A new species of Halicyclops (Copepoda, Cyclopoida, Cyclopidae) from a lagoon system of the Caribbean coast of Colombia

Abstract Plankton samples obtained from the lagoon system Laguna Navío Quebrado, in northern Colombia, yielded male and female specimens of an undescribed cyclopoid copepod of the genus Halicyclops. The new species belongs to the highly diverse and widely distributed thermophilus-complex. It closely resembles Halicyclops clarkei Herbst, 1982 from Louisiana and Halicyclops bowmani Rocha & Iliffe, 1993 from Bermuda. These species share the same armature of P1-P4EXP3, with a 3443 spine formula and the terminal antennary segment with 5 setae. However, Halicyclops gaviriai sp. n. can be separated from both Halicyclops clarkei and Halicyclops bowmani by the morphology of the anal pseudoperculum, the proportions of the fourth antennulary segment, the length of the inner basipodal spine of P1, the P1EXP/inner basipodal spine inner length ratio and the length/width ratio of the caudal rami. This is the third species of Halicyclops recorded from Colombia and the first one described from this country. With the addition of Halicyclops gaviriai sp. n., the number of species of Halicyclops known from the Neotropics increases to 19. The regional diversity of the genus is probably underestimated.


Introduction
The cyclopoid copepod genus Halicyclops is the most speciose in the subfamily Halicyclopinae; currently, it is known to contain 111 species and subspecies (Boxshall 2014) and is in need of revision. Members of this genus are cosmopolitan and planktonic forms (Chang 2012;Ueda and Nagai 2012), inhabiting chiefly coastal brackish water habitats, but some species can be found in freshwater habitats (Rocha 1995;Bazilevich and Kaftannikova 1970;Defaye and Dussart 1988;Fuentes-Reinés and Zoppi 2013).
In the Americas, Brazil and the United States are the countries with most records of Halicyclops (Wilson 1958;Herbst 1977Herbst , 1982Rocha 1983, 1984, 1991, 1995, Rocha and Hakenkamp 1993. According to Rocha et al. (1998) there are about 17 species of Halicyclops recorded in the Caribbean region and this figure remained stable until the recent description of a new species from Argentina (Menu-Marque and Sorarrain 2007). In Colombia, the knowledge about this genus is still very limited; up to now, only two species, H. venezuelaensis Lindberg, 1954 andH. exiguus Kiefer, 1934 have been reported from two Caribbean localities of Colombia: Ciénaga Grande de Santa Marta, Magdalena and Laguna Navío Quebrado, La Guajira, respectively (Fuentes-Reinés et al. 2013, Fuentes-Reinés and Suárez-Morales unpubl. data). The few reports of Halicyclops in Colombia together with the high potential diversity of the genus in the area emphasizes the importance and necessity of intensifying the biological research in fresh and brackish water body in the country to improve our knowledge about the copepod fauna living in these environments. During a survey of the plankton community of the lagoonal system of Laguna Navío Quebrado, in the Colombian coast of the Caribbean, male and female specimens of an undescribed species of Halicyclops were collected. The aim of this paper is to describe this new species and compare it with its closest congeners.

Methods
Plankton samples were taken monthly from the Laguna Navío Quebrado, Colombia (11°25'N, 73°5'W) between April and December 2012, mainly in the littoral areas with vegetation (macrophytes and mangrove) but also from open water in areas close to oyster banks. Water salinity was measured with a WTW 3111 conductivity meter. Water samples were collected using a bucket of 25 L at both vegetation areas and shallow open water. Samples were filtered with a zooplankton net (45 μm) and preserved in 70% ethanol. Copepods were sorted from the original samples and then processed for taxonomical identification. Dissected specimens and appendages were mounted in glycerine and sealed with Canada balsam. Drawings were made with the aid of a camera lucida mounted on an Olympus BX51 compound microscope equipped with Nomarski DIC. The specimens were measured in lateral position, from the anterior end of the rostral area to the posterior margin of the caudal ramus. The specimens examined were deposited at the Museo de Colecciones Biológicas at the Universidad del Atlántico (UARC), Colombia and in the Collection of Zooplankton (ECO-CHZ) held at El Colegio de la Frontera Sur (ECOSUR), Chetumal, Mexico. Morphological terminology follows Huys and Boxshall (1991). The following abbreviations are used in the description: P1-P6= first to sixth swimming legs, EXP= exopod, ENP= endopod. Male allotype (UARC394Z), both partially dissected. Paratypes: ten females and four males, undissected, ethanol-preserved, vial (UARC395Z), plus one dissected female, slides (UARC399Z-403Z) and one dissected male (UARC397Z). Three adult females from same locality and date, two of them undissected, ethanol-preserved, in vial, one mounted on slide (ECO-CHZ-09267).
Antenna consisting of 4 segments, coxa reduced and unarmed, basis with 2 setae at inner corner; seta representing EXP present. ENP two-segmented. Proximal endopodal segment with a seta on middle inner margin. Terminal endopodal segment about 1.4 times as long as preceding segment armed with 5 inner setae and 7 apical setae plus short spinule on proximal outer margin. Length/wide ratio of second segment about 2.3 (Fig. 1E).
Mandible with well-developed coxal gnathobase, armed with 7 teeth plus outermost dorsal pinnate seta. Palp reduced, represented by 2 naked setae inserted on small protuberance, one seta about 1/3 times as long as the other one ( Fig. 1F) Maxillule with praecoxal arthrite bearing four strong tooth-like spines distally, inner spine strongest, with two proximal subequal setae, inner surface with two robust setal elements and one regular seta. Palp two-segmented, basis with 4 setae, endopodite represented by single oval-shaped segment, armed with three subequal, lightly setulated setae (Fig. 1G).
P5 exopod subrectangular (Fig. 3E), about 1.56 times as long as wide, armed with 3 spines, all of them shorter than segment, plus one flexible seta 1.2 times as long as segment; relative length of elements from inner to outer margin as follows 0.66, 1.0; 0.46; 0.6.
Etymology. The species is named after Dr. Santiago Gaviria for his work on Colombian copepods and his leadership in the formation of new generations of planktologists.
Remarks. Halicyclops gaviriai sp. n. is assigned to the group of species "B" of Halicyclops with a 3443 spine formula; this is the most diverse group containing 74 species (see Pesce 2014). One of its subgroups, including approximately 15 species (Pesce 2014) is the thermophilus-complex, proposed by Herbst (1983). Species in this group share the presence of a chitinous blunt hook-like process on each side of the genital double-somite, but in H. gaviriai this process is reduced or absent. Other characters related to this group include: inner distal margin of the basis of leg 1 devoid of setae, thus diverging from H. gaviriai sp. n. with a well-developed inner basipodal spine. Two characters of the thermophilus group present in our specimens are: intercoxal sclerite of P1-P4 naked, and regular, unmodified setae on P4 EXP2-3. Because of the absence of the main group characters, the new species is not assigned to the thermophiluscomplex. In Colombia, only one species of the thermophilus group has been hitherto recorded: H. venezuelaensis Lindberg, 1954. Among the species of Halicyclops reported from the Caribbean region and adjacent areas (Rocha et al. 1998), H. gaviriai sp. n. closely resembles H. clarkei Herbst, 1982 described from Louisiana andH. bowmani Rocha &Iliffe, 1993 from Bermuda. Both of them lack strong processes on the genital double-somite and have a P1 with a strong inner basipodal spine (Herbst 1982;Rocha and Iliffe 1993;Pesce 2014). When the most recent key to the Neotropical species of Halicyclops (Rocha et al. 1998) is followed, our specimens from Colombia key down to a couplet leading to these two species (H. clarkei, H. bowmani). They share the same spine formula of P1-P4EXP3 (3443), the P4EXP3 with 3 spines on the outer margin, and the terminal antennulary segment with 5 lateral setae. The female fifth legs of these species are also very similar (Herbst 1982;Rocha 1991). However, H. gaviriai sp. n. can be separated from both H. clarkei and H. bowmani by differences in several characters. In H. clarkei the integumental windows of the genital double-somite are rounded and relatively small (Herbst 1982, fig. 15) whereas they are oblong and larger in the new species (Fig. 3A). The morphology and ornamentation of the anal pseudoperculum has been regarded of taxonomical value to distinguish species in this group (Rocha and Iliffe 1993;Pesce  0-1 1-I I-0, I-1,III-1,4 0-1,0-1,II-2,2 Leg 2 0-1 0-0 I-1,I-1,III-1-1,4 0-1,0-2, III-3 Leg 3 0-1 1-0 I-1,I-1,III-I-1,4 0-1,0-2, III-3 Leg 4 0-1 1-0 I-1, I-1, II-I1-4 0-1,0-2, I-II-II 2014). This structure is slightly curved and bears tiny denticles along the free margin in H. clarkei (Herbst 1982, fig. 16), it is strongly developed and coarsely serrate in H. bowmani (Rocha and Illife 1993, fig. 27), and it has shallow, irregular indentations, and is slightly curved in the new species (Fig. 3B). The length/width ratio of the fourth antennulary segment differs in these species, it is much shorter in H. gaviriai (ratio = 1.7) vs. 2.5 in H. bowmani (Rocha and Iliffe 1993) and 2.7 in H. clarkei (Herbst 1982 , fig. 18). Also, in H. clarkei the inner basipodal spine of P1 is long, slender, it reaches half of P1ENP3 (Herbst 1982, fig. 19), in H. bowmani this spine is more robust and shorter, it doesn't reach the distal margin of P1ENP2 (Rocha and Illife 1993, fig. 29), whereas in H. gaviriai this spine reaches the distal margin of P1ENP2 ( Fig. 2A). The length ratio P1EXP/basipodal spine is about 2.0 in H. bowmani (Rocha and Iliffe 1993, fig. 29), 1.42 in H. clarkei (Herbst 1982, fig . 19), and 1.63 in H. gaviriai.
The armature details of P4ENP3 shows some additional differences among these species; this segment is armed with 4 spines and one spiniform, distally serrate seta in both H. clarkei (Herbst 1982, fig. 22;Rocha 1991, fig. 10) and H. gaviriai sp. n., while in H. bowmani the armature consists of 3 spines and 2 stout, plumose setae (Rocha and Iliffe 1993, fig. 31). Also, in H. clarkei the inner apical spine of P4ENP3 is as long as the segment (Herbst 1982, fig. 22;Rocha and Hakenkamp 1993), whereas in both our specimens from Colombia and in H. bowmani (Rocha and Iliffe, 1993, fig. 31) this spine is 1.25 times as long as the segment (Fig. 2D, E). The proportions of the caudal ramus have some variation among these species, the length/width ratio is about1.5 in H. clarkei, 1.3 in H. bowmani, and 1.2 in H. gaviriai sp. n. The inner/outer apical caudal setae length ratio is 1.8 in both the new species and in H. bowmani (Rocha and Iliffe 1993, fig. 28) vs. 2.3 in H. clarkei (Herbst 1982, fig. 14). The body size of these species show some additional differences: measuring 560-602 μm, the female of the new species H. gaviriai is larger than those of H. bowmani (500-530 μm) (Rocha and Iliffe 1993), but smaller than the females of H. clarkei (698 μm) (Herbst 1982).
The new species has also affinities with Halicyclops cf. clarkei from Panama (Rocha, 1991), but can be easily distinguished from the new species from Colombia by the armature of the female P5, in Halicyclops cf. clarkei the outermost spine is slightly shorter than the innermost and both are longer than the terminal segment (Rocha 1991, fig. 13), but in the new species the innermost spine is as long as the segment and the outermost spine is shorter than the segment (Fig. 3E). According to Rocha (1991), in both Halicyclops cf. clarkei from Panama and H. clarkei from the type locality in Louisiana the length/width ratio of the fourth antennulary segment are identical, about 2.7; this value diverges from that found in H. gaviriai (1.7). Also, in Halicyclops cf. clarkei the ENP3 of P2-P3 have the proximalmost inner seta modified as a stiff ornamented seta as the proximal seta of ENP3 of P4 (Rocha 1991, fig. 10), but in the new species these seta are unmodified, flexible elements (Fig. 2B, C). Rocha (1991) stated that the differences between the Panama specimens of H. cf. clarkei and those from the type locality in Louisiana are probably related to different species.
The male of the new species H. gaviriai differs from the male of H. clarkei in the presence of modified setae on the antennular segments 10-11, lacking in H. clarkei (Herbst 1982, fig. 25). Also, the length/width ratio of P4ENP4 is about 1.63 times as long as wide in H. gaviriai sp. n., while in H. clarkei is 1.53. The length/width ratio of P5EXP is about 1.27 in H. gaviriai sp. n., vs. 1.64 in H. clarkei (Herbst 1982, fig . 26). In H. clarkei the outer seta of P6 is clearly longer than the inner spine (Herbst 1982, fig. 27), whereas in H. gaviriai sp. n., the opposite condition occurs, the outer seta is shorter. Unfortunately, the male of H. bowmani remains unknown (Rocha and Iliffe 1993) and could not be compared with the male of the new species.
Halicyclops gaviriai sp. n. is characterized by a unique combination of characters including: 1) last antennary segment with five lateral setae, 2) length/wide ratio of same segment over than twice as long as wide, 3) fourth segment of female antennule over than twice as long as wide, 4) inner basipodal spine of P1 reaching the posterior border of the ENP2 of P1, 5) ENP3 of P4 with four serrate spines and one seta, and 6) P5 about 1.45 times as long as wide, apical seta longer than the segment.
Distribution and ecology. Halicyclops gaviriai sp. n. is currently known from a single locality only, the protected coastal system Laguna Navío Quebrado, on the Caribbean coast of Colombia. This species was recorded in both the limnetic region and the vegetation zones, being more frequent in the former habitat. This large (surface area of 10.7 km 2 ) lagoon system is a shallow water body (depth 0.3-1.1 m), whose temperature varies over the seasons in the range of 28-31 °C; pH values during sampling ranged between 7.8 and 8.3 and salinity was 28 PSU. This habitat diverges from that of one of its closest congeners, H. bowmani, a stygobitic form recorded only from an anchialine system of Bermuda (Rocha and Iliffe 1993). The known habitat of its other close congener, H. clarkei, is Lake Peigneur, a former freshwater system whose salinity drastically increased since 1980 after a failed oil drill deeply modified the system (Zio and Aven 2013). The samples examined by Herbst (1982) were obtained before this event, in 1977; he reported a low salinity range (0-5 psu) for this species. Hence, it is an intriguing question if this presumably endemic species was able to adapt to the new conditions and is still extant in the locality or adjacent areas.
The number of Neotropical species recognized by Rocha et al. (1998) was 17 and it remained stable in the region until the recent description of H. ramirezi from Argentina (Menu-Marque and Sorarrain, 2007) and the addition of this new species from Colombia, thus raising the number of known Neotropical species to 19. Furthermore, some nominal species in the literature such as H. cf. clarkei from Panama (Rocha 1991) probably represent undescribed species. The diversity of the genus in the region could be underestimated and certainly deserves further investigations.