Hephthopelta Alcock 1899

Genus Hephthopelta Alcock, 1899

Hephthopelta Alcock, 1899: 76; 1900: 327.— Tesch 1918: 202 [in key], 233.— Serène 1964a: 239.—Ng et al. 2008: 76 [in list].— De Grave et al. 2009: 32 [in list].

Type species. Hephthopelta lugubris Alcock, 1899 (gender feminine) Other species included:

Hephthopelta occidentalis n. sp.

Diagnosis. Carapace subtrapezoidal, strongly globose, only slightly wider than long; front bilobed, with shallow to well-defined median cleft; anterolateral margins arcuate, minutely granular, entire or with small tubercle. Epistome slightly depressed; median lobe of posterior margin distinctly broad, with deep median fissure, semicircular lateral margins. Eye peduncle filling orbit, distinctly short, gently tapering to cornea, immobile; cornea reduced, pigmented. Third maxillipeds fill buccal cavern; merus subquadrate to elongated, outer margin nearly straight, anteriorly flattened, anteroexternal angle rounded; ischium ovate to elongated, slightly longer than merus. Chelipeds subequal in length, slightly dissimilar in female, heterochelous in males; fingers of minor chela distinctly flattened laterally, broad throughout most of length, shear-like, cutting margins with low, broad teeth. Ventral surface of cheliped merus with 3 large teeth (sometimes additional small tooth or large tubercle) on outer margin in both sexes, inner margin unarmed. Inner margin of carpus with long distal tooth, short proximal part rounded to dentiform. Inner margin of basis-ischium of adult major cheliped gently granuliform. Inner margin of basis-ischium of adult major cheliped gently granuliform (Fig. 42 G). Meri of P2, P3 with short teeth, meri of other ambulatory legs with microscopic granules, unarmed. P5 dactylus straight to gently curved. Fused thoracic sternites 1, 2 transversely narrow, high, triangular; fused thoracic sternites 3, 4 transversely narrow. Male pleon with lateral margins of somite 6, fused somites 3‒5 nearly straight; postero-lateral regions prominently swollen; telson proportionally short. Sterno-pleonal cavity of male deep, press-button for pleonal holding as small, short tubercle posterior to thoracic sternal suture 4/5 near edge of sterno-pleonal cavity. Male thoracic sternite 8 distinctly short, quadrate; “supplementary plate” short, rectangular; structures tightly appressed with most of penis concealed. G1 with stout basal part, distal part tapering, with short spinules. G2 longer than G1; distal segment long, evenly broad throughout length to tip. Somites of female pleon with convex lateral margins; telson proportionally short, narrow (unknown in H occidentalis). Sterno-pleonal cavity of female deep, vulvae widely separated, on outer margins of cavity close to suture 5/6.

Remarks. Hephthopelta was established by Alcock (1899) for one species, H. lugubris, from the Indian Ocean. At least ten more species have since been added over the years to the genus (Ng et al. 2008). Of these, all are from the Indo-West Pacific region except for Hephthopelta superba Boone, 1927, described from the western Atlantic and now placed in Deltopelta n. gen. (see above).

Examination of the good series of “ Hephthopelta ” specimens on hand shows that the 10 Indo-West Pacific species can be separated into six distinct groups on the basis of the carapace form, eyestalks, structures of the third maxillipeds, chelipeds, ambulatory legs, male thoracic sternum, gonopods, and vulvae. We here recognise six genera: Hephthopelta s. str. (for H. lugubris Alcock, 1899, and H. occidentalis n. sp.), Angustopelta n. gen. (for H. aurita Rathbun, 1932, H. cribrorum Rathbun, 1932, A. modesta n. sp. and A. robusta n. sp.), Chinommatia n. gen. (for H. cavimanus Rathbun, 1914, C. bicuspida n. sp., H. littoralis Tesch, 1918, H. bruuni Serène, 1964, and C. turpis n. sp.), Notopelta n. gen. (for H. mortenseni Serène, 1964), Statommatia n. gen. (for H. apta Rathbun, 1914, S. granulosa n. sp., H. knudseni Serène, 1964, and H. pubescens Chen, 1987) and Tenagopelta n. gen. (for T. pacifica n. sp., T. potens (Davie & Richer de Forges, 2013), and T. brachyphallus n. sp.).

The six genera are all very distinct, easily distinguished by a suite of characters associated with the morphology of the carapace, chelipeds, ambulatory legs, thoracic sternum, male pleon, gonopods, and vulvae (Table 2). Hephthopelta s. str. is closest to Tenagopelta n. gen. because of the rounded form of its carapace and prominently inflated globose appearance when viewed frontally (e.g., Fig. 24 A). The G2 of members of both genera also have well-developed distal segments and are longer than the G1. Members of both genera are also found in deep waters with the former occurring in much greater depths (exceeding 500 m). Compared to Hephthopelta s. str., Tenagopelta n. gen. has mobile eyestalks (immobile in Hephthopelta s. str.); a relatively wider thoracic male sternum (notably sternites 1‒4) but also evident in females (Figs. 54 F; 88C) (distinctly narrower in Hephthopelta s. str., e.g., Figs. 52 A; 91A); the epistome is relatively narrow with a triangular median lobe and sinuous lateral margins with marked fissures) (e.g., Fig. 26 F) (relatively broad, truncated and nearly rectangular with the lateral margins semicircular without fissures in Hephthopelta s. str., e.g., Fig. 24 A); the merus of the third maxilliped is more quadrate (e. g., Fig. 33 G) (subovate in Hephthopelta s. str., e.g., Fig. 31 A); the base of the basal segment of the G2 is distinctly elongated (e.g., Fig. 79 O) (short and rounded in Hephthopelta s. str., e.g., Fig. 71 M); and the distal segment of the G2 is distinctly narrowed medially with the proximal part wider than the distal part (e.g., Fig. 79 E) (G2 distal segment is of uniform width in Hephthopelta s. str., e.g., Fig. 71 E). There are also several other characters that separate the two genera but they may prove to be more species-specific when more species are discovered in the future: the teeth on the inner margin of the cheliped merus are typically shorter in Tenagopelta n. gen. (Fig. 42 I) than in Hephthopelta (Fig. 42 G) and male pleonite 6 relatively narrower (e.g., Fig. 54 F) than in Hephthopelta (e.g., 52A) with the swollen area of postero-lateral regions of somite 3‒5 less marked in Tenagopelta n. gen. (e.g., Fig. 61 E) than in Hephthopelta (e.g., Fig. 59 A).

The remaining species previously placed in Hephthopelta may be placed in two major groups, both with G2s distinctly shorter than the G1 and the distal segment of the G2 poorly developed. One group has immobile eyestalks that are completely immobile in their orbits, the ischium and merus of the third maxilliped are short and quadrate and the G2 is short, half or less than half the length of the G1 (Angustopelta n. gen. and Statommatia n. gen.). The other group has mobile eyestalks, the ischium and merus of the third maxilliped are more elongated, and the G2 is about three-quarters the length of the G1 (Chinommatia n. gen. and Notopelta n. gen.).

The two genera with immobile eyestalks are easily distinguished by the form of their thoracic sterna and gonopods. One genus (Angustopelta n. gen.) has a relatively narrow anterior male thoracic sternum (sternites 1‒4) that is also evident in adult females (e.g., Fig. 52 D); the female sterno-pleonal cavity is relatively deep, with the vulvae on the steep outer margin of the sterno-pleonal cavity (e.g., Fig. 91 B); and the G1 is stout and medially bent (e.g., Fig. 73 A). The second genus (Statommatia n. gen.) has a relatively narrower anterior male thoracic sternum (sternites 1‒4) also evident in adult females (e.g., Fig. 54 B); the female sterno-pleonal cavity is relatively shallow, with the vulvae mesial in the flat portion of thoracic sternite 6 (e.g., Fig. 91 E); and the G1 is more slender, with the distal half almost lanceiform and straight (e.g., Fig. 77 A).

Inner margin of major Gently granuliform Gently granuliform (e.g., Gently granuliform (e.g., With long prolongation Gently granuliform (e.g., Gently granuliform (e.g., cheliped basis-ischium in (e.g., Fig. 42 G) Fig. 42 H) Fig. 42 J, K) visible from dorsal view Fig. 42 M, N) Fig. 42 I) adults (Figs. 15 G; 42L)

……continued on the next page Character Hephthopelta s. str. Angustopelta n. gen. Chinommatia n. gen. Notopelta n. gen. Statommatia n. gen. Tenagopelta n. gen. Fingers of minor chela Distinctly laterally Subcircular in Subcircular in Subcircular in cross-section, Subcircular in Subcircular in

flatteneđ, broađ cross-section, not cross-section, not not đistinctly laterally cross-section, not cross-section, not throughout most of đistinctly laterally đistinctly laterally flatteneđ, gently tapering to đistinctly laterally đistinctly laterally length; shear-like, cutting flatteneđ, gently tapering flatteneđ, gently tapering tip; scissor-like, cutting flatteneđ, gently flatteneđ, gently tapering margins with low, broađ to tip; scissor-like, cutting to tip; scissor-like, cutting margins with đistinct sharp tapering to tip; to tip; scissor-like, cutting teeth (e.g., Fig. 40 E) margins with đistinct margins with đistinct teeth (Fig. 45 B) scissor-like, cutting margins with đistinct

sharp teeth (e.g., Fig. sharp teeth (e.g., Fig. margins with đistinct sharp teeth (e.g., Fig.

41D) 43B) sharp teeth (e.g., Fig. 47 B)

45D)

The group with mobile eyestalks also contains two genera (Chinommatia n. gen. and Notopelta n. gen.), separated by the form of their eyestalks, thoracic sterna, and chelipeds. Chinommatia n. gen. has an eye peduncle that is evenly subcylindrical in cross-section (e.g., Fig. 25 B); a proportionately wider anterior male thoracic sternum (sternites 1‒4) that is also evident in adult females (e.g., Fig. 53 A); and the basis-ischium of the male major cheliped does not have an elongated process (e.g., Fig. 14 B). In contrast, Notopelta n. gen. has the median part of the eye peduncle distinctly constricted and dorso-ventrally flattened, appearing reniform (Fig. 25 G); a proportionately broader anterior male thoracic sternum (sternites 1‒4) (Figs. 53 F); and the male major cheliped basis-ischium has a markedly long hook-like process (e.g., Fig. 42 L).

Distribution. Indo-West Pacific region: Indian and western Pacific oceans.