Chasmocarcinus gemmatus , Ng, Peter K. L. & Castro, Peter, 2016

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182: 20-21

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Chasmocarcinus gemmatus

n. sp.

Chasmocarcinus gemmatus  n. sp.

( Figs. 3View FIGURE 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., 22.04.1973GoogleMaps  .

Diagnosis. Anterolateral margins of carapace ( Fig. 3View FIGURE 3 F) smooth, not cristate. Orbits long, proportionally long eye peduncles ( Fig. 21View FIGURE 21 G). Posterior margin of epistome ( Fig. 21View FIGURE 21 G) with semicircular median lobe with median fissure, lateral margins straight. Antennular articles relatively short ( Fig. 21View FIGURE 21 G). Third maxilliped ( Fig. 29View FIGURE 29 A) ischium elongated, about same size as ovate merus, leaving gap between maxillipeds. Bulging pterygostomial region, clearly visible from dorsal view ( Fig. 5View FIGURE 5 C). Fingers of major chela of male ( Fig. 36View FIGURE 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. 36View FIGURE 36 B) scissor-like; with small, sharp teeth. Outer margin of cheliped carpus ( Fig. 3View FIGURE 3 F) with blunt tooth. Ambulatory legs ( Fig. 3View FIGURE 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. 49View FIGURE 49 G) broadly triangular, proportionally narrow, long. Male pleon ( Figs. 49View FIGURE 49 G, 56F) with proportionally long, narrow telson. G1 slender, widened subdistal half, spinules along distal third ( Fig. 64View FIGURE 64 G, H). G2 ( Fig. 64View FIGURE 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. 3View FIGURE 3 F) (carapace narrower in C. typicus  , Fig. 2View FIGURE 2 A –D); proportionately shorter ambulatory legs ( Fig. 3View FIGURE 3 F) (proportionately shorter in C. typicus  , Fig. 2View FIGURE 2 A –D); the antennular articles are relatively shorter ( Fig. 21View FIGURE 21 G) (usually distinctly longer in C. typicus  , Fig. 21View FIGURE 21 A); and the distal part of the G1 is more sharply tapering and less flared ( Fig. 64View FIGURE 64 G, H) (distal part of G1 distinctly more flared in C. typicus  , Fig. 63View FIGURE 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.


Scripps Institution of Oceanography