Henicoplax eriochir, Castro & P. K. L. Ng, 2010

CASTRO, PETER & NG, PETER K. L., 2010, Revision of the family Euryplacidae Stimpson, 1871 (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 2375 (1), pp. 1-130 : 59-61

Henicoplax eriochir n. sp.

( Figs. 21A–F ; 24A–C )

Goneplax maldivensis — Stephensen 1946: 171 [Persian Gulf].

Type material. Male holotype, 5.2 mm × 8.8 mm ( MNHN-B12511 ; Figs. 21A–D , 24 A–C ), 1 ovigerous female paratype, 5.4 mm × 8.9 mm ( MNHN-B12511 ; Fig. 21E, F ), 1 female paratype, 4.2 mm × 7.1 mm ( MNHN-B12511 ) .

Type locality. Persian Gulf, unknown location.

Material examined. Persian Gulf. No data: male holotype, 5.2 mm × 8.8 mm, 1 ovigerous female paratype, 5.4 mm × 8.9 mm, 1 female paratype, 4.2 mm × 7.1 mm ( MNHN-B12511 ) .

Diagnosis. Chelipeds with conspicuous tomentum ( Fig. 21A, B ). Somite 2 of male abdomen shorter than somite 3, with relatively large portion of thoracic sternite left exposed by closed abdomen ( Fig. 21C ). G1 with acuminate apex ( Fig. 24A, B ) (see also Table 3).

Description. Carapace ( Fig. 21A ) hexagonal, transversely elongated, wider than long (1.7 wider than long in male holotype), anterolateral borders nearly straight, dorsal surface without clear indication of regions; front wide, lacking median notch. Transverse depression (postorbital ridge) below each orbit extending from anterolateral tooth, becoming progressively shallower before disappearing at the level of distal portion of eye peduncle. One short, triangular, obtuse anterolateral tooth posterior to triangular, anteriorly oriented outer orbital tooth; plumose setae along posterolateral borders. Orbits long ( Fig. 21A, B, E ), longer than front (1.2 frontal width); slightly sinuous, thin supraorbital border lacking notches ( Fig. 21A ); suborbital border sinuous, with broad median lobe, inner suborbital tooth absent ( Fig. 21B, E ); eye peduncles long (0.6 frontal width), much longer than corneas (1.8 times cornea length in paratype); large, spherical corneas.

Basal antennal article slightly mobile, orbital hiatus closed excluding antennal flagellum from orbit.

Posterior margin of epistome lobular; lateral lobes large, with straight margins, separated from median portion by deep fissure; median portion with 2 broadly rectangular lobes separated by shallow cleft. Anterior margin of endostome well demarcated from buccal cavern, endostomial ridges low. Pterygostomian region smooth. Third maxillipeds ( Fig. 21B, E ) completely closing buccal cavern; ischium rectangular with deep submedian line; merus relatively square in shape, anteroexternal margin of merus auriculiform; exopod long, reaching to just before anterior edge of merus with long flagellum.

Cheliped fingers moderately slender, slightly curved in male holotype ( Fig. 21 A, B ), slightly longer than swollen propodus, dorsal margin of dactylus with microscopic tubercles, distal portion light in colour. Dense tomentum of long, plumose setae along proximal third to half of lower (ventral) margin of dactylus ( Fig. 21A, B ); smaller clump of tomentum on distal end of propodus immediately below dactylus; dense tomentum on inner margin of carpus, distal, inner margin of merus. Inner (dorsal) margin of carpus with small triangular tooth. Dorsal, ventral margins of ambulatory legs (P2–P5) smooth, with long, sparse simple setae; dactyli long, slender; P5 merus proportionally short, ventral margin slightly curved, distal end does not reach anterolateral tooth when folded against carapace; P5 propodus (1.8 mm long, 0.9 mm wide in largest female paratype), proportionally stout, subcylindrical, inner margin fringed with long, plumose setae; outer margin with scattered long, simple setae; P5 dactylus proportionally slender (1.8 mm long, 0.3 mm maximum in largest female paratype), inner margin fringed with scattered long, simple plus plumose setae.

Thoracic sternum ( Fig. 21D, F ) wide, thoracic suture 2/3 complete, convex; 3/4 deep, short, interrupted; 4/5, 6/7, 7/8 interrupted, 5/6 complete; median groove on thoracic sternites 7, 8. Sterno-abdominal cavity of male deep, nearly reaching anterior margin of sternite 4, anterior extremity rounded ( Fig. 21B, D ). Press-button of male abdominal-locking mechanism as very small tubercle near thoracic suture 4/5 ( Fig. 21D ).

Male abdomen narrow, slender, transversely narrow (T-shaped), lateral margins of somites 4–6 abruptly narrowing from somite 3 to narrow, pointed telson ( Fig. 21B, C ); somite 3 reaching inner margins of P5 coxae, large portion on each side of thoracic sternite 8 left exposed by closed abdomen ( Fig. 21C ), somite 2 transversely much shorter than somite 3. G1 ( Fig. 24A, B ) long, slender, sinuous, acuminate apex, with relatively few, small denticles; G2 ( Fig. 24C ) less than one-third of G1, straight, apex with 2 processes: one long, tip obtuse; second much shorter, tip obtuse. Male genital opening (gonopore) coxal; coxo-sternal disposition of long penis, protected by concave posterior portion of thoracic sternite 7 ( Fig. 21D ).

Vulva ( Fig. 21F ) ovoid, extending across anterior portion of sternite 6 close to median axis of thorax, sternal suture 6/7 deflected; covered by soft membrane, sternal vulvar cover absent.

Colour pattern. Unknown.

Etymology. From erios or erion, Greek for “wool”, and cheir, Greek for “hand”, as a noun in apposition, in reference to the tomentum of plumose setae on the anterior margins of the cheliped propodus and merus.

Remarks. Henicoplax eriochir n. sp. is described as new for specimens collected from the Persian Gulf and deposited in the MNHN, and clearly different from H. nitida and its other congeners ( Table 3).

The second abdominal somite of the male holotype of the new species is much shorter than the third abdominal somite and thus a large portion on each side of thoracic sternite 8 is left exposed by the closed abdomen ( Fig. 21C ). This is unique among three of its congeners, where the thoracic sternite 8 is covered by the closed abdomen because the second somite is only slightly shorter than the third ( Table 3). In the remaining species, H. trachydactylus n. sp., the abdomen of the only male known is missing (see below).

Most probably belonging to H. eriochir n. sp. are specimens that Stephensen (1946: 171) incorrectly identified as “ Goneplax maldivensis Rathbun, 1902 ”. His specimens, collected from soft sediments in relatively shallow water (13–23 m) from three locations in the Persian Gulf, were described as having a “great tuft of setae on the inner side” of the base of the fingers, a character neither observed in the holotype of Rathbun’s species (see above) nor mentioned in Rathbun’s description or figures ( Rathbun 1902: 124, figs. 3, 4), but which is diagnostic of H. eriochir n. sp. Goneplax Leach, 1814 , actually belongs in the Goneplacidae , and it was amended to receive four mostly Atlantic species (see Castro 2007: 176).

The G2 of one of Stephensen’s males was described as being a quarter of the G1 length and a male abdomen that “agrees excellently with Rathbun’s fig”, which shows a narrow and slender abdomen. Stephensen’s specimens, although not examined, clearly belong to an undescribed species of Henicoplax n. gen.

The record of “ Goneplax maldivensis ” from Indonesia ( Tesch 1918: 183, pl. 9, fig. 1) does not belong to Henicoplax n. gen. (see remarks for H. maldivensis below), and the same probably applies to other specimens collected by T. Mortensen in Indonesia, identified as “ Goneplax maldivensis ” by T. Odhner and deposited at ZMUC ( Stephensen 1946: 171).

Distribution. Only known from the Persian Gulf. Depth: 13–23 m ( Stephensen 1946).

Figures

FIGURE 21. Henicoplax eriochir n. sp.; A–D, male holotype (5.2 mm × 8.8 mm) (MNHN-B12511), Persian Gulf; E, F, ovigerous female paratype (5.4 mm × 8.9 mm) (MNHN-B12511), Persian Gulf. A, overall view; B, E, ventral views of carapaces; C, posterior portion of male thoracic sternum and abdomen; D, male sterno-abdominal cavity; F, female thoracic sternum and vulvae. Abbreviations: a1–a3 = male abdominal somites 1, 2, 3, respectively; cx5 = coxa of fifth pereopod (P5); es7 = episternite 7; G1 = first male pleopod; G2 = second male pleopod; mg = median groove; p = penis; s4– s8 = thoracic sternites 4 to 8, respectively; tm = tuft of tomentum on cheliped merus; v = vulva.

FIGURE 24. Gonopods of Henicoplax species. A–C, Henicoplax eriochir n. sp., male holotype (5.2 mm × 8.8 mm) (MNHN-B12511), Persian Gulf; D–F, Henicoplax maldivensis (Rathbun, 1902), male holotype of Goneplax maldivensis Rathbun, 1902 (4.8 mm × 7.4 mm) (MCZ 6695), Maldives, Addu Atoll; G, H, Henicoplax nitida (Miers, 1879), male (2.8 mm × 4.2 mm) (ZRC 2008.1358), Hong Kong; I–K, Henicoplax pilimeles n. sp., male holotype (4.2 mm × 6.8 mm) (ZRC 1984.7739–7740), Thailand, Andaman Sea, Phuket I. A, B, D, E, G, H, I, J, right G1, dorsal view; C, F, K, left G2, dorsal view. Scale bars: A, G, I, 0.5 mm; B, C, D, F, H, 0.2 mm; J, K, 0.1 mm; E, 0.05 mm.