Cymbasoma cocoense, Suárez-Morales & Morales-Ramírez, 2009

Suárez-Morales, Eduardo & Morales-Ramírez, Alvaro, 2009, New species of Monstrilloida (Crustacea: Copepoda) from the Eastern Tropical Pacific, Journal of Natural History (J. Nat. Hist.) 43 (21 - 22), pp. 1257-1271 : 1259-1264

publication ID	https://doi.org/ 10.1080/00222930902894419
publication LSID	lsid:zoobank.org:pub:2EB343F4-0486-4096-B53E-C650357406B0
persistent identifier	https://treatment.plazi.org/id/03ADD769-D422-816F-EF52-FEEF561FCC98
treatment provided by	Felipe
scientific name	Cymbasoma cocoense
status	sp. nov.

Treatment

Cymbasoma cocoense sp. nov.

( Figures 1–3 View Figure 1 View Figure 2 View Figure 3 )

Material examined

Holotype. Adult female, ethanol-preserved, undissected. Plankton collection, Chatham Bay, Isla del Coco, Costa Rica (5°33′01.58′′ N, 87°02′18.57′′ W). Specimen collected 12 November 2000 by J. Picado, permanent slide mounted in glycerine and sealed with Entellan ®, ECO-CHZ-03956. GoogleMaps

Paratypes. Two adult females, same date and locality, undissected, ethanol-preserved (ECO-CH-Z-03957). Two adult females from Wafer Bay (5°32′41.67′′ N, 87°03′23.22′′ W) GoogleMaps ,

Isla del Coco, Costa Rica, undissected, ethanol-preserved, deposited, together with original zooplankton samples, at CIMAR, San José, Costa Rica.

Description

Adult female. Total body length of holotype: 1.62 mm, range: 1.45–1.67 mm, mean: 1.56 (n = 4), measured from anterior end of cephalic somite to posterior margin of anal somite. Cephalothorax incorporating first pedigerous somite narrow, relatively long, accounting for 59.6% of total body length ( Figure 1A,B View Figure 1 ). Forehead rounded, moderately protuberant in dorsal view, anteriormost dorsal surface smooth. Ventral surface of head with pair of chitinized, rounded, nail-like processes near bases of antennules. Single pair of moderately developed nipple-like cuticular processes on ventral surface between antennule bases and oral papilla, processes surrounded and connected by field of weak transverse ridges reaching base of oral papilla. Oral papilla weakly protuberant, located close to anteriormost part of body, midventrally 0.21 of way back along cephalothorax ( Figure 2A,B View Figure 2 ). Nauplius eye present, moderately developed, ocelli relatively large, moderately pigmented, rounded, eyes separated by less than one-half eye diameter.

Antennule length 0.27 mm. Antennules relatively short, slightly shorter than 17% of total body length, and about 28% of length of cephalothorax. Antennules foursegmented, intersegmental divisions well-defined. Last antennular segment longest, representing 45% of total length of antennule; ratio of lengths of segments (proximal– distal): 10.1: 27.4: 15.9: 46.5 = 100. Armature with 0, I; 1, V; 2, I; 11, VI setae (Roman numerals) and spines (Arabic numerals) ( Figure 2C View Figure 2 ) plus two aesthetascs, both on last segment, one on proximal ventral surface, one subdistal. Following pattern described by Grygier and Ohtsuka (1995) for monstrilloid antennular armature, setae and spines on first (1), second (2d 1–2, 2v 1–3, IId) and third (3, IIIv, IIId) segments complete. Fourth segment with 4v 1,2, IVv, IVd, 4d 1,2, Vm, Vd, Vv, 5, 61, 62, 4aes, 6aes, b 1–6. Setae b 1–3 unbranched.

Incorporated first pedigerous somite and three free succeeding pedigerous somites, each bearing a pair of biramous swimming legs. Second to fourth pedigers accounting for 22% of total length in dorsal view. Fifth pedigerous somite as long as genital double somite in dorsal view ( Figure 1C View Figure 1 ). Intercoxal sclerite of legs 1–4 rectangular, naked. Basis with diagonal division articulating it with large, rectangular coxa. Lateral naked hair-like setae on basis of legs 1–4; longer and thicker in third leg than in the other (four times longer in leg 3 than in leg 1) ( Figure 3C View Figure 3 ). Endopodites and exopodites of legs 1–4 triarticulated. Third exopodal segment with spine on distal outer margin relatively short, 0.60–0.66 as long as bearing segment. Outer apical exopodal seta of same segment long, armed with small spinules along outer margin; inner margin with short setules arranged in tight pattern on legs 1–4 ( Figure 3A–C View Figure 3 ). Armature of swimming legs is shown in Table 1.

Fifth legs with one segment, lobes fused medially at base. Each leg represented by single lobe, relatively wide distally, tapering toward base, elongated; lobe armed with three biserially setulated setae, two outer ones subequal in length and width, and inner seta slender, relatively short, about 40% as long as other two setae ( Figures 2E View Figure 2 , 3D View Figure 3 ).

Urosome consisting of fifth pedigerous somite, genital double somite, and one free (anal) somite. Urosome, excluding caudal rami, accounting for 16.7% of total body length. Ratio of lengths of urosomites as (proximal–distal): 40: 40: 20 = 100. Genital double somite with moderately expanded proximal half; posterior half with lateral margins straight ( Figures 1C View Figure 1 , 2E View Figure 2 ). Dorsal surface of genital double somite smooth. Genital double somite bearing relatively short (0.48 mm), basally conjoined ovigerous spines ( Figure 1A View Figure 1 ) inserted ventrally on proximal third of somite. Spines mostly slender along shaft, subequal in length and one of them slightly swollen at distal end ( Figure 3E View Figure 3 ); spines representing about 33% of total body length, barely reaching beyond distal end of caudal setae in the specimens examined. Anal somite relatively long, with moderately divergent lateral margins ( Figure 1C View Figure 1 ). Caudal rami subrectangular, about 1.3 times as long as wide, divergent, each bearing three setae ( Figure 1C View Figure 1 ); middle caudal seta slightly longer than remaining two.

Male. Unknown.

Type locality

Chatham Bay , northern coastline of Isla del Coco (5°33′01.58′′ N, 87°02′18.57′′ W), Costa Rica GoogleMaps .

Etymology

The specific epithet makes reference to the name of the island at which this species was collected, Isla del Coco, Costa Rica.

Remarks

The females of this species were assigned to the genus Cymbasoma on account of their having only three urosomites (fifth pedigerous, genital double, anal somite) and caudal rami each armed with three setae. Most of the known species of Cymbasoma have a fifth leg bearing an inner lobe, developed to different degrees; many of these species belong to two main groups within the genus, one related to C. longispinosus ( Grygier 1994; Suárez-Morales and Escamilla 1997) and the other to C. rigidum (Suárez- Morales 2006). Only a small group of species has a fifth leg with a single lobe armed with three setae, which is the most derived state of this character ( Suárez-Morales et al. 2006); the new species shares this character with C. striatum Isaac, 1975 , C. tumorifrons Isaac, 1975 , C. boxshalli Suárez-Morales, 1993 , C. quintanarooense Suárez-Morales, 1993 (as redescribed by Suárez-Morales and Escamilla 2001), C. bowmani Suárez-Morales and Gasca, 1998 and C. concepcionae Suárez-Morales and Morales-Ramírez, 2003 . Another character shared by this group of species is the relatively long cephalothorax, representing more than 55% of the total body length: C. bowmani (65%) has the longest, those of C. cocoense sp. nov., C. boxshalli , C. quintanaroense and C. concepcionae are 60–61%, and C. tumorifrons (55%) and C. striatum (56%) have relatively shorter cephalothoraxes (see Suárez-Morales 2001a; Suárez-Morales and Gasca 1998; Suárez-Morales and Morales-Ramírez 2003).

The new species differs from these congeners in several characters. In C. cocoense sp. nov., C. boxshalli , C. tumorifrons , C. concepcionae and C. striatum , the inner seta of the fifth leg is shorter and thinner than the other two setae; in C. bowmani and C. quintanaroense the three setae are equally long and thick ( Suárez-Morales and Escamilla 2001; Suárez-Morales and Gasca 1998). The genital double somite differs among these congeners; in the new species and in C. bowmani , the anterior half is slightly expanded, whereas it is strongly swollen or globose in the other species, particularly in C. striatum , C. quintanaroense and C. tumorifrons (see Suárez-Morales 2000, 2002; Suárez-Morales and Escamilla 2001). In C. concepcionae the genital double somite has a characteristic set of rounded protuberances on the lateral margins and the ventral surface of the anterior half; also, it has a field of ventral and lateral protuberances on the fifth pedigerous somite (see Suárez-Morales and Morales-Ramírez 2003).

The new species seems to be most closely related to C. tumorifrons Isaac , a species that was redescribed by Suárez-Morales (2002) from specimens collected in the Mediterranean. The body proportions, including the relative length of the antennules, cephalothorax and genital double somite, are almost identical in the two species. Both also share a protruding anterior margin of the cephalic area between the antennule bases and a general resemblance of the fifth leg; however, they can be distinguished by several subtle characters: the position of the oral papilla, 12.3% of the way back along the cephalothorax in C. tumorifrons compared with 20.5% in the new species. In the new species the cuticular ornamentation between the antennular bases and the oral papilla includes simple cuticular processes (nail-like), whereas in C. tumorifrons these processes are larger and have a more complex structure ( Suárez-Morales 2002). In C. tumorifrons the anterior half of the genital double somite is clearly swollen, almost globose (see Suárez-Morales 2002, fig. 17), whereas it is only weakly expanded in the new species. In lateral view the anteroventral process of the genital somite is moderately developed in the new species compared with strongly developed in C. tumorifrons (see Suárez-Morales 2002, fig. 14). The anal somite is shorter in the new species, about 41% as long as the genital somite compared with 50% in C. tumorifrons . In the new species the ovigerous spines are inserted on the anterior part of the somite, whereas they arise from the middle of the somite in C. tumorifrons ( Suárez-Morales 2002, fig. 17). Further, in C. cocoense sp. nov., the spines are distally asymmetrical with a short, slightly swollen terminal elongation, whereas in C. tumorifrons the spines have an extremely elongate terminal section, without a swelling ( Suárez-Morales 2002, fig. 21). The main differences between these two species are found in the antennule armature; in C. tumorifrons the antennular element 1 (sensu Grygier and Ohtsuka 1995) is a long, spiniform seta reaching the distal third of the second antennular segment (see Suárez-Morales 2002, fig. 22), whereas in C. cocoense this element is distinctly smaller. Also, the setal elements on the second segment are all well developed in C. tumorifrons whereas elements 2d 1–3 are shorter in the new species. On the fourth segment elements 4d 1,2 and 4v 1,2 are stronger in the new species than in C. tumorifrons , and elements of the “b” group are clearly longer in the new species than in C. tumorifrons .

Some degree of morphological variation has been recorded among specimens of some known species of Cymbasoma , including C. bowmani ( Suárez-Morales and Gasca, 1998) and C. davisi ( Suárez-Morales and Pilz 2008) . The present paratype specimens did not show significant variation from the main morphological pattern described for the holotype.