Mariaplax sundaica, Rahayu & Widyastuti, 2018

Rahayu, Dwi Listyo & Widyastuti, Ernawati, 2018, Additions to the Indonesian crab fauna of the genus Mariaplax Rahayu & Ng, 2014, and notes on Hexapus timika Rahayu & Ng, 2014 (Crustacea, Decapoda, Brachyura, Hexapodidae), Zootaxa 4379 (2), pp. 231-246 : 241-244

Mariaplax sundaica n. sp.

( Figs. 9 , 10 )

Material examined. Holotype, female (5.3 × 3.1 mm) ( MZB Cru 4683), Selat Sunda, Indonesia, 16 February 2002.

Diagnosis. Carapace subquadrate, about 1.7 times as broad as long, dorsal surface strongly granulated; regions indistinct, with shallow depression on branchial region ( Figs. 9A, B , 10A ). Eye small, slightly movable, cornea black, wider than granular stalk ( Fig. 9B, F ). Pterygostomial region ( Fig. 9D ) covered by granules, with row of 4 oblique striae.

Third maxillipeds broad ( Figs. 9D, E , 10B ); ischium slightly longer than merus, slightly expanded subproximally, with slightly oblique mesial margin, combined length of dactylus, propodus and carpus almost as long as merus and ischium; exopod relatively narrow, about 0.4 width of ischium, flagellum well developed.

Chelipeds asymmetrical, covered by closely spaced tubercles ( Fig. 9A ). Major chela ( Figs. 9G , 10D ) with slightly gaping finger when closed; dactylus with longitudinal ridge at midline not reaching proximal part, tubercles on proximal third; palm as long as broad; outer surface of palm and carpus covered with closely-spaced tubercles; merus short, covered with tubercles, fringe of setae dorsomesially. Minor chela ( Figs. 9H , 10E ) with relatively narrower gap when fingers closed; dactylus with longitudinal ridge at midline not reaching proximal part, cutting edges of dactylus and fixed finger with row of small teeth outer surface of palm carpus and merus covered by closely-spaced tubercles; fringe of setae on each upper inner margin of merus.

P2–P4 ( Fig. 9A ) relatively long, slender; dactylus gently upcurved; P3 longest; dactylus of P2, P3 shorter than propodi and carpi; meri with distinct median groove on lateral face, 3.6 and 3.5 as long as broad, respectively ( Fig. 10F, G ); dactylus of P4 longer than propodus and carpus, merus of P4 relatively stout, about 3.3 times longer than broad, lateral face covered by dense tubercles, without discernible median groove ( Fig. 10H ).

Female thoracic sternum broad ( Fig. 9C, D ), surface prominently granular; sternites 1 and 2 fused, separated from sternite 3 by distinct furrow; sternite 3 separated from sternite 4; sternites 4–7 well developed, separated from each other by distinct suture; sternite 8 not exposed; sternopleonal cavity reaches base of sternite3 ( Fig. 9D, E ). Female pleon broad, granulated, with 6 free somites and telson; somite 3 broadest; telson slightly longer than basal width ( Fig. 9C, D ); female vulvae large, without opercular cover, on distal part of sternite 5, opening circular ( Fig. 9E ). Male unknown.

Etymology. Named after locality of the holotype, Selat Sunda, Indonesia.

Remarks. Of the species known in the genus Mariaplax so far, only two species, M. narusei and M. secus Rahayu & Ng, 2014 have a broad, rectangular carapace, which is 1.7 and 1.6 times as broad as long, respectively. Mariaplax sundaica n. sp. resembles M. secus in the broad, rectangular carapace and the absence of a longitudinal groove on the lateral surface of the merus of P4. However, differences can be seen in the broader carapace (1.7 times as broad as long), shorter merus of P4 (3.4 times as long as broad), and relatively broader third maxilliped in M. sundaica n. sp. compared to a slightly narrower carapace (1.6 as broad as long), much longer merus of P4 (4.3 times as long as broad), and relatively narrower third maxillipeds in M. secus . While both M. sundaica n. sp. and M. narusei have a carapace 1.7 as long as broad, M. narusei has a smooth carapace surface (closely-spaced tubercles on M. sundaica n. sp.) and short ambulatory legs with the merus of P4 2.8 times as long as broad (merus of P4 is 3.4 times as long as broad in M. sundaica n. sp.).

Distribution. Selat Sunda, Indonesia

Figures

FIGURE 9. Mariaplax sundaica n. sp., holotype, female (5.3 × 3.1 mm) (MZB Cru 4683). A, overall habitus; B. carapace showing front; C, thoracic sternites and pleonal somites; D, third maxilliped, pterygostomian region, and telson; E, female sternopleonal cavity and vulvae; F, front showing orbit; G, major chela; H, minor chela.

FIGURE 10. Mariaplax sundaica n. sp., holotype, female (5.3 × 3.1 mm) (MZB Cru 4683). A, carapace; B, right third maxilliped;C, pleon; D, major chela; E, minor chela; F, outer view of left P2; G, outer view of left P3; H, outer view of left P4. Scales A, C̅H = 1.0 mm; B = 0.5mm.