Mariaplax anfracta ( Rathbun, 1909 ) Rahayu & Ng, 2014

Rahayu, Dwi Listyo & Ng, Peter K. L., 2014, New genera and new species of Hexapodidae (Crustacea, Brachyura) from the Indo-West Pacific and east Atlantic, Raffles Bulletin of Zoology 62, pp. 396-483 : 424-427

Mariaplax anfracta ( Rathbun, 1909) , new combination

( Figs. 22 , 23 )

Lambdophallus anfractus Rathbun, 1909: 113 ; Rathbun, 1910: 348, fig. 36; Guinot, 1979: fig. 33F.

Hexapus anfractus – Manning & Holthuis, 1981: 172, fig. 33; Ng et al., 2008: 86.

Material examined. Paratypes: Thailand: 1 male (5.0 × 3.2 mm), 1 female (6.1 × 4.0 mm), 1 ovigerous female (6.6 × 4.3 mm) ( USNM 39752 ), west coast of Koh Chang, Gulf of Thailand, 6 fms, 26 January 1900 . Others: Thailand: 1 female (5.2 × 3.4 mm) ( ZRC 2012.1019 ), sand flat, Ko Sirae , Phuket, coll. T. Komai, 22 December 2009 . Malaysia: 1 ovigerous female (4.1 × 2.8 mm) ( ZRC 1965.11.24.6), Penang Strait .

Diagnosis. Carapace subquadrate about 1.5 times as broad as long, dorsal surface finely granulated, punctate with short pubescence; regions indistinct. Anterolateral margin arcuate, gently granular; posterolateral margin with protuberance, posterolateral corner with angled prominence over base of posterior pereopods. Orbit distinct, transverse; eye almost immovable. Pterygostomial region covered by granules and with row of 4 striae. Third maxillipeds broad, completely covering buccal cavity; ischium almost as long as broad, slightly longer than merus, with scattered granules, mesial margin straight; exopod narrow. Chelipeds asymmetrical, major chela slightly gaping when fingers closed; large teeth on cutting edge of dactylus and fixed finger; minor chela with relatively wider gap when fingers closed. P2–P4 tomentose, surfaces granulated, P3 stoutest, longest; merus of P4 2.5 times as long as broad, with distinct median groove on lateral surface. Male thoracic sternum relatively broad, surface finely granular; deep, wide transverse groove extends obliquely from edge of sternoabdominal cavity, subparallel to frontal margin, not reaching base of chelipeds. Sternoabdominal cavity reaching distal margin of thoracic sternite 4. Male abdomen relatively narrow, surface granular, somites 1 and 2 free; somites 3–5 fused, lateral margin slightly arched; somite 6 as long as wide, lateral margin expanded into blunt triangular projection subproximally; telson subtriangular, distal margin rounded, sparsely setose. G1 S-shaped, distal part tapered, sparse short setae present medially; distal part exposed on thoracic sternal groove, not concealed under abdomen. Female abdomen relatively broad, with 6 somites free and telson.

Description. Carapace subquadrate about 1.5 times as broad as long, dorsal surface finely granulated, punctate with short pubescence; regions indistinct, with shallow median H-shaped depression ( Fig. 22A, C ). Anterolateral margin arcuate, gently granular; posterolateral margin with protuberance, posterolateral corner with angled prominence over base of posterior pereopods ( Figs. 22A, C , 23A ). Front deflexed, divided into 2 lobes, not projecting beyond edge of orbits ( Fig. 22B ). Orbit distinct, transverse; eye almost immovable, small, cornea pigmented, wider than peduncle. Pterygostomial region covered by granules and with row of oblique striae. Third maxillipeds broad ( Fig. 23D ), completely covering buccal cavity; ischium almost as long as broad, slightly longer than merus, with scattered granules, mesial margin straight, narrow proximal part very short, about one-tenth length of ischium, dactylus, propodus and carpus cylindrical, dactylus longer than propodus, combined length of dactylus, propodus and carpus slightly longer than that of merus and ischium; exopod narrow, about 0.4 times width of ischium slightly granular, flagellum well developed.

Chelipeds asymmetrical ( Fig. 22B ). Major chela ( Fig. 23E ) slightly gaping when fingers closed; large teeth present on cutting edge of dactylus and fixed finger; outer surface of dactylus with shallow, narrow groove medially, small granules and sparse setae present proximally; inner surface near upper margin with longitudinal ridge; palm almost as long as wide or slightly longer than wide, surface finely tuberculate; carpus glabrous dorsally, inner angle blunt, unarmed; merus short, unarmed, fringe of setae dorsomesially. Minor chela with relatively wider gap when fingers closed; cutting edge of dactylus and fixed finger with row of moderately large teeth; dactylus with tubercles on upper half of outer surface; inner surface with longitudinal ridge near upper margin; outer surface of fixed finger with longitudinal ridge; dorsal surface of palm covered by granules, carpus and merus unarmed, fringe of sparse setae on each dorsomesial margin.

P2–P4 tomentose, surfaces granular ( Fig. 22A, C ). P2 most slender; dactylus gently upcurved, fringe of long setae on upper and lower margins, slightly shorter than propodus; propodus with row of tiny tubercles on upper and lower margins with long setae; carpus longer than propodus, unarmed, tufts of setae distally; merus twice length of carpus, upper and lower outer surface with rows of granules accompanied by tufts of long setae, shallow longitudinal groove on outer surface medially. P3 stouter and longer than P2; dactylus straight, longer than propodus; propodus and carpus with long setae on upper and lower margins, and most of upper outer surface; merus slightly more than twice length of carpus, upper and lower outer surfaces with rows of granules accompanied by tufts of long setae, shallow longitudinal groove on outer surface medially. P4 stouter and shorter than P3, dactylus gently upcurved; upper and lower outer surface of propodus and carpus with rows of granules obscured by tufts of long and short setae; merus slightly twice length of carpus, 2.5 times as long as broad, upper and lower outer surfaces with rows of granules obscured by tufts of long and short setae, shallow longitudinal groove on outer surface medially.

Male thoracic sternum relatively broad ( Fig. 23B, C ), surface finely granular; sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated from sternite 4 by distinct ridge; deep, wide transverse groove extends obliquely from edge of sternoabdominal cavity ( Fig. 23B ), thoracic sternal groove subparallel to frontal margin, not reaching base of chelipeds; sternite 8 exposed, rectangular, equal to length of male abdominal somite 1; sternoabdominal cavity reaching distal margin of thoracic sternite 4 ( Fig. 23B ). Male abdomen relatively narrow ( Fig. 23C ), surface granular, somites 1 and 2 free; somites 3–5 fused, lateral margin slightly arched; somite 6 as long as wide, lateral margin expanded into blunt triangular projection subproximally; telson subtriangular, distal margin rounded, sparsely setose ( Fig. 23C ).

G1 ( Fig. 23F, G ) S-shaped, distal part tapered, sparse short setae present medially; distal part exposed on thoracic sternal groove, not concealed under abdomen.

Female abdomen relatively broad, with 6 free somites and subtriangular telson ( Fig. 23H ).

Colour. Not known.

Remarks. Mariaplax anfracta , new combination, is a small sized species. One paratype female and a non-type female from Penang, both ovigerous, measured less than 7 mm in carapace width.

Records of “ Hexapus anfractus ” from China by Huang (1994: 592) and Yang et al. (2008: 772) cannot be reliably identified and are probably mixed. Specimens from China we have examined that have been identified as this species belong to two new species, Mariaplax chenae and M. sinensis .

Type locality. West coast of Koh Chang, Gulf of Thailand .

Distribution. Gulf of Thailand, Phuket; and Penang Strait, Malaysia. Intertidal to 12 m.

Figures

Fig. 22. Mariaplax anfracta (Rathbun, 1909). A, B, paratype female (6.1 × 4.0 mm) (USNM 39752); C, paratype male (5.0 × 3.2 mm) (USNM 39752). A, C, overall views of carapace, chelipeds and P2–P4; B, frontal view of cephalothorax.

Fig. 23. Mariaplax anfracta (Rathbun, 1909). A–G, paratype male (5.0 × 3.2 mm) (USNM 39752); H, female (4.1 × 2.8 mm) (ZRC 1965.11.24.6). A, dorso-lateral margin of carapace; B, thoracic sternites 1–4, showing sternoabdominal cavity and thoracic sternal groove; C, thoracic sternites3 and 4, showing thoracic sternal groove and telson; D, right third maxilliped; E, major chela; F, G, G1; H, female abdomen and telson. Scale bars = 1.0 mm.