A NEW GENUS OF RIDGEWAYIIDAE (COPEPODA: …plesiomorphic characters, thus conﬁrming the primitive...

JOURNAL OF CRUSTACEAN BIOLOGY, 27(2): 339–350, 2007

A NEW GENUS OF RIDGEWAYIIDAE (COPEPODA: CALANOIDA) FROM A KARSTIC

CAVE OF THE WESTERN CARIBBEAN

Eduardo Suarez-Morales and Thomas M. Iliffe

(ES-M) El Colegio de la Frontera Sur (ECOSUR)-Chetumal, A.P. 424. Chetumal, Quintana Roo 77000,

Mexico. Research Associate, National Museum of Natural History, Smithsonian Institution ([email protected]);

(TMI) Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas 77553-1675, U.S.A.

A B S T R A C T

The calanoid copepod family Ridgewayiidae, containing demersal and cave-dwelling forms, has representatives worldwide, but most have

been known from the Northwestern Tropical Atlantic. Eight valid genera were hitherto known, most of them were described recently

(Ridgewayia Thompson and Scott, Exumella Fosshagen, Brattstromia Fosshagen and Iliffe, Placocalanus Ohtsuka, Fosshagen and Soh,

Exumellina Fosshagen and Iliffe, Normancavia Fosshagen and Iliffe, Robpalmeria Fosshagen and Iliffe, Stargatia Fosshagen and Iliffe).

Biological collections in cave environments in an island off the Caribbean coastline of Honduras, Central America, showed the presence

of ridgewayiid copepods. These specimens were found to belong to an undescribed genus of the family. The new genus Hondurella is

distinguished from the other eight known ridgewayiid genera by a combination of characters that include a simple rostrum with no

filaments, maxilliped with modified setae, first leg with a modified exopod and a reduced endopodal armature, and most importantly,

a female fifth leg with a slightly modified exopod and a 1-segmented endopod, plus a reduced right exopod of the male fifth leg, and the

presence of spines on the middle segments of the male right antennule. As all other ridgewayiids, the new genus retains several

plesiomorphic characters, thus confirming the primitive profile of this family. The distribution of Ridgewayiidae in the Caribbean region

remains largely unknown, but it is suggested that distributional patterns and a relatively high degree of endemism are related to the

geological origin and dynamics of the area. Aside the modified maxillipedal setae, mouthparts in the new genus,are normally developed;

this, together with our observations of the gut contents, suggest that this ridgewayiid is more a particle-feeder than a carnivorous form.

INTRODUCTION

The family Ridgewayiidae is among the most representativecopepod taxa in anchialine and cave environments (Fos-shagen et al., 2001). Ridgewayiids have some exclusivelycave-dwelling genera, but some other forms occur inepigean environments such as corals, different types ofdemersal habitats, and at least one species has been knownto be associated to an actiniarian (see Humes and Smith,1974). There are eight genera of the Ridgewayiidae knownto date (Fosshagen and Iliffe, 1991, 2003). Most of them,aside the genus Ridgewayia, which was described more thanone century ago by Thompson and Scott (1903), weredescribed recently. Some of these genera are monotypic,i.e., Brattstromia, Exumellina, Robpalmeria, Normancavia,whereas Ridgewayia is the most species rich, with 12nominal species known to date (Boxshall and Halsey, 2004).The highest diversity of this peculiar family is concentratedin the Northwestern Tropical Atlantic, particulary in theCaribbean area, but representatives of this family have beenrecorded in subtropical and tropical latitudes worldwide(Ohtsuka et al., 2000; Fosshagen and Iliffe, 2003; Boxshalland Halsey, 2004).

Ridgewayiids are deemed as primitive copepods (Fos-shagen and Iliffe, 2003) because of the presence of severalplesiomorphic characters in both the mouthparts andswimming legs. The female fifth leg exhibits a characteristicmodification of the exopod, the third segment is insertedmedially on an expanded second segment. The male fifthlegs are modified and have a variable degree of complexity,particularly in the exopodal rami.

Epibenthic and zooplankton samples were collected byone of us (T. M. Iliffe) in hypogean habitats of several sites

in the island complex of Utila Bay, in Honduras, CentralAmerica. Only a few records of Ridgewayiidae are knownin Central America, but none south of Belize (Fosshagenand Iliffe, 2003). Samples obtained in anchialine caves atthis site (Fig. 1) contained male and female specimens ofcopepods assignable to the family Ridgewayiidae. Thesespecimens represent an undescribed genus and species.Comments on the distribution and biogeography of thefamily and genus in these areas are also included.

MATERIALS AND METHODS

Zooplankton samples were collected during the summer of different yearsas part of a biological survey to determine the composition, diversity, anddistribution of the freshwater and anchialine fauna of the westernmostsector of the Caribbean Basin, including different areas of Central America.One of these sites, the Hondurean island of Utila, was positive forridgewayiid copepods (see Fig. 1). Biological samples were collected byusing advanced diving techniques dragging a hand net with a fine mesh(100 lm) through the water, or by baited traps. The copepods were sortedout from the original sample and preserved in 70% ethanol. Copepodswere prepared for taxonomic analysis which included dissection of theappendages and staining with Chorazol Black. The appendages weremounted using glycerine as a semi-permanent medium to perform the basictaxonomical examination. Illustrations were prepared with the aid of acamera lucida. Two males and one female were dehydrated and processedto perform SEM observations. Type specimens were deposited in the Col-lection of Zooplankton of El Colegio de la Frontera Sur (ECO-CHZ),Chetumal, Mexico. Five adult specimens were dissected in order to analyzetheir gut contents. Descriptions are based on type material only; observa-tions and details from SEM specimens in figures 7 and 8 are supplementary.

The island of Utila is the smallest of the three major islands in The BayIslands group off the Honduras Caribbean coast; Roatan and Guanaja arethe other two. Utila is located approximately 18 miles (29 km) from theHonduras mainland port of La Ceiba. The island is 11 km long and 4 km atits widest; it is surrounded by vast coral reefs. The island is composed ofboth basaltic lava and coral limestone of Pleistocene to Holocene age.Karstic caves are distributed in the limestone region between Utila Town

339

and Pumpkin Hill; one of these hypogean systems is Byrun’s cave, the sitefrom which these copepods were collected (Station 96-020, 5 May 1996). Itis a karstic cave located in the interior of the island; it consists of a collapsesinkhole, 5 m in diameter with the water level 3 m below the surface of theground. At the bottom of the sinkhole is a crescent-shaped pool, 2 m acrossand up to 6 m deep with a rock and sand bottom. Surface salinity was 1 pptas measured with a refractometer, increasing to 23 ppt at 6 m. A haloclinewas visible at 3 m depth. Collections with the net (0-5 m depth) yieldedmore than 100 copepods in this site. Also observed were amphipods andflatworms.

SYSTEMATICS

Ridgewayiidae M. S. Wilson, 1958(emend. Fosshagen and Iliffe, 2003)

Hondurella new genus

Diagnosis.—Female: Body slender, not compressed laterally.Pedigerous somites 2-3 separated, 4-5 fused. Posterior cor-ners of prosome smooth, rounded. Urosome 4-segmented,with genital double somite asymmetrical, left marginmodified; somite projected ventrally. Caudal rami relativelyshort, slightly shorter than anal somite. Seta V (Huys andBoxshall, 1991) symmetrical on both caudal rami. Rostrumpointed, strong, with single lobe, filaments absent. Anten-nule relatively short, reaching fourth prosome somite, 26-segmented. Antenna with exopod longer than endopod;exopod plesiomorphic, 8-segmented. Mandibular basis with4 setae; endopod 2-segmented, with distal segment having9 setal elements. Maxilliped with 5-segmented endopodbearing some modified setae. Leg 1 with long spiniformexpansions on second exopodal segment; outer spines onthird exopodal segment with subterminal filament. Endopodof leg 1 with reduced number of setae (7). Legs 1-4 with3-segmented endopods and exopods; 3 outer spines onexopods of legs 3 and 4. Leg 5 with third exopodal segmentapparently unmodified except for articulated setae and slightasymmetry of insertion and moderate lateral expansion onsecond exopod; endopod 1-segmented, represented byelongated rod-like structure distally acute.

Male: Body smaller and slenderer than female. Urosome 5-

segmented. Caudal rami and setae symmetrical. Right

antennule 23-segmented, geniculated, with spines on seg-

ments 11 and 12. Mouthparts and legs 1-4 similar to female.

Leg 5 with both endopods reduced, 1-segmented; right

exopod reduced, 1-segmented, left exopod highly modified.

Type Species.—Hondurella verrucosa, new species, heredesignated.

Etymology.—The generic name is a noun in femininegender that makes reference to the country of CentralAmerica, Honduras, where the new copepod was collected.

Hondurella verrucosa, new species(Figs. 2-8)

Material Examined.—Holotype, one adult $, collected byThomas M. Iliffe, 5 May 1996 from Byrun’s Cave, UtilaBay, Honduras, Central America (168069110N, 868539470W,approximate). Specimen dissected, on semi-permanent slide,deposited in the collection of Zooplankton of El Colegio dela Frontera Sur (ECOSUR) in Chetumal, Mexico, undernumber ECO-CHZ-02961. Allotype, one adult #, collectedby Thomas M. Iliffe, same locality and date. Specimenpartially dissected, ethanol-preserved, mouthparts andswimming legs on semi-permanent slides, ECO-CHZ-02960. Paratypes, 6 adult ## , 6 adult $$ collected byThomas M. Iliffe, same locality and date, ECO-CHZ-02962.Specimens undissected, ethanol-preserved. All these speci-mens were collected below the halocline in marine waters.

Description.—Female. Length of prosome: 0.75-0.82 mm(n¼ 7); total length including caudal rami¼ 1.12-1.25 mm(n¼ 7). Holotype total length: 1.20 mm. Body with typicalcalanoid shape, relatively slender, prosome slightly nar-rower anteriorly, widest at midle section of prosome, bodysymmetrical (Fig. 2B). Rostrum strong, wide-based, withoutrostral filaments (Fig. 7D), rostrum visible in lateral view.Fifth pedigerous somite symmetrical, both sides widelyrounded, unmodified, unornamented (Fig. 2A). Intersomitalsuture between fourth and fifth somites complete. Urosome,excluding caudal rami, representing 28% of total bodylength; urosome formed by three somites, proportions as:49: 24: 26 ¼ 100. Genital double-somite relatively large,representing over 50% of urosome length, asymmetrical,with left margin bearing low protuberances, right marginstraight (Fig. 2B). Genital double-somite expanded ventrallyat distal section, latter process associated with wide, asym-metrical genital field and operculum (Figs. 3A, 7A, B);copulatory pore on proximal 1/3 of genital somite (Fig. 7B).Pre-anal somite wih tooth-like hyaline cuticular processeson distal margin, visible ventrally (Fig. 3A). Anal somitesubrectangular, representing about 29% of urosome length,cuticular ornamentations absent on dorsal and ventral sur-faces of urosomites.

Caudal rami lamelliform, subrectangular, symmetrical,

slightly shorter than anal somite; with ventral surface

bearing field of hair-like setae near inner margins of rami;

inner margin lightly pilose from distal half (Fig. 3A). Each

caudal ramus with four terminal, short dorsal seta, plus

one outer spiniform seta. Caudal seta V (sensu Huys and

Fig. 1. The Western sector of the Caribbean area showing general locationof the island of Utila, and Byrun’s Cave, the type locality of Hondurellaverrucosa.

340 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 27, NO. 2, 2007

Fig. 2. Hhondurella verrucosa, new genus and species. Holotype female. A. habitus, laterla view; B. habitus, dorsal view; C. antennule segments 1-23; D.antennule segments 24-26.

341SUAREZ-MORALES AND ILIFFE: NEW CARIBBEAN RIDGEWAYIIDAE

Fig. 3. Hondurella verrucosa, new genus and species. Holotype female. A. urosome, ventral view; B. antenna; C. mandible; D. gnathal blade; E. Maxilla.


Fig. 4. Hondurella verrucosa, new genus and species. Holotype female. A. maxilliped; B. detail of maxilliped showing modified setae; C. first swimmingleg; D. second swimming leg; E. third swimming leg.


Fig. 5. Hondurella verrucosa, new genus and species. Holotype female. A. fourth swimming leg; B. fifth swimming leg; C. exopod of first swimming leg;Allotype male. D. habitus, lateral view; E. urosome, lateral view.


Fig. 6. Hondurella verrucosa, new genus and species. Holotype female. A. maxillule; Allotype male. B. Right antennule segments 1-19; C. right antennulesegments 20-23; D. detail of segments 8-14 showing spines; E. fifth leg; F. fifth leg in different position.


Boxshall, 1991) equally long on both rami. All terminalsetae biserially plumose.

Antennules (Fig. 2C, D) relatively short, 26-segmented,reaching fourth posterior margin of third pedigerous somite.Longest setae on segments 4, 8, 10, 11, 13, 19, and 22.Armature per segments as follows (Arabic numerals ¼segment, Arabic numerals in parentheses¼ number of setae,ae¼ aesthetasc): 1(1), 2(4þ ae), 3(2), 4(1þ ae), 5(1), 6(2þae), 7(2), 8-10(2), 11(1þ ae), 12(1), 13(2þ ae), 14(1þ ae),15(2þ ae),16(1), 17(2þ ae), 18(2), 19(2), 20(2þ ae), 21(1),22(1), 23(2), 24(2 þ ae), 25(2), 26(4 þ ae).

Antenna (Fig. 3B) with exopod slightly longer thanendopod. Coxa with one short, biserially plumose seta.

Basis with two setae on outer distal margin, distalmost abouttwo times longer than proximalmost. Endopod reduced, 2-segmented. First segment long, cylindrical, robust, with oneouter seta inserted on distal 1/3 and inner row of spiniformornamentations. Terminal segment with two lobes; subdistallobe with 7 setae, distal lobe with 5 setae; inner margin ofsecond endopodal segment with two short setae. Exopodprimitive, 8-segmented, armed with one seta on each ofsegments 1-7. Distal exopodal segment longest, with onelong subdistal seta on inner margin, and three long terminalsetae subequal in length and breadth.

Mandible (Fig. 3C) with basis of palp armed withfour short setae, two of them relatively longer, endopod

Fig. 7. Hondurella verrucosa, new genus and species. Non-type female. A. genital somite, ventral view; B. same, showing position of genital pore; C. detailof modified maxillipedal seta; D. rostrum, ventral view; E. exopodal segments of third swimming leg showing cuticular tympani; F. fifth leg showinginsertion of terminal exopodal segment and single-segmented endopod.


2-segmented, proximal segment short, armed with foursetae; distal segment subrectangular, well developed, with9 terminal setae, one on subdistal position noticeablyslenderer and shorter than others. Exopod four-segmented,with 0, 1, 2, 3 setation pattern. Gnathal base with 9-10 wide-based, low anterior teeth, all unicuspate. Ventral teethpoorly developed, barely separated from outer tooth bysmall diastema, dorsal seta short (Fig. 3D).

Maxillule (Fig. 6A) with pre-coxal arthrite bearing 9spiniform setae plus 4 setiform elements. Coxal epipoditewith 9 setae of unequal length and width, biserially setulatedfrom distal half. Coxal endite with four setae. Basis withfirst endite lobe bearing three setae, second basal endite with5 setae. Endopod 3-segmented, first segment with 3 setae,second with 4, distal segment subquadrate, with 6 terminalsetae. Exopod oblong, with 11 subequal setae.

Maxilla (Fig. 3E) indistinctly segmented, coxa and pre-coxa partially fused, with four lobes, two praecoxal and twocoxal; first lobe with 4 setae and one isolated seta, second tofourth lobes each with three long setae. Basal segment withweakly developed basal lobe (allobasis) bearing two setae.Endopod three-segmented, first segment protuberant, withthree setae; second with three setae, and third segmentreduced, with four setae.

Maxilliped (Fig. 4A) well developed. Coxa fused withpraecoxa. Coxa with one slender seta on proximal 1/5, plusthree distinct lobes, proximalmost with two subequal setae,second lobe bearing three equal setae, distalmost coxal lobe

armed with four seta. Basis elongated, with row of hair-likeelements on proximal half and three subequal setae on distalhalf. Endopod 6-segmented. First segment short, partillyfused to basis, with two long setae. Second segment bearingfour setae aligned on distal half of segment; two distalmostsetae modified, branched distally, with hollow parts atinsertion of distal branches (Figs. 4A, B, 7C). Third segmentabout half as long as second, with modified setae; fourthsegment with four setae, fifth with one. Distal endopodsegment with three terminal plus one subterminal seta.

First swimming leg (Fig. 4C) with three-segmentedexopod and endopod. Coxa with coxal seta on internalmargin. Basis with long, curved seta on distal inner marginreaching beyond distal end of second endopodal segment.First endopodal segment with outer margin producedforming rounded protuberance reaching beyond proximal1/3 of second endopodal segment. Second exopodalsegment with three spiniform processes at insertion pointof outer seta. Outer spines on third exopod each with smalldistal accesory seta-like element (Fig. 5C). Second, thirdand fourth legs with 3-segmented exopods and endopods(Figs. 4D, E, 5A); exopods of these legs with large poresnear base of outer spines of three segments (Fig. 7E), exceptfor leg 4, with pores in second and third segments only.

Fifth leg exopod with three segments (Fig. 5B). Exopodslightly modified, second segment moderately producedlaterally, armed with spiniform seta; third segment insertedeccentrically on inner margin of second, armed with outer

Fig. 8. Hondurella verrucosa, new genus and species. Non-type male. A. Rostrum, ventral view; B. fifth leg overview, anterior; C. detail of exopod of leftfifth leg showing process with wart-covered surface (arrowed); D. same, another view, showing distal rounded process with series of thin lamellae.


spiniform setae and inner articulated setae. Endopod withone segment, represented by long rod-like structure taperingdistally to form a pointed end (Figs. 5B, 7F). Armatureformula (Roman numerals indicate spiniform elements,Arabic numerals indicate setae) of swimming legs:

coxa basis exopod endopod

leg 1 0-1 0-1 I-1;I-1;III,1,4 0-1;0-1;1,2,2leg 2 0-1 0-0 I-1;I-1;III,I,5 0-1;0-2;2,2,4leg 3 0-1 0-0 I-1;I-1;III,I,5 0-1;0-2;2,2,4leg 4 0-1 1-0 I-1;I-1;III,I,5 0-1;0-2;2,2,3leg 5 0-0 0-0 I-0;I-1;II,I,4 0-0

Male: Allotype specimen (Fig. 5D) with total length: 1.20mm; mean length of other male specimens: 1.10 mm (n¼4).Length of prosome: 0.80 mm, urosome 0.30 mm. Bodyrelatively slender, smaller compared with that of the female(Fig. 5D). Fourth pedigerous somite as wide as succeedingsomite; fused fourth and fifth pedigerous somites taperingposteriorly, symmetrical. Rostrum strong, subtriangular,visible in lateral view (Fig. 8A). Urosome relatively short,representing 23% of total body length. Urosome symmet-rical, five-segmented, only four visible in lateral view. Firsturosomite small, telescoped into posterior somite ofprosome; second somite symmetrical, with low ventralprotuberance. Relative lengths of urosomites as: 13: 15: 17:27: 28 ¼ 100 (Fig. 5). Caudal rami as long as anal somite,symmetrical; caudal seta V symmetrical on both sides.Armature of caudal rami as in female.

Left antennule as in female. Right antennule slightlyshorter than left, with 23 free segments (Figs. 6B-D),geniculation between segments 13 and 14. Armature asfollows: 1(1), 2(2þ ae), 3(1), 4(1þ ae), 5(2), 6(2þ ae), 7(2),8(2), 9(2), 10(2þ ae), 11-12(1þ sp), 13(2þ ae), 14(2), 15(2þ ae), 16(2), 17(2þ ae), 18(1), 19(1), 20(2þ ae), 21(4þ ae),22(2), 23(5þ ae). Longest setae on segments 2, 4, 8, 10, 19,20, and 22 (Fig. 6B, C); large spines on segments 11 and 12(Fig. 6D). Mouthparts and swimming legs 1-4 as describedfor female.

Fifth leg biramous, asymmetrical (Fig. 6E, F). Both legswith coxa short, robust, unarmed, joined to reduced coxalplate. Basis of both legs strong, subquadrate, with short,slender basipodal seta inserted medially on outer margin.

Right fifth leg (Fig. 6F) reduced, with endopod 1-segmented, represented by elongated curved lamellatestructure tapering distally to blunt distal end; distal endwith subdistal pore and small terminal protuberance;endopod shorter than exopod of same leg. Exopod 2-segmented, first segment subquadrate, with biseriallyspinulated outer spiniform seta about 1/4; the length ofsuceeding segment. Second exopodal segment elongated,strongly curved inwards, armed with minute outer spiniformseta inserted on distal 1/3.

Left fifth leg (Fig. 8C, D) with endopod 1-segmented,reduced to a short, pear-shaped lobe. Exopod of left leg2-segmented, modified. First (proximal) segment short,outer distal margin with strong spiniform seta with spinuleson distal half; pore on subdistal position. Distal segment ofexopod complex, with inner proximal protuberance armedwith single short seta; three elements arise from enlargedproximal part, a slender, curved, elongated structure with

surface covered with patch of wart-like process alongexpanded subdistal surface (arrowed in Fig. 8C); secondelement represented by large rounded outer lobe withspiniform process on outer margin, process adjacent to distalrounded lobe with symmetrical, parallel membrane-likeornamentations on its surface (Fig. 8D). Third elementrepresented by sac-like subterminal hyaline, irregularstructure (Fig. 8D).

Etymology.—This species was named by using the adjec-tive verrucosus (from the Latin term verruca ¼ wart) infeminine gender to make reference to the wart-like ornamentpresent on the distal element of the left fifth leg of the male.

Remarks.—At first glance, the specimens examined herewere not clearly assignable to Ridgewayiidae because of themoderate expression of the asymmetrical insertion of boththe third exopodal segment and the expansion of the secondsegment of the female fifth leg. However, the new genus hasother important affinities with most ridgewayiids (3 outerspines on third exopod of legs 3 and 4, 26-segmentedantennules, primitive mouthparts) and particularly withRidgewayia (rostrum type, structure of male fifth legs withreduced endopods, modified exopod of first legs), Bratt-stromia (modified maxillipedal setae), and Stargatia (spineson middle segments of male right antennule) were de-terminant to decide the inclusion of these specimens withinRidgewayiidae.

The new genus can be distinguished from other genera ofthe family by a unique combination of characters. A firstattempt was made to match the characters of these speci-mens with those presented in different comparative mor-phological analyses and identification keys. For instance,when following the key for the identification of fourridgewayiid genera (Placocalanus, Exumella, Brattstromia,Ridgewayia) published by Ohtsuka et al. (1996), the newgenus does not match any of these options because it hasa strong non-bifurcated rostrum without filaments plusa maxilliped bearing long, modified setae. The characters ofthe new genus diverge also from the comparative analysisof the morphology of the swimming legs presented byFosshagen and Iliffe (1998) in reference to these four generaplus Exumellina. In this respect, Hondurella gen.nov. has noprocesses on the basis of the first swimming leg; suchprocesses are present in Brattstromia and Robpalmeria(Fosshagen and Iliffe, 2003). Most importantly, Hondurellahas a modified exopod, with long spiniform processes on thesecond segment, plus modified spines on the second andthird segments. No other of these five genera have thispattern.

Recently, Fosshagen and Iliffe (2003) described threenew genera of the Ridgewayiidae (Stargatia, Robpalmeria,Normancavia), thus increasing the number of genera. Thenew genus Hondurella differs from these three otherrecently described taxa by having a simple, strong rostrumwith no rostral filaments; Robpalmeria has a bifurcatedrostrum and a narrow rostrum with filaments, respectively.Also, there is a set of modified setae on the mandibularendopod and maxillules in Stargatia vs. a normal conditionin Hondurella gen. nov, and an unmodified first leg in thethree genera vs. a modified exopod in the new genus.


Overall, there are several additional characters inHondurella gen. nov. that are relevant to recognize it asa new genus. It has a reduced number of setae on theendopod (7), versus a condition of 9 elements present inBrattstromia, Stargatia, Robpalmeria, Normancavia, Ridge-wayia, Exumella, and Exumellina. The only other genussharing this reduced armature pattern is Placocalanus, butthe first leg endopod has a quite different structure (seeFosshagen, 1970). The structure of the exopodal ramus ofthe female fifth legs, showing a relatively wider articulationwith the second and a reduced outer expansion of the secondexopodal segment differs from most other ridgewayiidgenera (Fosshagen, 1970; Fosshagen and Iliffe, 1991, 1998,2003); only the genus Stargatia shows a similar insertionpattern but with a different armature (Fosshagen and Iliffe,2003). The number of outer spines on the third exopod oflegs 3 and 4 is 3 in the new genus, a character shared withmost genera except for Exumellina and Stargatia, both with2 outer spines on these legs. Conversely, the number ofspines on the third exopod of the fifth legs is reduced inHondurella gen. nov. (2 spines) versus a set of 3 in all otherknown genera.

The most important generic character in the female ofHondurella gen. nov. is the development of the fifth legendopod; it is reduced, one-segmented, represented by anunarmed elongate structure. The other ridgewayiid generahave different patterns (3-segmented endopods in Stargatia,Robpalmeira, Exumella, Exumellina, Brattstromia, andsome species of Ridgewayia; 2-segmented endopods insome Ridgewayia (see Wilson, 1958; Humes and Smith,1974); 1 segmented, armed endopod in Placocalanus, andlack of endopod in Normancavia) (Fosshagen, 1970;Ohtsuka et al., 1996; Fosshagen and Iliffe, 1991, 1998,2003). Also, the third exopodal segment has an armatureformula (II, I, 4) that diverges from the other ridgewayiidgenera: II, II, 4 in Stargatia, Placocalanus, Brattstromia,and Ridgewayia; II, II, 3 in Exumella, Exumellina, andRobpalmeria; II,II, 2 in Normancavia.

The male right antennule of Hondurella has two strongspines on the middle section of the antennule, each on freesegments 11 and 12 (see Fig. 6B); this character is absent inRidgewayia and is shared only with Stargatia (spines onsegments 13 and 14) (Fosshagen and Iliffe, 2003). The malefifth leg of Hondurella has additional distinguishing charac-ters. The right leg shows a reduced exopod with 2 segmentsand a reduced endopod. The left leg endopod is alsoreduced; the 2-segmented exopod bears a highly modifieddistal segment. A similar pattern can be found also inRidgewayia (see Wilson, 1958). The new genus differs fromRidgewayia in having modified setae on the maxilliped (seeFig. 4B), a feature not present in any known species of thisgenus (Wilson, 1958; Ohtsuka et al., 1996) but shared onlywith Brattstromia (see Fosshagen and Iliffe, 1991).

The unique combination of characters present in Hondur-ella gen. nov. seems to be relevant enough to erect a newgeneric name to contain the species described herein.

DISCUSSION

The new ridgewayiid genus Hondurella has some primitivecharacters, mainly in the antennule segmentation and

mouthparts armature, i.e., mandible endopod proximalsegment with 4 setae, distal with 9 setae; maxillule exopodwith 11 setae; maxillar endopod 3-segmented, third segmentwith 4 setae. This is in agreement with the general profile ofthe ridgewayiids as primitive forms.

It is generally accepted that anchialine calanoids, in-cluding Epacteriscidae and Ridgewayiidae represent old,Tethyian biogeographic patterns. It has been suggested(Suarez-Morales and Iliffe, 2005) that the anchialinecopepod fauna of the Caribbean was among the earliestisolated systems in the Northwestern Tropical Atlantic andthus indicates a relatively old biogeographic origin.

The geological development of the Caribbean regionrepresents a complex process (Iturralde-Vinent and McPhee,1999) by which marine ancestors of these taxa had theopportunity of colonizing cave habitats at different times(Boxshall and Jaume, 2000). These forms were isolated andevolved in different conditions. This concept provides anexplanation of the presumed high endemism of bothEpacteriscidae and Ridgewayiidae in geographically closeareas: seven ridgewayiid genera coexist in the Bahamas(Fosshagen and Iliffe, 2003); the epacteriscid fauna of theYucatan Peninsula differ from that known in the adjacentcoast of Belize (see Suarez-Morales et al., 2006).

The coastline of Honduras corresponds to the ChortisBlock, with a similar geological development as that of theMayan Block, to which the Yucatan Peninsula (YP) belongs(Donnelly et al., 1990). As speculated for the YP anchialinefauna (Suarez-Morales and Iliffe, 2005; Suarez-Moraleset al., 2006), and by the geological origin of Utila (Pliocene),it was during the late Pliocene that the marine ancestors ofthese forms colonized the caves and remained relativelyisolated in these systems. In the Caribbean region, the suc-cessive marine transgressions and regressions promoteddispersal and isolation/stranding processes, respectively. Itis speculated that, as other anchialine forms, ancestors ofHondurella were isolated by the overlying freshwater lensduring the marine regressions, when continental freshwaterdeluged these cave systems and formed a strong haloclinethat acted as a physical barrier.

So far, the Bahamas have the most diversified ridge-wayiid fauna (Fosshagen and Iliffe, 2003). The westernCaribbean, including Belize and the eastern coast of the YP,has been revealed recently as a potentially rich area for bothepacteriscids and ridgewayiids (Suarez-Morales and Iliffe,2005; Suarez-Morales et al., 2006), but large areas ofCentral and South America remain unstudied for these taxa.

Most species of this family have been known to occurin shallow marine waters as hyperbenthic forms (Boxshalland Halsey, 2004). Some genera live in marine caves,Placocalanus dwells in hyperbenthic communities outsidecaves, and species of Exumella can be found in anchialinesystems and also as inhabitants of shallow coastal waters.Most of the known genera: Brattstromia, Exumellina,Normancavia, Robpalmeria, Stargatia, and now Hondurellanew genus, have been found in anchialine waters only, thusconfirming the association of ridgewayiids to these in-teresting systems.

The structure of the mouthparts is a valuable data inspeculating about the feeding habits of these cave-dwelling


organisms; species of Ridgewayia, Brattstromia, Exumel-lina, and Stargatia were deemed as particle feeders byFosshagen and Iliffe (2003) because of the presence ofslender, elongate setae on mandibles and maxillules. Otherridgewayiids, armed with strong, modified seta on themaxilliped (Exumella, Normancavia) were considered asraptorial feeders. Aside the branched maxillipedal setae,Hondurella has normally developed mouthparts, with long,slender setae and a mandible blade with low teeth. Ingeneral, this pattern suggests that this species is a particle-feeder. The analysis of gut contents, with conglomerates oforganic particles in all cases, and no indications ofcarnivorous activity, seem to support this statement.Furthermore, the finding of relatively large numbers of thisspecies in the net may indicate that it is not a predator; it alsosuggests aggregative behavior.

ACKNOWLEDGEMENTS

This work was developed partly as a result of a sabbatical leave of the firstauthor (ES-M) to the National Museum of Natural History-SmithsonianInstitution, Washington, D.C. supported by CONACYT (Mexico) and theCIES Fulbright Program. We appreciate the comments from Chad Walteron these specimens and access to valuable literature. Audun Fosshagen,University of Bergen, Norway, kindly commented on an earlier version ofthis work and sent information about other ridgewayiids in process ofdescription. Susan Brenan and Scott Whittaker, SEM Laboratory at theNMNH-SI in Washington, D.C., kindly prepared the specimens and guidedour SEM examination of the new genus.

REFERENCES

Boxshall, G. A., and D. Jaume. 2000. Making waves: the repeatedcolonization of freshwater by copepod crustaceans. Advances inEcological Research 31: 61-79.

———, and S. H. Halsey. 2004. An Introduction to Copepod Diversity.Vol. I. The Ray Society, 166 London. 421 pp.

Donnelly, T. W., G. S. Horne, R. C. Finch, and E. Lopez-Ramos. 1990.Northern Central America: the Maya and Chortis Blocks, pp. 37-76. In,G. Dengo and J. E. Case (eds.), The Geology of North America. Vol. H.The Caribbean Region. Geological Society of America. Boulder.

Fosshagen, A. 1970. Ridgewayia (Copepoda, Calanoida) and two newgenera of calanoids from the Bahamas. Sarsia 44: 25-58.

———, and T. M. Iliffe. 1985. Two new genera of Calanoida and a neworder of Copepoda, Platycopioida, from marine caves on Bermuda.Sarsia 70: 345-358.

———, and ———. 1991. A new genus of calanoid copepod from ananchialine cave in Belize. Bulletin of the Plankton Society of Japan,Special Volume (1991): 339-346.

———, and ———. 1998. A new genus of the Ridgewayiidae (Copepdoa,Calanoida) from an anchialine cave in the Bahamas. Journal of MarineSystems 15: 373-380.

———, and ———. 2003. Three new genera of Ridgewayiidae(Copepoda, Calanoida) from anchialine caves in the Bahamas. Sarsia88: 16-35.

Humes, A. G., and W. L. Smith. 1974. Ridgewayia fosshageni n. sp.(Copepoda; Calanoida) associated with an actiniarian in Panama, withobservations on the nature of the association. Caribbean Journal ofScience 14: 125-139.

Huys, R., and G. A. Boxshall. 1991. Copepod Evolution. The Ray Society,159 London. 468 pp.

Iturralde-Vinent, M. A., and R. D. F. MacPhee. 1999. Paleogeography ofthe Caribbean region: implications for Cenozoic biogeography. Bulle-tin of the American Museum of Natural History 238: 1-95.

Ohtsuka, S., A. Fosshagen, and H. Y. Soh. 1996. Three new species of thedemersal calanoid copepod Placocalanus (Ridgewayiidae) from Okina-wa, Southern Japan. Sarsia 81: 247-263.

———, T. Kase, and G. A. Boxshall. 2000. A new species of Ridgewayia(Copepoda: Calanoida) from a submarine cave in Palau, westernPacific. Species Diversity 5: 201-213.

Suarez-Morales, E., and T. M. Iliffe. 2005. A new Exumella Fosshagen(Crustacea: Copepoda: Ridgewayiidae) from anchialine waters of thewestern Caribbean, with comments on regional biogeography. Bulletinof Marine Science 77: 409-423.

———, F. Ferrari, and T. M. Iliffe. 2006. A new epacteriscid copepod(Calanoida: Epacteriscidae) from the Yucatan Peninsula, Mexico, withcomments on the biogeography of the family. Proceedings of theBiological Society of Washington 119: 222-238.

Thompson, I. C., and A. Scott. 1903. Report on the Copepoda collected byProfessor Herdman, at Ceylon, in 1902. Reports of the Government ofCeylon Pearl Oyster Fisheries, Supplementary Reports 7: 227-307.

Wilson, M. S. 1958. A review of the copepod genus Ridgewayia(Calanoida) with descriptions of new species from the Dry Tortugas,Florida. Proceedings of the United States National Museum 108: 137-179.

RECEIVED: 20 February 2006.ACCEPTED: 27 July 2006.


A NEW GENUS OF RIDGEWAYIIDAE (COPEPODA: …plesiomorphic characters, thus conﬁrming the primitive...

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