Chasmocarcinus chacei Felder & Rabalais, 1986

(Figs. 3 A, B; 21E; 28F; 35I, J; 49E; 56D; 63K–M; 84C; 89C)

Chasmocarcinus chacei Felder & Rabalais, 1986: 548, figs. 1–3 [type localilty: Gulf of Mexico].— Blow & Bailey 1992: 176 [in list].—Felder et al. 2009: 1081 [in list].—Ng et al. 2008: 76 [in list].— Thoma et al. 2009: 558, 559 [Gulf of Mexico]. Chasmocarcinus cylindricus — Pequegnat 1970: 195.— Pequegnat et al. 1971: 3, pl. 2A [map].— Powers 1977: 12 (part).— Soto 1985: 487, table 1 (part).

Type material. Holotype female (6.6 × 7.5 mm) (USNM 228455), northwestern Gulf of Mexico, East Flower Gardens Banks, NMFS Survey, stn PLB 8, 27°53.97’N, 93°34.79’W, 126 m, 21.10.1982.

Paratypes: 1 female (USNM 228457), northwestern Gulf of Mexico, East Flower Gardens Banks, NMFS Survey, stn PLB 2, 27°53’41”N, 93°34’33”W, 128 m, 21.10.1982; 1 male (4.4 × 5.0 mm) (USNM 228458), 1 male exoskeleton (4.5 × 6.7 mm) (USNM 228456), 27°53.68’N 93°34.54’W, 128 m, 21.10.1982.

Other material examined. Gulf of Mexico. Holotype female (6.6 × 7.5 mm) (USNM 228455), East Flower Gardens Banks, NMFS Survey, stn PLB 8, 27°53.97’N, 93°34.79’W, 126 m, 21.10.1982.—1 male (6.6 × 8.0 mm), 1 female (7.8 × 9.5 mm) (USNM 61489), White Shoals, Dry Tortugas, Florida, W.L. Schmitt coll., 75‒140 m, 27.07.1924.—1 male (USNM 74856), south of Dry Tortugas, Florida, W.L. Schmitt coll., 88 m, 28.07.1932.—1 male (4.8 × 6.7 mm), 1 female (5.4 × 6.0 mm) (ZRC 2013.1417), stn NGMx, 78°07.18’N, 90°56.812’W, 116‒117 m, mud, benthic skimmer, D. Felder & S. Tuederieas coll., 21.04.2011.

Diagnosis. Anterolateral margins of carapace (Fig. 3 C‒E; Felder & Rabalais 1986: fig. 2a, b) smooth, without granular ridges. Orbits (Fig. 21 F; Felder & Rabalais 1986: fig. 2a, b) short, proportionally long eye peduncles. Epistome (Fig. 21 F; Felder & Rabalais 1986: fig. 2c) with semicircular median lobe with median fissure, lateral margins straight. Antennular articles relatively short (Fig. 21 E). Third maxilliped (Fig. 28 F) merus ovate; ischium rectangular, longer than merus. Bulging pterygostomial region, clearly visible from dorsal view. Fingers of major chela of both sexes (Fig. 35 I; Felder & Rabalais 1986: fig. 3b) straight, proportionally short, only slightly longer than propodus in dorsal view; pollex as long as dactylus in large males. Fingers of minor chela of both sexes (Fig. 35 J; Felder & Rabalais 1986: fig. 3c) scissor-like; cutting margin of pollex with low teeth, distal quarter with few small spines. Inner margin of cheliped carpus smooth. Ambulatory legs proportionally short (Fig. 3 A, B: Felder & Rabalais 1986: fig. 3d), folded P5 merus only reaching middle portion of anterolateral margin; subdistal spur present on P5 dactylus (Fig. 63 M). Fused thoracic sternites 1, 2 (Fig. 49 E) broadly triangular, proportionally wide, short. Male pleon (Felder & Rabalais 1986: fig. 2f) with proportionally long, narrow telson. G1 (Fig. 63 K; Felder & Rabalais 1986: fig. 3f, g) stout, straight, distal segment with spinules. G2 (Fig. 63 L; Felder & Rabalais 1986: fig. 3h) about 3/4 G1 length, straight, slender, distal segment long, curved. Female pleon (Fig. 84 C) with lateral margins of somites strongly convex; telson proportionally short. Sterno-pleonal cavity of female (Fig. 89 C) moderately shallow, vulvae close together.

Remarks. Diagnostic for C. chacei is a relatively smooth carapace that lacks granular ridges along the anterolateral margins, and proportionally short orbits and long eye peduncles (Fig. 21 E; Felder & Rabalais 1986: fig. 2a, b), a rectangular third maxilliped ischium that is slightly longer than the merus (Fig. 28 F), and semicircular, proportionally broad and short sternite 1 and 2 (Fig. 49 E).

A molt of a large female from Anguilla (8.3 × 10.1 mm, USNM 228470), outside the normal distribution of C. chacei, and tentatively identified as belonging to this species (Felder & Rabalais 1986: 549) actually represents C. typicus . The fused thoracic sternites 1 and 2 are broadly triangular with parallel sides, proportionally narrow and long, which is diagnostic for C. typicus .

Distribution. Gulf of Mexico. Depth: 86–296 m (Felder et al. 2009).