Chasmocarcinus mississippiensis Rathbun, 1931

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 26-27

Chasmocarcinus mississippiensis Rathbun, 1931

( Figs. 4 H; 22E; 29H; 37C, D; 50F; 57C; 66A‒C; 85B; 89H)

Chasmocarcinus mississippiensis Rathbun, 1931: 72 [type localilty: Gulf of Mexico].— Dawson 1966: 177, table 1 [Gulf of Mexico].— Franks et al. 1972: 64 [Gulf of Mexico].— Felder 1973: 70, pl. 10, fig. 2 [in list].— Powers 1977: 112.— Felder & Rabalais 1986: 554, figs. 5, 6 [Gulf of Mexico].— Blow & Bailey 1992: 176 [in list].—Coelho & Coelho 1998: 813 [in list].—Felder et al. 2009: 1081 [in list].— Thoma et al. 2009: 558, 559 [Gulf of Mexico].

Chasmocarcinus mississipiensis [sic]— Serène 1964a: 258 [in list].—Ng et al. 2008: 76 [in list].

Type material. Holotype male (8.3 × 10.4 mm) ( USNM 64074 ); Mississippi, Mississippi Sound near Horn I., 3.7– 9 m, 0 5.04.1931.

Other material examined. Gulf of Mexico. 7 males , 2 males (5.2 × 6.6 mm, 7.2 × 8.8 mm), 3 females (USNM 101082), Sabine Pass, Texas, W.G. Hewat coll., 06.1957.—1 male (8.2 × 11.0 mm), 1 female (9.2 × 12.5 mm) ( USNM 72846 ), Mississippi Sound near Horn I. , Mississippi, Allen & Daily coll., 04.1931.—1 female (9.6 × 12.4 mm) (USNM 150090), Mississippi Sound off west end of Horn I. , Mississippi, Hermes , 20‒30 ft., 20.04.1973.— 3 males , 3 females ( USNM 102364 ), 2 miles NW Fort Massachusetts, Ship I. , Mississippi, D. Moore coll., 03.07.1956.—1 ovigerous female (7.3 × 9.6 mm) (USNM 102363), Dog Keys Pass off Horn I., 6–7.7 m, D. Moore coll., 20.06.1957.—1 male (5.7 × 6.8 mm) (USNM 104735), near Rockport, Texas, T. Hefferman coll., no date— 1 male (6.8 × 5.7 mm) ( ZRC 2013.1419 ), northwestern Gulf of Mexico, oil platform survey, stn Post BECO, 1986. — 1 female (8.2 × 6.1 mm) ( ZRC 2013.1420 ), northwestern Gulf of Mexico, oil platform survey, stn Post BEAV, 1986.

Diagnosis. Carapace ( Fig. 4 H; Felder & Rabalais 1986: fig. 5a–c) with raised, granular ridge along anterolateral margins. Epistome ( Fig. 22 E) with semicircular median lobe with median fissure, lateral margins straight ( Felder & Rabalais 1986: fig. 5c). Orbits ( Fig. 22 E) long, proportionally long eye peduncles. Antennular articles relatively short ( Fig. 22 E). Third maxilliped ( Fig. 29 H) merus broadly ovate; ischium quadrate, as long as merus. Bulging pterygostomial region, clearly visible from dorsal view. Ambulatory legs ( Fig. 4 H) proportionally short, stocky, folded P5 merus only reaching middle portion of anterolateral margin; subdistal spur present on P5 dactylus ( Fig. 66 C). Fingers of major chela ( Fig. 37 C, D; Felder & Rabalais 1986: fig. 6d, e) of large males proportionally short, only slightly longer than propodus in dorsal view; pollex as long as dactylus in large males. Fingers of minor chela ( Fig. 37 D; Felder & Rabalais 1986: fig. 6c) scissor-like; with small, sharp teeth. Anterior margin of ventral surface of propodus, proximal portion of pollex of major chela of large males smooth, without tufts of long setae. Inner margin of cheliped carpus smooth but tooth sometimes present ( Felder & Rabalais 1986). Fused thoracic sternites 1, 2 ( Fig. 50 F) broadly triangular, proportionally wide, short. Male pleon ( Figs. 50 F, 57C) with proportionally long, narrow telson. G1 ( Fig. 66 A) stout, distal part thickened in large individuals, distal segment straight with spinules. G2 ( Fig. 66 B; Felder & Rabalais 1986: fig. 6h) about 4/5 G1 length, straight, slender, distal segment long, curved. Female pleon ( Fig. 85 B) with lateral margins of somites strongly convex; telson proportionally short. Sterno-pleonal cavity of female ( Fig. 89 H) moderately shallow, vulvae close together.

Remarks. Diagnostic to C. mississippiensis is a conspicuous raised, granular ridge along the anterolateral margins of the carapace ( Figs. 4 H, 22E; Felder & Rabalais 1986: fig. 5a, c) and the maxilliped 3 merus is broadly ovate and the ischium quadrate ( Fig. 29 H). The distal part of the G1 is characteristically thickened in large individuals. The subdistal spur on the P5 dactylus lies flat against the distal part of the dactylus.

Felder & Rabalais (1986: 560) listed several characters that are useful in distinguishing C. mississippiensis from C. chacei , both of which are often found sympatrically in the Gulf of Mexico. They also pointed out that the characteristic granular anterolateral ridge and a “granulate tooth or lobe” on the inner angle of the cheliped carpus of C. mississippiensis are also found in the two eastern Pacific species, C. latipes and C. longipes , which is also present in the third eastern Pacific species, C. gemmatus n. sp.

Distribution. Gulf of Mexico. Depth: less than 10–100 m (Felder et al. 2009).

Figures

FIGURE 4. Overall dorsal view of species of Chasmocarcinus. A, C. latipes, Mexico: holotype female 12.4 × 14.4 mm (USNM 21592); B, C. latipes, Ecuador: male 10.5 × 14.5 mm (AMNH 1941 - 10668); C, C. latipes, Ecuador: male 10.5 × 14.3 mm (AMNH 1941 - 10668); D, C. latipes, Mexico: female 9.2 × 13.0 mm (AMNH 16262, holotype female of Chasmocarcinus ferrugineus Glassell, 1936); E, C. latipes, Mexico: female 7.5 × 10.5 mm (AMNH 16262, paratype female of Chasmocarcinus ferrugineus Glassell, 1936); F, C. 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 a); H, C. mississippiensis, Gulf of Mexico: holotype male 8.3 × 10.4 mm (USNM 64074).

FIGURE 22. Frontal view of cephalothorax of species of Chasmocarcinus, Amboplax n. gen. and Deltopelta n. gen. A, Chasmocarcinus latipes, Mexico: holotype female 12.4 × 14.4 mm (USNM 21592); B, Chasmocarcinus latipes, Mexico: female 9.2 × 13.0 mm (AMNH 16262, holotype female of Chasmocarcinus ferrugineus Glassell, 1936); C, Chasmocarcinus longipes, Colombia: paratype male 5.5 × 6.4 mm (USNM 78785); D, Chasmocarcinus meloi, Brazil: holotype female 5.3 × 6.2 mm (after Coelho & Coelho 1998: fig. 8 b); E, Chasmocarcinus mississippiensis, Gulf of Mexico: holotype male 8.3 × 10.4 mm (USNM 64074); F, G, Amboplax peresi, Brazil: male 5.1 × 6.4 mm (ZRC 2015. 217); H, Deltopelta obliquus, Bahamas: holotype male 5.2 × 5.1 mm (USNM 20509).

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 37. Chelae of species of Chasmocarcinus, Amboplax n. gen. and Deltopelta n. gen. A, B, Chasmocarcinus meloi, Brazil: holotype male 5.3 × 6.2 mm (after Coelho & Coelho 1998: fig. 9 a, b); C, D, Chasmocarcinus mississippiensis, Gulf of Mexico: holotype male 8.3 × 10.4 mm (USNM 64074); E, F, Amboplax peresi, Brazil: male 5.1 × 6.4 mm (ZRC 2015.217); G, Deltopelta obliquus, Bahamas: holotype male 5.2 × 5.1 mm (USNM 20509).

FIGURE 50. Anterior thoracic sternum and male pleon of species of Chasmocarcinus, Amboplax n. gen. and Deltopelta n. gen. A, C, Chasmocarcinus latipes, Ecuador: male 10.5 × 14.5 mm (AMNH 1941 - 10668); B, Chasmocarcinus longipes, Colombia: paratype male 5.5 × 6.4 mm (USNM 78785); D, Chasmocarcinus latipes, D, Mexico: male 8.3 × 11.0 mm (SIO C 319); E, Chasmocarcinus meloi, Brazil: holotype male 5.3 × 6.2 mm (after Coelho & Coelho 1998: fig. 9 d); F, Chasmocarcinus mississippiensis, Gulf of Mexico: male 7.2 × 8.8 mm (USNM 101082); G, Amboplax peresi, Brazil: male 5.1 × 6.4 mm (ZRC 2015. 217); H, Deltopelta obliquus, Bahamas: holotype male 5.2 × 5.1 mm (USNM 20509).

FIGURE 66. Gonopods and right P 5 dactylus of species of Chasmocarcinus and Amboplax n. gen. A ‒ C, Chasmocarcinus mississippiensis, Gulf of Mexico: male, carapace width 7.9 mm (USNM 228466, after Felder & Rabalais 1986: fig. 6 g, h, i); D ‒ F, Amboplax peresi, Brazil: male 5.1 × 6.4 mm (ZRC 2015.217). A, ventral view of right G 1 (laterally transposed); B, right G 2; C, tip of right P 5; D, ventral view of left G 1; E, dorsal view of left G 1; F, left G 2. Scales = 0.5 mm.

FIGURE 85. Female thoracic sternum and pleon of species of Chasmocarcinus, Amboplax n. gen. and Deltopelta n. gen. A, Chasmocarcinus longipes, Colombia: paratype female 5.6 × 6.8 mm (USNM 78785); B, Chasmocarcinus mississippiensis, Gulf of Mexico: female 9.6 × 12.4 mm (USNM 150090); C, Amboplax peresi, Brazil: ovigerous female 4.9 × 6.2 mm (ZRC 2015.222); D, Deltopelta obliquus, Belize: female 10.7 × 13.0 mm (PMNH, holotype of Hephthopelta superba).

FIGURE 89. Vulvae of species of Chasmocarcinus, Amboplax n. gen. and Deltopelta n. gen. A, Chasmocarcinus typicus, Trinidad: paratype female 6.5 × 6.8 mm (USNM 6901); B, Chasmocarcinus arcuatus, Brazil: female 4.4 × 6.2 mm (ZRC 2015.222); C, Chasmocarcinus chacei, Gulf of Mexico: female 7.8 × 9.5 mm (USNM 61489); D, Chasmocarcinus cylindricus, Puerto Rico: female 6.9 × 9.2 mm (USNM 24551); E, Chasmocarcinus 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, Chasmocarcinus longipes, Colombia: paratype female 5.6 × 6.8 mm (USNM 78785); H, Chasmocarcinus mississippiensis, Gulf of Mexico: female 9.6 × 12.4 mm (USNM 150090); I, Amboplax peresi, Brazil: ovigerous female 4.9 × 6.2 mm (ZRC 2015. 217); J, Deltopelta obliquus, Belize: female 10.7 × 13.0 mm (PMNH, holotype of Hephthopelta superba).