Angustopelta, Ng, Peter K. L. & Castro, Peter, 2016

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 55-56

Genus Angustopelta n. gen.

Hephthopelta — Yokoya 1933: 201 (part).— Sakai 1939: 568, 575 (part); 1976: 542 [in key], 551 (part).— Serène 1964a: 239 (part); 1968: 92 [in list] (part).—Ng et al. 2008: 76 [in list] (part).

Type species. Hephthopelta aurita Rathbun, 1932 (gender feminine) Other species included:

Angustopelta cribrorum ( Rathbun, 1932) Angustopelta modesta n. sp.

Angustopelta robusta n. sp.

Diagnosis. Carapace subtrapezoidal, high, wider than long, gently convex dorsally; front bilobed, with shallow median cleft; anterolateral margins arcuate, minutely granular, with sharp tooth or tubercle on anterolateral margin (may be absent). Epistome slightly depressed; broad median lobe with median fissure, semicircular lateral margins. Eye peduncle filling orbit, short, immobile, gently tapering to cornea; cornea reduced, pigmented. Third maxillipeds not filling buccal cavern when closed; merus rounded to quadrate, outer margin rounded, slightly elevated, anteroexternal angle rounded, auriculiform; ischium quadrate to rectangular, about same length or slightly longer than merus. Chelipeds subequal in length, slightly dissimilar in female, heteromorphic in males; fingers of minor chela subcircular in cross-section, not laterally flattened, gently tapering to tip, scissor-like, cutting margins with distinct sharp teeth, largest often most proximal on upper, lower cutting margin. Ventral surface of cheliped merus of both sexes with 4 large teeth (sometimes 3 plus additional small tooth or large tubercle) on outer margin, large round tooth or tubercle near anterior portion of inner margin. Inner margin of carpus with long distal tooth, proximal part rounded to slightly angular. Inner margin of basis-ischium of adult major cheliped gently granuliform. Lower margin of P2 meri may be armed with low teeth, other ambulatory legs unarmed except short granules along margins. P5 dactylus straight. Fused thoracic sternites 1, 2 transversely narrow, short or long; fused thoracic sternites 3, 4 transversely narrow. Male pleon lateral margins of somite 6, fused somites 3‒5 slightly convex; postero-lateral regions slightly swollen; telson proportionally short. Sternopleonal cavity of male deep, press-button for pleonal holding as small, short tubercle posterior to thoracic sternal suture 4/5 near edge or two tubercles, one inside the sterno-pleonal cavity, a second outside cavity. Male thoracic sternite 8 short, quadrate; “supplementary plate” long, subrectangular; structures tightly appressed with most of penis concealed. G1 with stout basal part, distal slender, curved, with short spinules; curved outwards, often extending outside closed pleon (except A. modesta ). G2 short, half or less than half of G1; distal segment short.

Somites of female pleon with convex lateral margins; telson proportionally short. Sterno-pleonal cavity of female deep, vulvae relatively close together, located on outer margins of cavity close to suture 5/6.

Etymology. The name is derived from the arbitrary combination of angustus, Greek for “narrow”, in reference to the proportionally narrow anterior portion of the thoracic sternum.

Remarks. The G1 structure of Angustopelta species (e.g., Fig. 73 A) is very characteristic. The basal part is conspicuously stout and quadrate, the distal part relatively slender, tapering to a subtruncate tip and is prominently curving to one side. In addition, the distal part is partially flattened, with the outer surface relatively flat.

The characteristics and differences between Angustopelta n. gen. and the other genera once treated as part of Hephthopelta s. lato are summarised in Table 2 .

Distribution. Indo-West Pacific region: western Pacific Ocean.

Figures

FIGURE 73. Gonopods of species of Angustopelta n. gen. A, A. aurita, Philippines: male 7.7 × 9.5 mm (ZRC 2015.248); B ‒ E, A. aurita, Philippines: male 9.6 × 11.2 mm (ZRC 2015.250); F ‒ H, A. cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); I, A. cribrorum, Taiwan: male 9.9 × 11.6 mm (ZRC 2015.214). A, B, F, ventral view of left G 1; C, D, G, H, distal part of left G 1; E, I, left G 2. Scales: A, B, E, F, I = 0.5 mm; C, D, G, H = 0.1 mm.