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

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.

Figures

FIGURE 2. Overall dorsal view of species of Chasmocarcinus. A, C. typicus, Trinidad: holotype male 7.8 × 8.7 mm (USNM 6901); B, C. typicus, Trinidad: paratype male 4.1 × 4.7 mm (USNM 6901); C, C. typicus, Brazil: male 4.0 × 5.1 mm (MCZ CRU- 10993, holotype of C. rathbuni); D, C. typicus, Brazil: female 8.6 × 10.5 mm (ZRC 2015.211); E, C. arcuatus, Brazil: male 5.7 × 7.7 mm (ZRC 2015.221); F, C. arcuatus, Brazil: female 4.4 × 6.2 mm (ZRC 2015.222); G, C. arcuatus, Brazil: male 3.7 × 5.1 mm (ZRC 2015.220); H, C. arcuatus, Brazil: ovigerous female 4.6 × 6.1 mm (ZRC 2015.220).

FIGURE 3. Overall dorsal view of species of Chasmocarcinus. A, C. chacei, Gulf of Mexico: male 6.6 × 8.0 mm (USNM 61489); B, C. chacei, Gulf of Mexico: female 7.8 × 9.5 mm (USNM 61489); C, C. cylindricus, Jamaica: male 3.6 × 4.9 mm (USNM 42942); D, C. cylindricus, Puerto Rico: neotype female 4.6 × 6.1 mm (USNM 23765); E, C. cylindricus, Puerto Rico: female 6.9 × 9.2 mm (USNM 24551); F, C. gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205); H, C. hirsutipes, Brazil: holotype male 6.6 × 7.0 mm (after Coelho & Coelho 1998: fig. 5 a).

FIGURE 5. Overall dorsal view of species of Chasmocarcinus, Amboplax n. gen. and Deltopelta n. gen. A, Amboplax peresi, Brazil: male 5.1 × 6.4 mm (ZRC 2015.217); B, Amboplax peresi, Brazil: ovigerous female 4.9 × 6.2 mm (ZRC 2015.217); C, Chasmocarcinus gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205); D, Chasmocarcinus latipes, Ecuador: male 10.5 × 14.5 mm (AMNH 1941 - 10668); E, Deltopelta obliquus, A, Bahamas: holotype male 5.2 × 5.1 mm (USNM 20509); F, Deltopelta obliquus, Belize: female 10.7 × 13.0 mm (PMNH, holotype of Hephthopelta superba); G, Deltopelta obliquus, Belize: female 10.7 × 13.0 mm (PMNH, holotype of Hephthopelta superba, after Boone 1927: fig. 5).

FIGURE 21. Frontal view of cephalothorax of species of Chasmocarcinus. A, C. typicus, Trinidad: holotype male 7.8 × 8.7 mm (USNM 6901); B C. arcuatus, Brazil: male 5.7 × 7.7 mm (ZRC 2015.221); C, D, C. arcuatus, Brazil: male 3.7 × 5.1 mm (ZRC 2015.220); E, C. chacei, Gulf of Mexico: male 6.6 × 8.0 mm (USNM 61489); F, C. cylindricus, Puerto Rico: neotype female 4.6 × 6.1 mm (USNM 23765); G, C. gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205); H, C. hirsutipes, Brazil: holotype female 6.6 × 7.0 mm (after Coelho & Coelho 1998: fig. 5 c).

FIGURE 29. Third maxilliped of species of Chasmocarcinus and Deltopelta n. gen. A, Chasmocarcinus gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205); B, C. hirsutipes, Brazil: holotype male 6.6 × 7.0 mm (after Coelho & Coelho 1998: fig. 6 c); C, Chasmocarcinus latipes, Mexico: holotype female 12.4 × 14.4 mm (USNM 21592); D, Chasmocarcinus latipes, Ecuador: male 10.5 × 14.5 mm (AMNH 1941 - 10668); E, Chasmocarcinus latipes, Mexico: female 9.2 × 13.0 mm (AMNH 16262, holotype female of Chasmocarcinus ferrugineus Glassell, 1936); F, Chasmocarcinus longipes, Colombia: paratype male 5.5 × 6.4 mm (USNM 78785); G, C. meloi, Brazil: holotype male 5.3 × 6.2 mm (after Coelho & Coelho 1998: fig. 8 c); H, Chasmocarcinus mississippiensis, Gulf of Mexico: male 7.2 × 8.8 mm (USNM 101082); I, Deltopelta obliquus, Bahamas: holotype male 5.2 × 5.1 mm (USNM 20509).

FIGURE 36. Chelae of species of Chasmocarcinus. A, B, C. gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205); C, D, C. hirsutipes, Brazil: holotype male 6.6 × 7.0 mm (after Coelho & Coelho 1998: fig. 6 e, f); E, C. latipes, Mexico: holotype female 12.4 × 14.4 mm (USNM 21592); F, C. latipes, Mexico: female 9.2 × 13.0 mm (AMNH 16262, holotype female of Chasmocarcinus ferrugineus Glassell, 1936); G, H, C. latipes, Ecuador: male 10.5 × 14.5 mm (AMNH 1941 - 10668); I, J, C. longipes, Colombia: paratype male 5.5 × 6.4 mm (USNM 78785).

FIGURE 49. Anterior thoracic sternum and male pleon of species of Chasmocarcinus. A, C. typicus, Trinidad: holotype male 7.8 × 8.7 mm (USNM 6901); B, C. typicus, Brazil: male 4.0 × 5.1 mm (MCZ CRU- 10993, holotype of Chasmocarcinus rathbuni); C, C. arcuatus, Brazil: male 5.7 × 7.7 mm (ZRC 2015.221); D, C. arcuatus, Brazil: male 3.7 × 5.1 mm (ZRC 2015.220); E, C. chacei, Gulf of Mexico: male 6.6 × 8.0 mm (USNM 61489); F, C. cylindricus, Jamaica: male 3.6 × 4.9 mm (USNM 42942); G, C. gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205); H, C. hirsutipes, Brazil: holotype male 6.6 × 7.0 mm (after Coelho & Coelho 1998: fig. 7 c).

FIGURE 63. Gonopods and ambulatory dactylus of species of Chasmocarcinus. A ‒ C, C. typicus, Trinidad: holotype male 7.8 × 8.7 mm (USNM 6901); D ‒ F, C. arcuatus, Brazil: male 5.7 × 7.7 mm (ZRC 2015.221); G ‒ J, C. arcuatus, Brazil: male 3.7 × 5.1 mm (ZRC 2015.220); K ‒ M, C. chacei, Gulf of Mexico: paratype male 4.5 × 6.7 mm (USNM 228456, after Felder & Rabalais 1986: fig. 3 e, g, h). A, D, G, ventral view of left G 1; B, E, H, dorsal view of left G 1; I, ventral view of tip of left G 1; K, ventral view of right G 1 (laterally transposed); C, F, J, L, left G 2; M, tip of P 5. Scales: A ‒ H, J ‒ M = 0.5 mm; I = 0.1 mm.

FIGURE 64. Gonopods and epistomes of species of Chasmocarcinus. A ‒ E, C. cylindricus, Jamaica: male 3.6 × 4.9 mm (USNM 42942); F, C. cylindricus, Puerto Rico: female 6.9 × 9.2 mm (USNM 24551); G ‒ I, C. gemmatus n. sp., Costa Rica: male 7.7 × 11.6 mm (SIO C 1205). A, dorsal view of right G 1; B, ventral view of right G 1; C, ventral view of distal part of distal part of right G 1; D, right G 2; E, F, posterior margin of epistome; G, ventral view of left G 1; H, dorsal view of left G 1; I, left G 2. Scales: A, B, D = 0.25 mm; E ‒ I = 0.5 mm; C = 0.05 mm.