Cyrtomaia micronesica, Forges, Bertrand Richer De & Ng, Peter K. L., 2007

Forges, Bertrand Richer De & Ng, Peter K. L., 2007, A new species of Cyrtomaia Miers, 1886 (Crustacea: Decapoda: Brachyura: Majidae) from Micronesia, Zootaxa 1409, pp. 61-67 : 62-67

Cyrtomaia micronesica n. sp.

( Figs. 1–4 , 5B , D)

Cyrtomaia intermedia — Paulay et al., 2003: 497 (not Cyrtomaia intermedia Sakai, 1938 ).

Holotype —male, cl 39.2 mm, cw 42.2 mm, in traps, 270 m, off Haputo, Guam, coll. F. Cushing et al., 9 Oct 1997, ZRC 2006.0163. Paratypes—male, cl 43.9 mm, cw 49.4 mm, dropoff, in traps, 210m, Palau, coll. Coral Reef Research Foundation of Palau, P. Colin & L. B. Colin, 30 Jul 1996, MNHN-B 30233; 1 male, cl 31.2 mm, cw 35.0 mm, 1 female, cl 34.4 mm, cw 37.6 mm, dropoff, in traps, 600 m, Palau, coll. Coral Reef Research Foundation of Palau, P. Colin & L. B. Colin, 30 Jul 1996, ZRC 2006.0164.

Comparative material. Cyrtomaia cornuta Richer de Forges & Guinot, 1988: 1 male, cl 49.6 mm, cw 55.0 mm, station 195, 18°54.8’S 163°22.2’E, 465m, New Caledonia, coll. MUSORSTOM IV, N. O. “Vauban”, 19 Sep 1985, ZRC 2006.0165 (ex MNHN-B 20221); 1 female, ovigerous, cl 49.3 mm, cw 53.0 mm, station CC1, 24°54.96’S 168°21.91’E, 500m, New Caledonia, coll. CHALCAL II, N. O. “Coriolis”, 28 Oct 1986, ZRC 2006.0166 (ex MNHN-B 20222).

Diagnosis. Carapace round with dorsal spines arranged as follows: 1 epigastric spine long, slender, sharp, gently curved, surface smooth; with 2 spines (one on each region) slightly divergent; 1 short mesogastric spine; 2 cardiac tubercles; 1 intestinal tubercule; 1 small hepatic spine; 1 postocular spine strong, sharp; supraorbital border with short, triangular, anteriorly-directed spine; pseudorostral spines longer than rostrum. Dorsal surface of carapace finely granular, with tubercules on branchial regions; ridge joining base of protogastric spine to base of postorbital spine. Basal antennal article with 4 conical spines. Eyes small, with short ocular peduncle reaching level of supraocular spine, with blunt spine on upper part. Chelipeds relatively short in adult male, enlarged distally ( Fig. 4 B, C); surfaces of all articles strongly granular, with row of strong spines on superior border of merus. P2 longer than chelipeds, with spines along superior margins; P3 similar in form but shorter than P2; P3 and P4 smooth with only 1 strong curved spine at distal end of merus. First abdominal segment with a low tubercle. G1 almost straight, with distal part relatively sinuous, tip acute when viewed laterally. G2 very short.

Etymology. The name is derived from the type locality, Micronesia, the group of islands to which Guam and Palau belong.

Remarks. Cyrtomaia micronesica n. sp. is closest in general morphology to C. cornuta Richer de Forges & Guinot, 1988, described from New Caledonia. Cyrtomaia cornuta , however, is a relatively larger species (largest specimen cl 68.0 mm, cw 76.0 mm, cf. Guinot & Richer de Forges, 1988: 44) in contrast to cl 39.2 mm, cw 42.2 mm [holotype male] in C. micronesica ) with the dorsal surface of the carapace clearly less granular as compared to C. micronesica . Cyrtomaia micronesica can also be separated from C. cornuta in that the epigastric spines are more slender, with the surface smooth ( Fig. 2 A) (relatively stronger and more granular spines in C. cornuta ), the propodus of the male cheliped is relatively slender and proportionately smaller (relatively short and prominently enlarged distally in C. cornuta ) ( Fig. 4 B, C), the cardiac region has two blunt tubercles (with two strong spines in C. cornuta ) ( Fig. 2 A), the first abdominal segment has only a low tubercle (a sharp spine in C. cornuta ), the P3 and P5 meri are proportionately longer ( Fig. 1 ) and the spines of the basal antennae article are proportionately much shorter ( Fig. 2 C) than in C. cornuta , and the G1 is relatively more sinuous than the new species, with the distal part more acute (not truncate; Fig. 4 B, D) when viewed laterally.

In C. cornuta , the length of the P2 is similar to that of the cheliped but, the P2 is much longer than the cheliped in C. micronesica ( Fig. 1 ). This character, however, is less evident in the young female specimen of C. micronesica , suggesting that this difference is only useful for adult males.

On the basis of what is known, the two species occur in two different regions. Cyrtomaia micronesica is only known from Guam and Palau; whereas C. cornuta occurs in New Caledonia. It is interesting that all three specimens of C. micronesica were obtained by traps whereas all the New Caledonian material of C. cornuta came from deep-water trawls. The traps from this area in Micronesia have previously yielded several rare and interesting species of homolids, poupinids and majids ( Eldredge, 1980; Williams & Moffitt, 1991). Lucius Eldredge (pers. comm.) notes that these crabs were from deep-water areas with steep gradients, and in a habitat not easy to sample. The holotype of C. micronesica was apparently also obtained from a similarly steeper deep rocky habitat (G. Paulay, pers. comm.). There is accumulating evidence that steep rocky habitats harbour a host of new and supposedly rare species. Unfortunately, these habitats are very difficult to sample, except with tangle nets or traps (see Ng, 2006; Mclay & Ng, 2005). This also suggests that the preferred habitats of C. cornuta and C. micronesica are different, especially since all the material of the former species was obtained by trawls from a flatter ocean bottom.

The Indo-West Pacific genus Cyrtomaia Miers, 1886 , currently contains 28 recognised species (see Guinot & Richer de Forges, 1982a, b, 1986; Richer de Forges & Guinot, 1988, 1990), although Griffin & Tranter (1986) argue that some species should be synonymised as too much emphasis was placed on variable characters.

Figures

FIGURE 1. Cyrtomaia micronesica n. sp. Holotype male, cl 39.2 mm, cw 42.2 mm, ZRC 2006.0163. Overall view.

FIGURE 2. Cyrtomaia micronesica n. sp. Holotype male, cl 39.2 mm, cw 42.2 mm, ZRC 2006.0163. A, dorsal view of carapace; B, dorsal view of pseudorostrum; C, ventral view of rostrum and antennae.

FIGURE 3. Cyrtomaia micronesica n. sp. Holotype male, cl 39.2 mm, cw 42.2 mm, ZRC 2006.0163. A, frontal view of carapace; B, lateral view of carapace; C, lateral view of pseudorostrum and rostrum; D, supraorbital margin and pseudorostrum.

FIGURE 4. Cyrtomaia micronesica n. sp. Holotype male, cl 39.2 mm, cw 42.2 mm, ZRC 2006.0163. A, ventral view of carapace showing thoracic sternum and male abdomen; B, outer view of left chela; C, outer view of right chela.

FIGURE 5. A, C, Cyrtomaia cornuta Richer de Forges & Guinot, 1988, male, cl 49.6 mm, cw 55.0 mm, ZRC 2006.0165; B, D, Cyrtomaia micronesica n. sp., paratype male, cl 43.0 mm, cw 49.4 mm, MNHN-B 30233. A, B, right G 1 s (ventral view); C, D, distal part of right G 1 s (ventral view). Scales: A, B = 1.0 mm; C, D = 0.2 mm.