Chasmocarcinus gemmatus n. sp. (Figs. 3 F; 5C; 21G; 29A; 36A, B; 49G; 56F; 64G‒I) Type material. Holotype male (7.7 × 11.6 mm) (SIO C 1205), Costa Rica, Golfo de Nicoya, Agassiz, 0 9°37.4’N— 0 9°37.7’N, 84°49.0’W— 84°51.8’W, 86 m, 25-feet otter trawl, C. Hubbs coll., 22.04.1973. Diagnosis. Anterolateral margins of carapace (Fig. 3 F) smooth, not cristate. Orbits long, proportionally long eye peduncles (Fig. 21 G). Posterior margin of epistome (Fig. 21 G) with semicircular median lobe with median fissure, lateral margins straight. Antennular articles relatively short (Fig. 21 G). Third maxilliped (Fig. 29 A) ischium elongated, about same size as ovate merus, leaving gap between maxillipeds. Bulging pterygostomial region, clearly visible from dorsal view (Fig. 5 C). Fingers of major chela of male (Fig. 36 A) proportionally long, curved, slightly longer than propodus in dorsal view; pollex as long as dactylus, with short teeth, larger along proximal cutting margin, submarginal parts of cutting edge of dactylus lined with dense short setae. Fingers of minor chela of males (Fig. 36 B) scissor-like; with small, sharp teeth. Outer margin of cheliped carpus (Fig. 3 F) with blunt tooth. Ambulatory legs (Fig. 3 F) proportionally short, folded P5 merus only reaching middle portion of anterolateral margin; no subdistal spur on P5 dactylus. Fused thoracic sternites 1, 2 (Fig. 49 G) broadly triangular, proportionally narrow, long. Male pleon (Figs. 49 G, 56F) with proportionally long, narrow telson. G1 slender, widened subdistal half, spinules along distal third (Fig. 64 G, H). G2 (Fig. 64 I) straight, slender, distal segment long, slightly curved; about 3/4 as long as G1. Female unknown. Etymology. The name is derived from the Latin for “twin,” alluding to the close resemblance of this species to its analogous Western Atlantic species, Chasmocarcinus typicus. Remarks. Chasmocarcinus gemmatus n. sp. is most similar to C. typicus from the Caribbean Sea in the form of the adult major chela, with the fingers long, slender and distinctly curved. Chasmocarcinus gemmatus n. sp. nevertheless differs in having the carapace proportionately broader (Fig. 3 F) (carapace narrower in C. typicus, Fig. 2 A–D); proportionately shorter ambulatory legs (Fig. 3 F) (proportionately shorter in C. typicus, Fig. 2 A–D); the antennular articles are relatively shorter (Fig. 21 G) (usually distinctly longer in C. typicus, Fig. 21 A); and the distal part of the G1 is more sharply tapering and less flared (Fig. 64 G, H) (distal part of G1 distinctly more flared in C. typicus, Fig. 63 A, B). Chasmocarcinus gemmatus n. sp. thus appears to be the Eastern Pacific analog of C. typicus. Chasmocarcinus gemmatus n. sp. can easily be separated from its Eastern Pacific congeners (notably C. latipes, which it has been found together in Golfo de Nicoya, Costa Rica) in having a more trapezoidal carapace, the pterygostomial region being distinct and visible from dorsal view (lower and less swollen in the other species), absence of a spur on P5 (present, for example, in C. chacei), and the dilated median part of the G1 with the tip more flared (evening tapering in the other species with no obvious flare at the tip). Distribution. Pacific coast of Costa Rica. Depth: 86 m.

Published as part of Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), pp. 1-182 in Zootaxa 4209 (1) on pages 20-21, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646