Ceratoplax margarita n. sp., a new rhizopine crab (Crustacea: Brachyura: Pilumnidae) from Papua New Guinea, with rediagnoses of C. truncatifrons Rathbun, 1914, and C. fulgida Rathbun, 1914 Author Ng, Peter K. L. Author Clark, Paul F. text Zoosystema 2015 2015-06-30 37 2 323 331 http://dx.doi.org/10.5252/z2015n2a2 journal article 10.5252/z2015n2a2 1638-9387 5155702 urn:lsid:zoobank.org:pub:DF6FC413-9BD1-459B-BC25-FB8F6A0FD339 Ceratoplax margarita n. sp. ( Figs 5 ; 6 ) TYPE MATERIAL . — Holotype : Papua New Guinea , ♂ , 7.9 × 5.2 mm (MNHN-IU-2014-10126), stn DW3663, Open Bay , 04°50’S , 151°39’E , 220-292 m , 23.IX.2010 , Cruise BIOPAPUA, R . V . Alis , coll. S. Samadi & L. Corbari. ETYMOLOGY. — The Latin name, margarita , name alludes to the white, pearl-like appearance of the species. The name is used as a noun in apposition. DIAGNOSIS. — Carapace transversely subovate, width 1.52 × length; dorsal surfaces smooth, glabrous, regions poorly demarcated, H-shaped gastric grooves barely discernible; anterolateral margin strongly convex, entire to weakly dentate with three small clefts, reaching along ⅔ of lateral margin, submarginal parts smooth, not clearly demarcated from posterolateral margin; posterolateral margins gently concave, converging to gently convex posterior carapace margin ( Fig. 5A ). Frontal margin weakly divided into two low subtruncate lobes from dorsal view, gently confluent with supraorbital margin; with low external orbital tooth ( Fig. 5A ). Orbit ovate, small, eyes with small cornea, fused to carapace, immovable ( Fig. 5B ). Posterior margin of epistome gently convex, not clearly divided into lobes ( Fig. 5B ). Anteroexternal angle of merus of third maxilliped with auriculiform structure; exopod stout ( Fig. 6F ). Male thoracic sternum wide, sternites 1 and 2 completely fused to form wide triangular structure; separated from fused sternites 3 and 4 by distinct sinuous suture ( Fig. 5C ). Male abdomen FIG. 5. — Ceratoplax margarita n. sp. , holotype ♂, 7.9 × 5.2 mm (MNHN-IU-2014-10126), Papua New Guinea: A , overall dorsal view; B , frontal view of carapace and chelae; C , anterior thoracic sternum and abdomen. Scale bars: 1.0 mm. FIG. 6. — Ceratoplax margarita n. sp. , holotype ♂, 7.9 × 5.2 mm (MNHN-IU-2014-10126), Papua New Guinea: A , ventral view of right G1; B , dorsal view of right G1; C , ventral view of distal part of right G1; D , dorsal view of distal part of right G1; E , right G2; F , left third maxilliped (setae not drawn). Scale bars:A, B, 0.5 m; C-E, 0.1 mm; F, 1.0 mm. T-shaped; somite 6 rectangular, wider than long; telson triangular, elongate, much longer than somite 6 ( Fig. 5C ). Chelipeds stout, carpus with subdentiform inner angle and tuft of setae, outer angle sharp but not spiniform or dentiform; chela stout, fingers shorter than palm ( Fig. 5A, B ). Ambulatory legs, long; articles slender, unarmed; dactylus of last leg upcurved ( Fig. 5A ). G1 distinctly sinuous, subdistal part hump-like with tapering tip which is gently bent, opening slender ( Fig. 6 A-D). TYPE LOCALITY . — Open Bay, 04°50’S , 151°39’E , Papua New Guinea . DISTRIBUTION. — Known only from the type locality. REMARKS There are many superficial similarities between Ceratoplax margarita n. sp. , C. truncatifrons and C. fulgida . The series of specimens of C. truncatifrons from Indonesia show that the diagnostic characters of this species are quite consistent, notably in the general shape of the carapace ( Figs 1 ; 2 ). Although the proportions change, being relatively broader in larger specimens (e.g., Figs 1A ; 2C ), the shape remains unchanged. The structure of the thoracic sternums is also quite consistent, although the male telsons are slightly more elongate in the larger males ( Fig. 1C ) compared to the more evenly triangular ones in smaller ones ( Fig. 2D, E ). In C. fulgida , the anterolateral margin may appear to be entire ( Figs 3A ; 4H ) or weakly dentate ( Fig. 4I ). Ceratoplax margarita n. sp. can be distinguished from C. truncatifrons and C. fulgida in having its posterolateral margin more distinctly converging towards the posterior carapace margin ( Fig. 5A ) (weakly converging in the other two species; Figs 1A ; 2 A-C; 3A). In addition, the anteroexternal angle of the merus of the third maxilliped of C. margarita n. sp. is auriculiform ( Fig. 6F ), resembling that of C. fulgida ( Fig. 4G ) but different from C. truncatifrons that has the anteroexternal angle prominently elongate ( Fig. 4C ). The sternoabdominal cavity of C. margarita n. sp. reaches to the median part of fused thoracic sternite 3 and 4, at an imaginary line connecting bases of coxae of chelipeds ( Fig. 5C ) (like in C. truncatifrons , Figs 1C ; 2D, E ) but in C. fulgida , it reaches up to two-thirds of fused thoracic sternites 3 and 4, to an imaginary line connecting midpoints of bases of cheliped coxae ( Fig. 3C ). The G1 of C. margarita n. sp. is relatively stout ( Fig. 6A, B ), but is distinctly more slender in C. truncatifrons ( Fig. 4A, B ). In stoutness, the G1 of C. margarita n. sp. looks more like that of C. fulgida but has a small hump on the dorso-subdistal part ( Fig. 6 A-D) (vs margin gently curved without any hump, Fig. 4D, E ).