Mariaplax propinqua, 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 : 449

Mariaplax propinqua , new species

( Figs. 43–45 )

Material examined. Holotype: male (10.3 × 6.5 mm) ( IOCAS), station 6197, 21°00'N 109°00'E, Tonkin Gulf, China . Paratype: China: 1 male (9.0 × 5.6 mm) ( ZRC 2012.1033 ), station 6214, 20°45'N 108°30'E, coll. cruise boat 228, 15 February 1960 .

Diagnosis. Carapace subquadrate, about 1.5 times as broad as long, dorsal surface granulated; regions indistinct, with shallow median H-shaped depression ( Fig. 43A ). Anterolateral margin arcuate; posterolateral margin with angled prominence over base of posterior pereopods ( Figs. 43A , 45A ). Front deflexed, divided into 2 lobes, not projecting beyond edge of orbits ( Fig. 43B ). Eye slightly movable, small, cornea pigmented, wider than peduncle. Pterygostomial region with row of oblique striae ( Figs. 43B, C , 45B ). Third maxillipeds broad ( Figs. 43C , 44A , 45E ), completely covering buccal cavity; ischium slightly longer than merus, combined length of dactylus, propodus and carpus slightly shorter than that of merus and ischium; exopod narrow, 0.3 width of ischium, slightly granular, flagellum well developed. Chelipeds asymmetrical ( Fig. 44B, C ). Fingers gaping when closed, palm of both chela finely tuberculate ( Figs. 44B, C , 45G, H ). P2–P4 tomentose, surfaces granulated ( Fig. 43A ); merus of P4 3.5 times as long as broad, shallow longitudinal groove on outer surface medially; dactylus of P4 gently upcurved. Male thoracic sternum relatively broad ( Figs. 44A , 45C, D ), surface finely granular; sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated from sternite 4 by distinct ridge; transverse sternal groove extends obliquely from edge of sternoabdominal cavity, almost reaching base of chelipeds ( Figs. 44A , 45C, D ); sternite 8 exposed, triangular, slightly shorter than abdominal somite 1; sternoabdominal cavity reaching middle to thoracic sternite 4 ( Figs. 44A , 45C ). Male abdomen relatively narrow ( Figs. 44A , 45F ), 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 subpentagonal, distal margin rounded, sparsely setose. G1 ( Fig. 45I, J ) S-shaped, distal part tapered, sparse short setae present medially; row of 3 large teeth on lateral margin medially; distal part exposed on thoracic sternal groove, not concealed under abdomen. Female unknown.

Colour. Not known.

Etymology. From the Latin propinqua for close; alluding to the similarity of the new species with M. anfracta .

Remarks. This species closely resembles M. anfracta in the shape of G1 and the tuberculation of carapace, chelipeds and P2 to P4. However, the G1 of M. propinqua , new species, is relatively more slender with a row of three strong teeth on the lateral margin medially ( Fig. 45I, J ) (G1 is relatively stouter, without the presence of teeth in M. anfracta ( Fig. 23F, G ). In addition, the carapace and anterior thoracic sternum are also relatively wider in M. propinqua ( Figs. 43A , 44A versus Figs. 22A , 23B, C ). The telson of M. anfracta is subtriangular while in M. propinqua is subpentagonal, furthermore P2–P4 are shorter in M. anfracta , the merus of P4 is 2.5 as long as wide ( Figs. 22A, C ) versus 3.5 as long as wide in M. propinqua ( Fig. 43A ).

Type locality. Tonkin Gulf, Vietnam.

Distribution. Tonkin Gulf, Vietnam. Subtidal.

Figures

Fig. 43. Mariaplax propinqua, new species, holotype male (10.3 × 6.5 mm) (IOCAS). A, overall view of carapace, chelipeds and P2–P4; B, frontal view of cephalothorax; C, ventral view of cephalothorax.

Fig. 44. Mariaplax propinqua, new species, holotype male (10.3 × 6.5 mm) (IOCAS).A, abdomen and telson; B, major chela; C, minor chela.

Fig. 45. Mariaplax propinqua, new species, holotype male (10.3 × 6.5 mm) (IOCAS). A, dorsolateral margin of carapace; B, anterior view of cephalothorax; C, thoracic sternites 3–5, showing thoracic sternal groove and telson; D, thoracic sternites 1–5, showing sternoabdominal cavity and thoracic sternal groove; E, left third maxilliped; F, male abdomen and telson, G, major chela; H, minor chela; I, J, G1. Scale bars = 1.0 mm.

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.

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.