Ceratoplax truncatifrons Rathbun, 1914 (Figs 1; 2; 4 A-C)

Ceratoplax truncatifrons Rathbun, 1914: 147. — Tesch 1918: 205, pl. 12, fig. 1. — Serène 1968: 91 (list). — Ng 1987: 78, 88 (discussion). — Ng et al. 2008: 143 (list).

TYPE MATERIAL. — Holotype: Philippines, ♂, 7.0 × 4.2 mm, (USNM 46399), stn 5206, off western Samar, Badian Island, north 27° east, 5.75 miles, 11°31’40”N, 124°42’40”E, 32 fms, coll. R. V. Albatross, 14.IV.1908.

NON- TYPE MATERIAL. — 1 ♂, 5.2 × 3.3 mm, (NNM Cru D-2164), stn 193, on reef, Sanana Bay, east coast of Sula Besi, east of Sulawesi, coll. M. Webber, Siboga Expedition, 13-14.IX.1899; 1 ♂, 4.0 × 2.5 mm, 1 ♀ ovig., 3.9 × 2.4 mm, 3 ♀, 5.6 × 3.5 mm, 4.3 × 2.7 mm, 4.7 × 3.0 mm, 1 damaged ♀, (NNM-ZMA Crust De 203018), stn 193, on reef, Sanana Bay, east coast of Sula Besi, east of Sulawesi, coll. M. Webber, Siboga Expedition, 13 Sanana Bay, east coast of Sula Besi, east of Sulawesi 14.IX.1899.

DIAGNOSIS. — Carapace transversely subovate, width 1.52- 1.67 × length; dorsal surfaces smooth, glabrous, regions poorly demarcated, H-shaped gastric grooves barely discernible; anterolateral margin strongly convex, entire, reaching along ⅔ of lateral margin, submarginal parts smooth, not clearly demarcated from posterolateral margin; posterolateral margins almost straight, gradually converging to gently convex posterior carapace margin (Figs 1A; 2 A-C). Frontal margin weakly divided into two low subtruncate lobes from dorsal view, gently confluent with supraorbital margin; with low external orbital tooth (Figs 1A, B; 2 A-C). Orbit ovate, small, eyes with small cornea, fused to carapace, immovable (Fig. 1B). Posterior margin of epistome gently convex, not clearly divided into lobes (Fig. 1B). Anteroexternal angle of merus of third maxilliped strongly, acutely auriculiform; exopod stout (Fig. 4C). 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 or gently concave (towards buccal cavity) suture (Figs 1C; 2D, E). Male abdomen T-shaped; somite 6 rectangular, distinctly wider than long; telson triangular, longer than somite 6 (Figs 1C; 2D, E). 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 (Figs 1A, D, E; 2 A-C). Ambulatory legs, long; articles slender, unarmed; dactylus of last leg upcurved (Fig. 2A, C). G1 distinctly sinuous, subdistal part hump-like with slender tapering tip that is prominently bent, opening large (Fig. 4A, B).

TYPE LOCALITY. — Western Samar, Badian Island, Philippines.

DISTRIBUTION. — Known only from the type locality and Sulawesi.

REMARKS

The series of specimens from Sulawesi are smaller than the holotype male but agree in all the key carapace, third maxilliped, thoracic sternal and ambulatory leg characters of C. truncatifrons. The G1 of the smaller male (4.0 × 2.5 mm, NNM-ZMA Crust De 203018) is similar in shape to the holotype except it is slightly more bent, but is otherwise identical.

The carapace proportions of this species increase with size, and smaller specimens have reduced carapace width to length ratios. The general shape of the carapace, however, remains almost the same (Fig. 2 A-C). See discussion for Ceratoplax margarita n. sp.