A new species of Caligus (Copepoda, Siphonostomatoida) from the plankton of the Caribbean coast of Venezuela with a key to species

Abstract During a survey of the zooplankton community of Bahía Amuay, Venezuelan Caribbean, specimens of an undescribed species of Caligus Müller were collected. It resembles Caligus xystercus Cressey and Caligus ocyurus Cressey, both known only from the Caribbean Sea. The new species can be distinguished from these and other congeners by a combination of characters including the armature of legs 1 and 4, but mainly by its unique female genital complex. This is the first species of Caligus described from Venezuela. The species is described in full and a key to the species of the genus recorded in Venezuela is provided.


introduction
The siphonostomatoid copepods of the genus Caligus Müller, 1785 are one of the most diverse and representative crustacean parasites of teleost fish (Boxshall and Halsey 2004;Ho and Lin 2004). They are usually recorded as ectoparasitic forms attached to the hosts, but in many cases they can be found in the plankton (Venmathi Maran and Ohtsuka 2008). Records of parasitic copepods of Venezuelan marine teleosts are relatively scarce (Luque and Poulin 2007). This is particularly true in the Caribbean Sea, a region in which the parasitological research is lagging despite the high number of parasite species harbored by Caribbean fish (Bunkley- Williams and Williams 1994;Luque and Poulin 2007). Previous surveys of the caligid fauna of Venezuela are relatively scarce and up to 10 species of Caligus have been recorded from this country (Ho and Bashirullah 1977;Legarde 1989;Williams and Bunkley-Williams 1996;Díaz Díaz 2000;Zambrano et al. 2003).
A recent (February 21-24, 2012) biological survey of the planktonic fauna was carried out at the Bay of Amuay, a coastal system on the northern coast of Venezuelan Caribbean coast, which is also an important oil extraction site with pollution problems (Pomares Ferraz et al. 2008). Specimens of the copepod genus Caligus were recorded in these samples. These individuals represent a new species which is described here and compared with its closest congeners. An identification key to the species of Caligus recorded from Venezuela is also provided.

Material and methods
Adult female and male individuals of a caligid copepod of the genus Caligus were recovered from plankton samples obtained from Bahía Norte, a shallow coastal system which is part of the Bay of Amuay (11°46'32"N, 70°13'51"W), in the northwestern coast of Venezuela. The plankton fauna from this area was surveyed during several days (February 21-24, 2011) by performing horizontal hauls with a standard plankton net (0.5 mm mesh size, 0.3 m mouth diameter). Specimens were fixed shortly after collection in 70% ethanol. Specimens of Caligus were sorted from these samples and processed for identification by transferring them to glycerol and then pure glycerine. Drawings were prepared using a camera lucida mounted on an E-200 Nikon compound microscope. Terminology of the body parts and appendages follows Ho and Lin (2004). Type specimens were deposited in the collection of Zooplankton held at El Colegio de la Frontera Sur (ECOSUR), Unidad Chetumal (ECO-CHZ), Quintana Roo, Mexico. Sternal furca (Fig. 1B) tines slightly incurved, membranous on outer margin and longer than base. Leg 1 ( Fig. 2A) coxa with patch of very fine spinules in addition to long setulated outer seta and short inner seta. Mammiliform papilla on distal position of seg-ment. First exopodal segment with row of short hair-like elements. Last exopod segment bearing 3 medial pinnate setae and 2 terminal spines, each with accessory process, with additional medial distal seta; usual small seta on outer terminal corner not seen (Fig. 2B). Leg 2 (Fig. 2C) coxa small, with long plumose seta on inner margin and setulebearing papilla on middle-outer surface. Basipodite robust, with small seta on outer edge and a setule-bearing papilla on middle inner margin. First exopodal segment bearing spine reaching across second segment to proximal margin of third segment; second segment with much shorter spine recurved on outer margin, spine reaching to middle of last segment. Distal segment with short spine on outer margin plus one short setule. Terminal spine sclerotized, articulated, as long as distal segment (Fig. 2D). All setae on medial margins of all segments pinnate.
Leg 3 (Fig. 2E) exopod first segment with stout, slightly recurved, terminal spine with thin flange on outer lateral margin nearly reaching to third segment; setae as in figure and typical of genus; second endopodal segment with single inner pinnate seta, second segment with 6 pinnate setae.
Leg 4 (Figs 2 F,G) uniramous, brachiform; exopod 2-segmented. Protopod with short plumose seta in distal outer margin. First exopodal segment with terminal seta not reaching base of middle lateral seta of last segment. Second exopodal segment bearing 3 unequally long setae, outermost shortest and medial longest; each with pecten at base.
Description of male. Body (Fig. 3A) larger than female, 3.1 mm long excluding setae on caudal rami. Cephalothoracic shield roughly ovoid in shape, 1.78 mm long and 1.35 mm wide (excluding marginal hyaline membranes: 0.07 mm). Frontal plates well developed and carrying moderately large lunules separated by 1.5 the diameter of a lunule; free margin of thoracic zone projecting slightly beyond tips of lateral zones; sinuses moderately deep. Fourth pediger separated from genital complex, roughly hexagonal in shape, about twice longer than wide. Genital somite subrectangular. Abdomen 1mm long, represented by two somites; proximal somite subquadrate, anal somite distinctly longer than wide. Caudal ramus subrectangular, slightly longer than wide, bearing 3 short (one inner, two outer) setae, and 3 long terminal setae. Inner margin naked.
Leg 5 (Fig. 3J) located on middle of lateral margin of genital complex, represented by two papillae, one (proximalmost) armed with short seta and the other with two short, slender setae. Leg 6 ( Fig. 3J) represented by single papilla armed with two short, pinnate seta.
Etymology. The new species is named after Dr. Evelyn Zoppi de Roa, an esteemed Venezuelan researcher who pioneered much of the zooplankton research in this country and has lead new generations of planktologists during her long career.
Remarks. This species is closely related to other two species of Caligus described from the Northwestern tropical Atlantic: Caligus ocyurus Cressey, 1991and C. xystercus Cressey, 1991, they all share a longer than wide genital complex, a relatively short abdomen, a similar structure and armature of legs 1 with three inner setae on the last segment and four distal elements, two of them with accessory spines. They have also a fourth leg armed with 5 spines; the three terminal spiniform elements are of different lengths, the outermost being longest. Cressey (1991) distinguished C. ocyurus from C. xystercus by the proportions of the caudal rami and the abdomen; these structures are not longer than wide in C. xystercus, as it occurs in C. ocyurus. Also, the postantennal process of C. ocyurus is much stouter and broader at the tip than in C. xystercus. The new species has a postantennal process as in C. xystercus, not spatulate or particularly wide distally as in C. ocyurus. In C. xystercus the caudal rami are equally long as wide and in C. ocyurus they are twice as long as they are wide, whereas they are 1.5 times longer than wide in C. evelynae. The new species shares with C. ocyurus a claw-like terminal segment of the male antenna, a relatively short outermost distal seta of the second exopodal segment of leg 1, and the female is smaller than the male. The new species can be readily distinguished from C. ocyurus by the shape of the cephalothoracic shield, which is clearly ellipsoidal with curved lateral margins in C. evelynae sp. n. (see Fig. 1A) and it is rectangular with straight lateral margins in C. ocyurus (Cressey 1991, fig . 127). In C. evelynae sp. n., the basipodal segment of leg 1 lacks a large medial protuberance present in C. ocyurus (Cressey 1991 , fig. 131). The sternal furca is clearly different in both species; tines are straight, relatively long, widely separated, and distally tapered in C. ocyurus (Cressey 1991, fig. 130) whereas they are shorter, more robust, incurved and distally rounded in C. evelynae. The maxillule is slender in the new species vs. a stronger, more robust condition in C. ocyurus (Cressey 1991 , fig. 129c). The armature of leg 4 is different; distal elements differ in length and proportion in both species; the size of the short outermost element is about 1/3 the length of the medial element, which in turn is about half the length of the innermost element; this pattern differs in C. evelynae sp. n., in which the shortest element is about half the length of the medial one and this is about 0.75 times as long as the innermost element. In C. ocyurus the male genital somite is as long as wide, with protuberant lateral margins (Cressey 1991, fig. 135), whereas in the new species this somite is longer than wide with weakly produced lateral margins. The male antenna is described as bifid by Cressey (1991) and it is not bifid in the new species. Also, the size and position of the pads differ in the new species (see Fig. 3B vs Cressey 1991, fig . 136); particularly, the new species has a longitudinal adhesion pad along the inner margin whereas this margin is smooth in C. ocyurus (Cressey 1991 , fig. 136).
Following Cressey's (1991) criteria, these three species can be separated from the other known Caligus species of the Gulf of Mexico and Caribbean Sea by the following characters. The structure and armature of the exopod of the fourth leg with a 2-segmented exopod bearing 5 spines is a character shared by at least 11 species of the genus in this region (Cressey 1991). This group of species can be distinguished from C. asperimanus Pearse, 1951, C. berychis Wilson, 1935, C. bonito Wilson, 1905, C. haemulonis Krøyer, 1863, C. mutabilis Wilson, 1905, and C. suffuscus Wilson, 1913 in having short setules along the outer margin of the second leg endopod instead of patches of spinules. This group of species can be distinguished from the remaining 6 other species with setules on the second leg endopodal segments as follows: the female C. chelifer Wilson, 1905 has a 2-segmented abdomen and very short lateral setae on the exopod of leg 1, vs. a 1-segmented female abdomen and relatively longer setae on the leg 1 exopod; C. praetextus Bere, 1936 bears unique "hooded" distal spines on the exopod of leg 1, and two of the terminal elements of leg 4 are equally long, about half the length of the inner element, C. afurcatus Wilson, 1913 has also two equal terminal elements on leg 4, reduced caudal rami, relatively short lateral seta of the distal exopodal segment of leg 1, a reduced sternal furca, and a relatively long outer spine on the first exopodal segment of leg 2; in C. rufimaculatus Wilson, 1905 the sternal furca tines are clearly spatulate, with an enlarged distal margin, caudal rami only slightly longer than wide, C. productus Dana, 1852 lacks medial lateral setae on leg 1 and has no accessory spines on leg 1 exopod.
Overall, the main character distinguishing the new species, C. evelynae, is the peculiarly strong, irregular undulation of the genital complex; another species with a genital complex bearing undulated margins reported in the region is C. undulatus Shen and Li, 1959 (Suárez-Morales et al. in press), but in this species the first leg has a different armature, with four distal elements, the genital complex is trapezoidal vs. a subrectangular shape in the new species; the abdomen is shorter in C. evelynae (30% length of genital complex), whereas in C. undulatus the abdomen is clearly longer (67%). Also, undulation in C. undulatus is relatively shallow and regular, contrasting with the pattern found in C. evelynae. This species was originally described from specimens in plankton samples from China (Shen and Li 1959) and has been recorded only from the water column, hosts remain unknown (Venmathi Maran and Ohtsuka 2008). Other species of Caligus with an undulate or rugose genital complex are C. lobodes (Wilson, 1911) and C. rugosus Shiino, 1959. The new species differs from the former in the body shape, which is quite different, the genital complex is trapezoidal and the abdomen is as wide as the genital complex; lobes are symmetrical, lunules are widely separated from each other and it has a forked maxillular process (Wilson 1911), thus differing from the pattern described for C. evelynae. In C. rugosus the genital complex is also irregularly lobulated but it is produced posteriorly, forming large posterolateral processes which are absent in the new species. Also, the sternal furca has very wide, wing-like tines (Shiino 1959, fig. 1G) vs. regular, slender tines in C. evelynae.
It is interesting to point out that these three very similar species of Caligus (C. xystercus, C. ocyurus, C. evelynae) appear to be restricted to the Northwestern Atlantic (Cressey 1991) following the pattern described by Ho and Lin (2003) in reference to another group of Old World species of Caligus with a well-defined geographic affinity. This criterion motivated their revision of New World records of these Old World species and the naming of a new species from the Caribbean Sea, which was formerly identified as C. epinepheli Yamaguti, 1936by Cressey (1991. Hence, it appears that this group of related species from the Gulf and the Caribbean basins, in which we include also C. rufimaculatus, are probably restricted to this region. Based on the available data, there are about 31 nominal species of Caligus known in the Gulf of Mexico and the Caribbean (Wilson 1913;Cressey 1991;Bunkley-Williams and Williams 1994;Álvarez-León 2009;Suárez-Morales et al. 1998. Only a few of them are known to be restricted to this geographic region, including C. xystercus, C. ocyurus, C. kabatae Cressey, 1991, C. pomacentrus Cressey, 1991, C. cresseyi Ho and Lin, 2003, and probably the new species, C. evelynae. More taxonomical surveys are yet to be developed in order to reveal more of the potentially highly diverse caligid fauna in the region.