Mariaplax galaxeae, 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 : 435-438

Mariaplax galaxeae , new species

( Figs. 1G , 32 , 33 )

Material examined. Holotype: female (4.2 × 3.2 mm) ( ZRC 2013.1690 ), station TB99, Singapore Strait , 1°18'861N 104°05'128, 33.7–36.7 m, Singapore, coll. RV Galaxea , 28 May 2013.

Diagnosis. Carapace subquadrate, about 1.4 times as broad as long; dorsal surface covered by tubercles; regions indistinct ( Figs. 32A ). Anterolateral margin arcuate; posterolateral corner with slight protuberance angle over base of posterior pereopods. Eye small, slightly movable, cornea globular ( Fig. 32C ). Pterygostomial region with row of long and short striae with scattered tubercles. Third maxillipeds relatively broad, almost completely covering buccal cavity ( Figs. 32C , 33B ); ischium of third maxillipeds longer than merus, with straight margin; combined length of dactylus, propodus and carpus slightly shorter than that of merus and ischium; exopod narrow, 0.3 times width of ischium, flagellum well developed. Chelipeds stout, unequal, covered by tubercles ( Fig. 32B, C ); major chela with gap when fingers closed, large teeth on cutting edges; dactylus with shallow groove on outer surface, palm slightly wider than long; minor chela with narrow gap between closed fingers, smaller teeth on cutting edges; dactylus with shallow longitudinal groove medially. P2–P4 relatively long ( Fig. 32A ), long setae on anterior and posterior margin of dactylus, propodus, short setae on carpus and merus; merus of P4 about 2.6 times as long as broad, longitudinal groove on outer face; dactylus of P2 and P4 slightly upcurved, dactylus of P3 straight. Female thoracic sternum broad ( Fig. 32B ), covered by tubercles; sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 and 4 fused, abdominal cavity reached distal margin of sternite 3. Female abdomen relatively broad ( Figs. 32B , 33C ); all somites and telson free; somite 6 slightly longer than telson; telson with rounded tip, margin with sparse setae. Male unknown.

Colour. Carapace cream, mottled light and dark brown; chelipeds and P2−P4 light brown ( Fig. 1G ).

Etymology. Named after the Tropical Marine Science Institute research vessel “ Galaxea ”, which was used during Singapore Strait Expedition of the Comprehensive Marine Biodiversity Survey for collecting material.

Remarks. Mariaplax galaxeae , new species, resembles M. cyrtophallus , new species, and M. mica , new species, in having the carapace, chelipeds and P2–P4 strongly tuberculated. Differences can be seen in the shape of the third maxillipeds and the propotion of width to length of the carapace. In M. galaxeae , the mesial and lateral margins along the distal three quarterof the ischium of the third maxilliped are parallel, straight, the narrow proximal part relatively short ( Fig. 33B ), while in M. cyrtophallus and M. mica , the mesial margin is oblique with slightly expanded subproximally, the narrow proximal part short ( Fig. 29E and Fig. 38B , respectively). The carapace of M. galaxeae is visibly more quadrangular with 1.4 times as broad as long compared to 1.5 as broad as long in M. cyrtophallus and M. mica . Furthermore, the pereopods are shorter in M. galaxeae , which has the merus of P4 2.6 as long as broad whereas in M. cyrtophallus and M. mica it is 3.4 and 3.6 times s long as broad respectively.

The shape of the third maxilliped is comparable to that of M. anfracta , but the narrow proximal part of the ischium is even shorter in M. anfracta ( Fig. 33B versus Fig. 23D ). The abdomen of the same size female is also relatively broader in M. anfracta ( Fig. 23H ) compare to M. galaxeae ( Fig. 33C ).

Type locality. Singapore Strait, Singapore.

Distribution. Singapore Strait, Singapore. Subtidal, 33– 36 m.

Figures

Fig. 1. Colours in life. A, Hexapinus simplex, new species, paratype male (8.7 × 5.0 mm) (MZB), Lombok, Indonesia; B, Hexapinus simplex, new species, male (9.3 × 5.8 mm) (ZRC), Lembeh Straits, Sulawesi Indonesia; C, Hexapinus simplex, new species, male (12.6 × 8.4 mm) (RUMF-ZC-2110), Tekebu, Amami-Ohshima Island, Japan; D, Hexapinus simplex, new species, male (12.6 × 8.4 mm) (ZRC 2013.1688), Funaura, Iriomote Island, Japan; E, Hexapinus simplex, new species, female (8.3 × 6.0 mm) (ZRC 2013.1687), Raffles Reserve near Raffles Lighthouse, Singapore; F, Hexapinus simplex, new species, male (11.2 × 7.0 mm) (ZRC), Pulau Senang, Singapore; G, Mariaplax galaxeae, new species, holotype female (4.2 × 3.2 mm) (ZRC 2013.1690), Singapore Strait; H, Mariaplax chenae, new species, East China Sea (courtsey W.-L. Liu, specimen not examined); I, Mariaplax secus, new species, holotype male (4.7 × 3.0 mm) (MNHN IU-2013-916), Madang, Papua New Guinea; J, Mariaplax mica, new species, holotype female (6.7 × 4.5 mm) (NMCR 39069), Bohol Sea, Philippines.

Fig. 32. Mariaplax galaxeae, new species, holotype female (4.2 × 3.2 mm) (ZRC 2013.1690). A, overall view of carapace, chelipeds and P2–P4; B, ventral view of cephalothorax; C, frontal view of cephalothorax.

Fig. 33. Mariaplax galaxeae, new species, holotype female (4.2 × 3.2 mm) (ZRC 2013.1690). A, dorsal view of carapace; B, left third maxilliped; C, abdomen and telson. Scale bars: A, C = 1.0 mm; B = 0.5 mm.

Fig. 29. Mariaplax cyrtophallus, new species, holotype male (6.5 × 3.8 mm) (MZB). A, dorso-lateral margin of carapace; B, thoracic sternites 1–5, showing sternoabdominal cavity and thoracic sternal groove; C, thoracic sternites 1–5, showing thoracic sternal groove and telson; D, anterior view of cephalothorax; E, left third maxilliped; F, male abdomen and telson, G, major chela; H, minor chela; I, left P4; J, K, left G1. Tubercles on thoracic sternum omitted. Scale bars = 1.0 mm.

Fig. 38. Mariaplax mica, new species, holotype female (6.7 × 4.5 mm) (NMCR 39069). A, dorsolateral margin of carapace; B, left third maxilliped; C, abdomen and telson. 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.