4 both setae modified (Figure 5b), slightly curved; distal thicker than proximal, with more well-developed flange on distal ; proximal with flange on distal ¼. Ri3P4 proximal setae thickened with flange on distal .

FIGURE 5.—Oithona decipiens, a, Ur, lateral; b, P4.

REMARKS.—Our specimens agree with those described and illustrated by Farran (1913). Nishida et al. (1977) report some specimens with 0–0–1 Se on ReP4. For reasons that will be presented in the discussion section, we agree with Kiefer (1956) that variation in spine number is important in separating species. A more extensive survey of the area around Sagami Bay should be made in order to resolve the reported variation.

Oithona fonsecae, new species

FIGURE 6

MATERIAL.—5 from PN-11-60, 31 and 37 from PN-23-60, 1 from PN-43-200, and 8 from PN-70-200.

FEMALE.—Length range 0.49–0.60 mm; Pr/ Ur-1.4. Head rounded in dorsal and lateral views (Figure 6a, b). Pg4 with tiny hairs along posterolateral border. Url (Figure 6d) dorsal surface with 2 long central hairs followed by a long transverse row of smaller hairs, roughly U-shaped; posterior and lateral to this row, 2 rows separated by a gap at midwidth. CR length 3 times width. B2Md (Figure 6f) with 2 thick, slightly curved spines bearing small spinules; Re 5-segmented with 5 setae; Ri with 5 setae, lateralmost plumose; 1 small setae arising near base of Ri. RiMx1 (Figure 6g) with 3 setae, 1 arising near base; B2Mx1 with 3 spines, 2 with long marginal spinules. Se ReP1–4: 1–1–3, 1–1–3, 1–1–3, 1–1–2; Re1P1 with 1 Si. Ri2P4 proximal seta slender, without flange; distal seta much thicker, slightly curved with well-developed flange on distal ; Ri3P4 proximal seta longer and thinner than distal setae of Ri2, curvature less pronounced, flange on distal ¼. P5 with small seta near base. Knob near genital opening with spine curved dorsally, ventral to this a second smaller spine (Figure 6c).

MALE.—Length range 0.49–0.51 mm; Pr/Ur-1.5. Head slightly more truncate than female in dorsal view, laterally rounded; rostrum absent. Flap of Cph tongue-shaped, reaching slightly beyond Pg1. Pore signature (Figure 6k) similar to that of O. hebes; anterodorsal cluster of 2 oblique columns; followed posteriorly by long horizontal row; ventral to horizontal row, 11 columns, the last on Cph flap. Ventrally each column continues anteriorly as a horizontal series of organs; the first 2 columns appear continuous through a horizontal series. In addition to 11th (last) column, Cph flap has several peripheral organs and 2 smaller oblique rows extending from dorsal edge of flap. CR length 2 times width. B2Md (Figure 6n) with 2 spines; much thinner than on female, 1 naked, other ornamented with thicker, longer spinules than in female. Remaining aspects of Md and Mx1 similar to female, although slightly reduced. Armature of P1–4 as in female except Si Ri2 and 3P4 not modified. P5 with reduced seta at base. Genital flap with 1 long plumose seta and reduced seta ventral to it.

REMARKS.—Several small species of Oithona, which inhabit the eastern tropical coastal waters of South America, have been described with the same number of Se on ReP1–4: O. hebes Giesbrecht, 1891; O. ovalis Herbst, 1955; O. neotropica Herbst, 1967; O. oligohalina Fonseca and Björnberg, 1977; and this new species. Females of all except O. ovalis and O. oligohalina were collected during this study; males of only O. fonsecae and O. hebes were collected. Characters helpful in separating females of O. fonsecae are the rounded shape of head in lateral view; five setae on RiMd and the reduced seta at the base of RiMd; slight differences in modified setae of Ri2 and 3P4; hairs on posterior edge of Pg4 and Url; armature of knob near genital opening; length/wide ratio of CR. Males of O. fonsecae can be separated from O. hebes by the five setae on RiMd and the reduced seta at its base.

ETYMOLOGY.—This species is named for Dr. Vera Lucia Fonseca, Brazilian carcinologist, in recognition of her work on habitat partition by closely related species of Oithona.

TYPE MATERIAL.—Female holotype (USNM 172186), 27 and 31 paratypes (USNM 172187, 172188) from PN-23-60, 09°34.6′N, 78° 59.5′W, in small lagoon of Caobos Cay in Hollandes Cay Group, between Mayflower Channel and Caribbean Sea, Panama, 30 Jun 1977.

FIGURE 6.—Oithona fonsecae, : a, habitus, lateral; b, anterior part of head, dorsal; c, Ur, lateral; d, Url, dorsal; e, CR, dorsal; f, Md; g, Mx1; h, P1; i, P4. : j, habitus, lateral; k, Cph and flap; l, CR, dorsal; m, A1; n, Md; o, Mx1.

Oithona hebes Giesbrecht, 1891

FIGURE 7, 15

Oithona hebes Giesbrecht, 1891:475.—Ferrari, 1977:406–407, figs. 3C-D, 4, 5.

MATERIAL.— and from PN-11-60, PN-13-60, PN-19-60, PN-21-60, PN-27-60, PN-32-200, PN-33-200, PN-43-200, PN-46-200, PN-65-200, PN-65-200, PN-67-200, PN-70-200, NMNH-STRI Sta 55, and NMNH-STRI Sta 126.

REMARKS.—Oithona hebes has been redescribed from specimens from the type-locality, the Gulf of Guayaquil (Ferrari, 1977). We present here several points not mentioned in that study, but which agree with specimens reexamined from Guayaquil, the Pacific coast of Panama, as well as those from the east coast of Central America. Head of female distinctly quadrate in lateral view (Figure 7a). Distal seta of Ri2P4 (Figure 7c) thicker than proximal seta of Ri3P4 but not so great a difference as shown in Figure 3D of Ferrari (1977). P5 with reduced seta at base (Figure 7b). Knob near genital opening with a single well-developed spine, not a small point. Male P5 with reduced seta at its base. A more complete illustration of the pore signature from the dissected Cph and flap is shown here (Figure 7d). Previous illustrations (Ferrari, 1977) were made from the entire animal. The major features of the pore signature (anterodorsal cluster, horizontal row, 11 vertical columns ventrally, each extended anteriorly by a horizontal series, peripheral organs, and two oblique rows on cephalosomal flap) agree very closely with O. fonsecae males.

FIGURE 15b-e shows SEM micrographs of parts of O. hebes pore signature. In Figure 15b (left side) the anterodorsal cluster is shown in the center of the field. The integument has cracked along the dorsal horizontal row (to the left) although the first few organs of that row can be seen. Ventrally the integument has curled and only the top organs of the columns can be seen.

Figure 15c is a view of the anterodorsal cluster. Each integumental organ consists of a pore, guarded on one side by a thin ridge. The relief of this ridge appears variable for those organs in the cluster. It is this ridge that is visible under the light microscope. Short hairs can be seen associated with most ridges under the light microscope, although they are absent in the micrograph. Figure 15d, badly distorted due to buckling, is the right side of another male. Organs of the anterodorsal cluster are visible in the top right corner; the dorsal horizontal row passes obliquely toward the lower left corner. These pores also seem to have distinct ridges associated with them. In the center are several columns that extend into horizontal series. Figure 15e is another view of the conjunction of column to horizontal series. Distinct ridges also appear to be associated with the pores of columns. In contrast, the pores of horizontal series are surrounded by slightly thickened integument.

FIGURE 7.—Oithona hebes, : a, anterior part of head, lateral; b, Ur, lateral; c, P4. : d, Cph and flap; e, anterodorsal pore signature clusters from left sides of 3 other specimens.

Variation in the pore signature can be noted in specimens examined with the light microscope. We have not had enough specimens, however, to study differences between inter- and intraspecific variation. For this reason we have not been able to find consistent differences between the pore signature of O. fonsecae and O. hebes. Figure 7e shows the anterodorsal cluster from the left side of three specimens of O. hebes from PN-27–60. A line has been drawn to separate the two oblique rows composing each cluster. Not only do the positions of the organs shift, relative to one another, but in the third cluster there are 10 organs in the upper row and 12 in the lower; these counts on the other two specimens are 11/12. Besides O. hebes, O. nana and O. simplex were the only other species collected at this station. Because their pore signatures are distinctly different, we have not confused several species in this case. Before males of O. hebes and O. fonsecae can be separated, information from series of specimens of both species throughout their ranges must be obtained and a thorough study of intraspecific variation undertaken.

Oithona nana Giesbrecht, 1892

FIGURE 8

Oithona nana Giesbrecht, 1892:538–546, pl. 34: figs. 10–11, 20, 24, 26, 34, 35, 42; pl. 44: figs. 2, 4, 6.—González and Bowman 1965:272, fig. 20 c-g.—Nishida et al., 1977:138–139, figs. 11, 12.

MATERIAL.— and from PN-11-60, PN-13-60, PN-18-60, PN-20-60, PN-21-60, PN-23-60, PN-25-60, PN-26-60, PN-27-60, PN-29-200, PN-30-200, PN-32-200, PN-33-200, PN-34-200, PN-35-200, PN-36-200, PN-37-200, PN-38-200, PN-43-200, PN-44-200, PN-45-200, PN-46-200, PN-49-200, PN-55-200, PN-56-200, PN-57-200, PN-58-200, PN-59-200, PN-62-200, PN-64-200, PN-65-200, PN-67-200, PN-70-200, Alpha Helix Sta 5.5, and NMNH-STRI Sta 126.

FEMALES.—Length range (30 specimens) 0.58-0.72 mm; Pr/Ur-1.1. Ri1P4 (Figure 8c) with a distinct row of 4 long spines; O. nana is the only species encountered with surface armature on RiP1–4. Ri2P4 (Figure 8c) with both setae modified; neither seta strongly curved, both with flange on distal 3/5; Ri3P4 proximal seta similar, with flange on distal 3/5. P5 elongate, with several long hairs dorsal to it on posterior margin of Ur1. Knob near genital opening armed with short, thick spine and longer seta.

MALE.—Length range (30 specimens) 0.47–0.53 mm; Pr/Ur-1.3. Flap of Cph (Figure 8e) relatively broader and shorter than in O. hebes and O. fonsecae; it reaches middle of Pg1. Pore signature significantly different; anterodorsal cluster roughly circular; posterior to this a poorly defined horizontal group of organs usually followed by 5 distinct columns. Ventral organs of columns also appear as continuation of horizontal group. Cph flap with less distinct series of columns much more closely spaced. Below horizontal group an area devoid of organs and ventral to this, a group of poorly organized organs along ventral part of Cph and flap.

Intraspecific variation in the pore signature has been observed in this species. In another specimen, on the right side, organs in the horizontal group anterior to the 5 distinct columns appear organized into a smaller 6th column (Figure 8f, g). This new column simply may have resulted from shifting in position of the organs; such shifting has been noted in O. hebes. On the right side of a 3rd specimen, a distinct gap behind a horizontal group was followed by only 4 columns; on left side gap was absent and 6 columns were present (Figure 8h, i).

REMARKS.—Oithona nana has been described numerous times; recent useful accounts are González and Bowman (1965) and Nishida et al. (1977).

FIGURE 8.—Oithona nana, : a, habitus, lateral; b, Ur, lateral; c, P4. :d, habitus, lateral; e, Cph and flap; f-g, left and right pore signatures of second ; h-i, same of third .

Oithona neotropica Herbst, 1967

FIGURE 9

Oithona neotropica Herbst, 1967:96–101, figs. 1–12.

[?] Oithona oligohalina Fonseca and Björnberg, 1977:127–131, figs. 1–4.

MATERIAL.—6 from PN-13-60 and 2 from PN-43-200.

FEMALE.—Length range 0.56–0.64 mm; Pr/Ur-1.3. Head broadly pointed dorsally, laterally distinctly quadrate; rostrum absent (Figure 9a, b). Pg4 with hairs on posterior border. CR length 3 times width. B2Md (Figure 9d) with 2 slightly curved, robust spines bearing tiny spinules; Ri with 5 setae. Ri3P4 distal seta thickened, slightly curved, with flange on distal ½; Ri3P4 proximal seta straight with flange on distal ½ (Figure 9e). Knob near genital opening with a curved spine and below it a smaller straight spine (Figure 9c).

FIGURE 9.—Oithona neotropica, : a, habitus, lateral; b, anterior part of head, dorsal; c, Ur, lateral; d, Md; e, P4.

REMARKS.—In our opinion the type-locality and only locality reported for O. neotropica, Laguna Mucubaji, Venezuela, is erroneous. Collections in Laguna Mucubaji were made by Fritz Gessner during German expeditions to Venezuela in 1952 (Gessner, 1956) and 1963 (Gessner and Hammer, 1967). Copepods from the 1952 expedition were reported on by Kiefer (1956); the only copepod from Laguna Mucubaji was a new subspecies, Metacyclops leptopus mucubajiensis Kiefer. Copepods from the 1963 expedition were given to Herbst (1967), who found two species from Laguna Mucubaji, Acartia tonsa Dana and Oithona neotropica. Other crustaceans from Laguna Mucubaji were typical freshwater Cladocera (Brehm, 1956).

Acartia tonsa and Oithona spp. are marine and estuarine species, and it is surprising that Herbst did not comment on their anomalous occurrence in Laguna Mucubaji. Acartia tonsa tolerates reduced salinities better than most other marine calanoids (Lance, 1963, 1964) but it does not survive in freshwater. In Delaware Bay Cronin et al. (1962) found a few specimens at salinities below 1 but the usual lower limit was about 5 . Laguna Mucubaji is located in the Venezuelan Andes at 8°39′N, 70°49′W at an elevation of 3560 m, more than 50 km SE of Lake Maracaibo. Dissolved minerals are very low; Gessner and Hammer (1967) report the following: μS 11, alkalinity 0.1, pH 6.7.

The location, elevation, and low mineral content of Laguna Mucubaji and the presence of freshwater crustaceans exclude the possibility that Acartia tonsa and Oithona neotropica could survive there. Perhaps there was a mixup of labels in Gessner's collections. The true type-locality of O. neotropica is unknown, but it seems likely that the sample supposedly taken in Laguna Mucubaji actually came from coastal waters of Venezuela.

Herbst describes and figures O. neotropica with four setae on RiMd. The setae on this appendage are easy to miss; the quadrate head, CR (3 times as long as wide), and Se ReP1–4 (1–1–3, 1–1–3, 1–1–3, 1–1–2) would seem to distinguish females of this species. Fonseca and Björnberg (1977) described O. oligohalina from low salinity waters of a coastal lagoon near Cananeia, Brazil, in the state of São Paulo. There seems little difference between O. oligohalina and O. neotropica except habitat preference and number of setae on RiMd, which we have already commented upon. The possible separation needs further investigation.

Oithona plumifera Baird, 1843

FIGURES 10, 15f

Oithona plumifera Baird, 1843:59.—Kiefer, 1929:4.—Mori, 1937:109, pl. 60: figs. 3–15.—Sewell, 1947:255.—Nishida et al., 1977:140–142, figs. 14, 15.

MATERIAL.— and from PN-13-60, PN-14-60, PN-18-60, PN-19-60, PN-20-60, PN-21-60, PN-23-60, PN-25-60, PN-26-60, PN-29-200, PN-32-200, PN-33-200, PN-35-200, PN-58-200, PN-59-200, PN-62-200, PN-63-200, and Alpha Helix Sta 5.5.

FEMALE.—Length range (30 specimens) 1.06–1.28 mm; Pr/Ur-1.1. Ur2 (Figure 10a) with tuft of hairs on anteroventral surface and small row of spinules posterior to knob near genital opening; knob with small, thin spine and spinule ventral to it. As Crisafi (1958) has noted, Ur4 with 2 rows of 4 thick hairs on anteroventral margin; lengths of hairs increase laterally (Figure 10b); Ur5 with lateral and dorsal rows of hairs (Figure 10c). CR also with hairs on posteromedial edge. A1 with tiny hairs, without associated pores, on 1–10 free segments (Figure 15f); Ri2P4 both setae modified; thick, curved with flange over distal ; curvature of distal seta more pronounced; Ri3P4 with proximal seta modified; thick, slightly curved toward tip, with flange on distal . Re3P4 St plumose on distal of medial edge. P5 with hairs on medial edge.

MALE.—Length range (30 specimens) 0.59–0.68 mm; Pr/Ur-1.5. Cph flap (Figure 10h) much thinner than O. hebes; digitiform; attenuate end reaching beyond posterior edge of Pg1. Pore signature similar to O. hebes. Anterodorsal cluster not organized into columns; posterior to this, horizontal row curves ventrally onto Cph flap and converges with 11th column. Ventral to horizontal row 10 distinct columns on Cph; 11th on flap. Ventrally, columns continue anteriorly as horizontal series. Posterior to 11th column, flap with 2 chevrons and peripheral organs along posterior edge.

REMARKS.—Males of this species agree in Se ReP1–4 with Nishida et al. (1977), not with Wellershaus (1970), who apparently mistakenly cited Giesbrecht (1892). Giesbrecht's descriptions and illustrations (table 44, figs. 12–15) clearly show O. plumifera males with 1–1–2, 1–1–3, 1–1–3, 1–1–2 Se on ReP1–4.

Spermatophore placement similar to O. oculata (Figure 10d). Spermatophore placed ventral to tuft of hairs on genital segment but is attached to Ur1, not to genital segment as in O. oculata. Tubule connecting spermatophore to sulcus much thicker and appears as central duct with surrounding sleeve.

Sexual dimorphism in O. plumifera may not be confined to structures directly involved in copulatory behavior (which generally appear only in copepodid VI, the adult stage) but is manifested in other external structures, such as the rostrum (present in females; absent in males) and number of Se ReP1–4 (1–1–2, 1–0–2, 1–0–1, 0–0–1 in females; 1–1–2, 1–1–3, 1–1–3, 1–1–2 in males). For this reason we initially felt females and males could be distinguished at copepodid V. We decided to separate copepodid V specimens to determine if immature males possessed a flap on the Cph and accompanying pore signature. The sample from Alpha Helix Sta 5.5, from a small lagoon on Klein Bonaire, was chosen for study since it contained numerous adults and copepodids of only two oithonids, O. nana and O. plumifera. Both females and males of O. nana have 1–1–3, 1–1–3, 1–1–3, 1–1–2 Se ReP1–4. Smaller copepodids with those Se numbers were considered immature O. nana. All large copepodids possessed a rostrum and 1–2–2, 1–0–2, 1–0–1, 0–0–1 Se ReP1–4; they appeared to be immature females of O. plumifera. Upon closer examination, however, one specimen was found to be a mature male within the immature exoskeleton described above. The animal was captured during its final molt and possessed male attributes, no rostrum, flap on Cph with pore signature, and 1–1–2, 1–1–3, 1–1–3, 1–1–2 Se. Apparently male and female copepodid V's are morphologically similar and resemble the female in those dimorphic characters present. The male copepodid V then undergoes significant morphological reorganization. During the final molt of ontogenetic development, the male acquires a number of Se on ReP1–4. It is interesting to note that Burckhardt (1913) assumed that the phylogenetic trend in females has been toward a reduction in the number of these spines from the basic 1–1–3, 1–1–3, 1–1–3, 1–1–3 numbers exhibited by O. simplex.

FIGURE 10.—Oithona plumifera, : a, Ur, lateral; b, Ur4, ventral; c, Ur5 and CR, dorsal; d, Ur1 and 2 with attached spermatophore, lateral; e, A1; f, P4. : g, habitus, lateral; h, Cph and flap.

Oithona setigera Dana, 1853

FIGURE 11

Oithona setigera Dana, 1853:1101–1102, pl. 76: fig. 6a-f.—Kiefer, 1929:6.—Mori, 1937:110, pl. 60: figs 1, 2.—Sewell, 1947:257.—Nishida et al., 1977:147–149, figs. 19–20.

MATERIAL.—2 from PN-14-60 and 1 from PN-25-60.

FEMALE.—Length of females 1.62, 1.69, and 1.57 mm; Pr/Ur-0.9, 0.9, and 0.9. Knob near genital opening with short, straight, thick spine, denticulate on posterior edge and small spine ventral to it (Figure 11a). Ur4 ventrally with 2 rows of 5 or 6 hairs, increasing in length laterally (Figure 11b). Ri2P4 (Figure 11e) both setae modified, thick, curved, with flange on distal ; proximal seta on Ri3P4 virtually straight, but thicker, with flange on distal ½. P5 with hairs on medial edge.

FIGURE 11.—Oithona setigera, : a, Ur1 and 2, lateral; b, Ur4, ventral; c, P4.

REMARKS.—Nishida et al. (1977) have noted variation in this species. Our three specimens were in such poor condition that we cannot comment on intraspecific variation. Oithona setigera, like many oithonids, is in need of a thorough zoogeographic analysis.

Oithona simplex Farran, 1913

FIGURES 12, 15g, h

Oithona simplex Farran, 1913:187–188, pl. 29: figs. 10–14; pl. 30: figs 1, 2.—González and Bowman, 1965:274, fig. 21f-i.—Chen et al., 1974:74, pl. 3: figs. 1–3.—Nishida et al., 1977:151–152, fig. 23.

MATERIAL.—Numerous and from PN-11-60, PN-19-60, PN-19-60, PN-20-60, PN-21-60, PN-23-60, PN-25-60, PN-26-60, PN-27-60, PN-32-200, PN-32-200, PN-33-200, PN-44-200, PN-45-200, PN-46-200, PN-65-200, PN-66-200, PN-67-200, PN-70-200, and NMNH-STRI Sta 126.

FEMALE.—Length range (30 specimens) 0.37–0.41 mm; Pr/Ur-1.6. Ri2 and 3P4 Si without curvature or flange, simple and plumose yet shorter and thinner than remaining Si (Figure 12c). Knob near genital opening with small, thin spine medially, a smaller spine ventrally, and a tiny spine dorsally (Figure 12b).

MALES.—Length range (30 specimens) 0.41–0.50 mm; Pr/Ur-1.5. Cph similar to female, without flap. Pore signature a series of columns with some connection ventrally between columns, suggesting horizontal series; without anterodorsal cluster (Figures 12d, g, 15g). Individual pores without well-developed ridges; integument slightly thickened anteriorly and posteriorly (Figure 15h).

REMARKS.—Oithona simplex has recently been discussed and illustrated by González and Bowman (1965) and Nishida et al. (1977).

FIGURE 12.—Oithona simplex, : a, habitus, lateral; b, Ur, lateral; c, P4. : d, Cph.

Oithona sp. 1

FIGURE 13a-c

MATERIAL.—1 from PN-13-60.

FEMALE.—Length 0.74 mm; Pr/Ur-1.1. Anterior end of head swollen, terminating in small pointed rostrum laterally (Figure 13a). B2Md elongate, with 2 large spines bearing spinules; Ri with 4 setae, 1st and 4th longer and plumose. ReP1–4, Se 1–1–3, 1–1–3, 1–1–2 (distal Se of Re3 missing), 1–1–2. Ri1P4 Si missing (Figure 13c); Ri2P4 proximal Si missing; distal thick, straight with flange on distal Ri3P4 proximal Si missing. Knob near genital opening (Figure 13b) with long flexible seta, shorter, stiff spine ventrally, and reduced spine dorsally.

REMARKS.—This specimen is in very poor condition; one exopod each of P3 and P4 and many spines and setae missing. It is similar to O. vivida of Nishida et al. (1977) and Chen et al. (1974) in these features: lateral profile of head, number and shape of Se ReP1–4, and elongate seta on knob near genital opening. The number of setae on RiMd differs, but these are easily broken or missed.

We agree with Nishida et al. (1977), as well as Rosendorn (1917), that Farran (1913) probably reversed figures 7 and 8 of plate 27 (pp. 2, 3). Although Farran did not illustrate P4, he states that “exopodite appears to have 1–1–3 or 1–0–3 slender minute outer edge spines.” These spines on our specimen and that of Nishida et al. (1977), although slender, are not minute and there are only two on Re3P4. Farran shows a smooth tapering rostrum in lateral view, not swollen and then tapering to a point. Rosendorn (1917), who apparently had several specimens of O. vivida, describes them with 1–1–3 Se on ReP4, although her specimens differ from Farran's in the armature of B2Md, RiMd, and ReMx1. We must concur with Kiefer (1956) concerning the importance of number and shape of Se on ReP4. Specimens described by Nishida et al. (1977) appear to belong to a new species to which ours could be assigned, but we choose not to erect a new species on the basis of a single specimen.

Oithona sp. 2

FIGURE 13d,e

MATERIAL.—1 from PN-13-60.

MALE.—Length 0.57 mm; Pr/Ur-1.5. Rostrum absent; head rounded in lateral view. Cph flap a right triangle, reaching middle Pg1 (Figure 13e); ridge parallel to ventral edge of cephalosome divides pore signature. Anterodorsal cluster well developed with 7 or 8 rows of organs; dorsal 4 rows continue posteriorly as horizontal row; behind this a chevron-shaped column followed by 4 columns. Ventral to ridge a large number of organs, organized anteriorly in horizontal patterns, posteriorly as vertical or oblique rows. ReP1–4 Se 1–1–3, 1–1–3, 1–1–3, 1–1–2; P5 with single seta; genital flap with small bump armed with thick (probably elongate) seta (broken in this specimen) and a smaller seta dorsally (Figure 13d).

FIGURE 13.—Oithona sp. 1, : a, anterior part of head, lateral; b, Ur, lateral; c, P4. Oithona sp. 2, : d, habitus, lateral; e, Cph and flap. Oithona sp. 3, : f, Cph and flap. Oithona sp. 4, : g, Cph and flap.

REMARKS.—This specimen differs from any previously described male. Females of O. decipiens, Oithona sp. 1, and Paroithona flemingeri, new species, from PN-13–60 have not had males attributed to them. Assuming this male belongs to one of these species, only P. flemingeri can be eliminated on the basis of size and number of endopodal segments of the swimming legs. Since only one specimen is available, we have not dissected the appendages and thus confined our descriptive account to those characters that could be observed on the whole animal.

Genus Paroithona Farran, 1913

Paroithona flemingeri, new species

FIGURE 14

MATERIAL.—38 from PN-13-60.

FEMALE.—Length range 0.40–0.45 mm; Pr/Ur–1.2. Head rounded in lateral view, rostrum absent (Figure 14a). CR (Figure 14d) slightly longer than wide; dorsal and 1 apical seta thick and elongate, bearing lateral hyline membrane similar to StP1–4 of most oithonids; 2 apical setae absent; lateral seta reduced. A1 (Figure 14e) with 1 free segments. A2 with 1st segment elongate (Figure 14f). B2Md (Figure 14g) with 1 large, thick, slightly curved spine, bearing spinules and 1 small, thin seta in inferior position; ReMd 4 segments, terminal seta reduced; RiMd a bump with 4 setae. RiMx1 (Figure 14h) naked. Mx2 and Mxp as illustrated (Figure 14i, j). ReP1 2-segmented; Re2 and 3 fused; ReP2–4 3-segmented, ReP1–4 2-segmented. ReP1–4 Se 1–3, 1–1–2, 1–0–2, 1–0–1; ReP1–4 Si 0–4, 0–1–5, 0–1–5, 0–0–5; RiP1–4 Se 0–1, 0–1, 0–1, 0–1; RiP1–4 Si 1–6, 0–3, 0–3, 1–3. All Si RiP4 unmodified. P5 with 1 seta. Knob near genital opening with 1 spine pointing posterodorsally and below this 1 thinner spine (Figure 14b).

REMARKS.—Paroithona flemingeri is most easily separated from the two other species of the genus by number of Se ReP1–4; P. parvula: 1–3, 1–1–2, 1–1–2, 1–1–1; P. pulla: 1–3, 1–1–2, 1–0–1, 0–0–1 (not 1–1–2 for ReP3 as listed in Wellershaus, (1970) table).

ETYMOLOGY.—The species is named for Dr. Abraham Fleminger, who has contributed so much to our understanding of the systematics of free-swimming marine copepods.

TYPE MATERIAL.—Female holotype (USNM 172189), 34 paratypes (USNM 172190) from PN-13-60, 10°41.2′N 63°14.2′N, 800 m from jetty at Carupano, Venezuela; 22 Jun 1977.

Commentary

About 60 species have been placed in the family Oithonidae since Baird's (1843) initial description of Oithona plumifera. Despite the amount of information that has accumulated about oithonids over the past century, there are still difficulties in assigning values to characters studied in standard systematic accounts. Aside from denoting characters that have intrinsic value in classification, simply because they do vary, knowledge of the biology of oithonids is of such a poor state that there has been no attempt to order these characters in a system reflecting the evolutionary trends of the animals. Over 50 years have passed since the only attempt was made to relate several species within the genus Oithona (Burckhardt, 1913).

As an example of the lack of basic biological information, we know of no direct observations of oithonid mating behavior. However, this behavior in other gnathostome cyclopoids of the family Cyclopidae has received attention from a number of authors, e.g., Hill and Coker (1930) and Rylov (1948). These observations indicate that males use their digeniculate first antenna to grasp the ReP4 of the female. Their ventral surfaces are facing. There is some question as to whether this is the initial contact position or whether the male moves to this position from a previous one, grasping the Pr/Ur articulation of the female dorsally (Hill and Coker, 1930). Nonetheless the male must reach the A1/P4 position in order to attach the spermatophores ventrally on the female genital segment over the ventrally placed female genital openings. Spermatophore transfer is affected with the tips of the male swimming legs. Thus spermatophores can be transferred by use of virtually unspecialized swimming legs; specialized appendages or seta need not have evolved for this purpose as Ferrari (1977) has suggested.

FIGURE 14.—Paroithona flemingeri, : a, habitus, lateral; b, Ur, lateral; c, Ur1 and 2, dorsal; d, CR, dorsal; e, A1;f, A2;g, Md; h, Mx1;i, Mx2; j, Mxp; k. P1; l, P2: m, P3; n, P4.

Although no observations have been published on mating behavior of oithonids, certain observations suggest a similar pattern of events. Female genital openings in the Oithonidae are dorsal or dorsolateral in position but spermatophores are attached to females of O. plumífera and O. oculata ventrally as in the Cyclopidae. It is not known whether the male grasps the female as in Cyclops, at the ReP4. Assuming that he does, however, one might expect to find a tactile recognition system during this positioning and the system may be reflected in the morphology of the appendages involved. No study of the complex male digeniculate Al has been undertaken to enumerate differences between species. However, distinct differences in numbers and shapes of spines on ReP4 have been used quite commonly in separating species of oithonids, and the taxonomic value of these structures has been emphasized by Kiefer (1956).

If the position of male/female at the time of spermatophore transfer is similar to the final mating position of, e.g., Cyclops amencanus, as illustrated by Hill and Coker (1930, fig. 2), the female could use the specialized setae of RiP4 for tactile interrogation of the male pore signature prior to spermatophore transfer. All females of the genus Oithona have modified setae on RiP4, although in O. simplex these setae are reduced rather than bearing a flange. Not all males possess a well organized pore signature, however. Oithona oculata and O. bjornbergae lack this pore signature, although in SEM micrographs, the lateral surface of Cph of O. oculata is densely pitted.

Observations of living oithonids will eventually elucidate the functions of modified setae on RiP4 of females and pore signature of males. Because of their value in systematic studies, we feel it would be beneficial to know the role these structures play in the biology of oithonids. If it is shown that these integumental organs function in some interrogating system during reproduction, this would suggest their importance in a speciation process emphasizing the development of prezygotic isolating mechanisms. Further, an effort should be made to collect males of closely related species over their entire zoogeographic range, so that the general organization and intraspecific variation of the pore signature can be characterized and compared to the variation between species. Once the extent of intraspecific variation is understood, more difficult problems can be addressed, such as characterization of populations, definition of population boundaries, and extent of interpopulation movements.

FIGURE 15.—Oithona oculata, : a, integumental organ of cephalosome, × 10,000. Oithona hebes, : b, anterodorsal cluster, anterior part of horizontal row, and several vertical columns with their horizontal continuations, × 2000; c, anterodorsal cluster, × 7500; d, 2nd d, right side, anterodorsal cluster, part of horizontal row, and several vertical columns with their horizontal continuations, × 2000; e, 1st 2 vertical columns and horizontal continuations, × 5000. Oithona plumífera, : f, hairs on Al. Oithona simplex. , right side: g, pore signature, × 1800; h. single pore. (Micrographs reduced to 44%.)

Regardless of their denouement in the evolution of the genus Oithona, several types of pore signatures can be recognized in species studied. All species possess vertical columns of organs, which are interconnected ventrally. This pattern is present even in O. simplex, which possesses the fewest number of organs and no Cph flap. Except for O. simplex, all species possess a distinct anterodorsal cluster of organs. Two males (Figure 13f, g) from Melville Stations 359 and 353, respectively, although geographically beyond the scope of this study, serve to emphasize the importance of this anterodorsal cluster. Oithona sp. 3 (male) is 0.80 mm long with the same spine count as Oithona plumifera (1–1–2, 1–1–3, 1–1–3, 1–1–2). The pore signature and flap development (Figure 13f) is similar to O. plumifera. However, the anterodorsal cluster has more organs than O. plumifera and these seem more densely spaced. In O. plumifera (Figure 10h) there is a rather abrupt transition between the anterodorsal cluster and horizontal row. On Oithona sp. 3 the transition is immediate but the horizontal row begins as a jumbled group of organs before resolving into the single row.

Oithona sp. 4 (male) is 0.76 mm long; the spine count on ReP1–4 is 1–1–3, 1–1–3, 1–1–3, 1–1–2. The pore signature is also similar to O. plumifera. The anterodorsal cluster (Figure 13g) is composed of more organs than O. plumifera or the previous male. It merges rather indistinctly, again via a jumble of organs, into the horizontal row, which eventually resolves into a single row of organs.

The anterodorsal cluster can be considered the anterior end of the horizontal row of organs, the third general feature of the pore signature. This row is either set dorsally to the columns, in effect confining them, e.g., O. amazonica, O. hebes, O. plumifera, or appears less distinctly as a forward extension of the ventral organs in the columns as in O. nana and Oithona sp. 2. These latter two males also possess numerous scattered organs ventral to the columns and horizontal row. The organs are separated from columns and row in the former species by an area devoid of organs and in the latter by a ridge of the integument.

All females show modifications of one or more internal setae on the RiP4. These modifications may simply be a reduction in the size of the setae compared to other internal plumose ones as in O. simplex but more often involves development of a medial flange on the tip of a thick seta. One, (O. amazonica), two (O. fonsecae and O. hebes), or three (O. plumifera, O. decipiens, O. oculata, and O. bjornbergae) setae may be modified with varying degrees of curvature; the flange length also varies in relation to the length of seta. These female characters may contain as much taxonomic information as the pore signature. The latter are more easily studied because slight variations in the setae may be reflected in the degree of curvature and length of flange. These are more difficult to analyze than the discrete male organs.

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