Henicoplax pilimeles, 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 : 65-68

Henicoplax pilimeles n. sp.

( Figs. 24I–K ; 25A–G ; 27A, B )

Heteroplax nitidus — Serène & Lohavanijaya 1973: 74, 98, pl. 18, figs. B–D [Andaman Sea coast of Thailand]. — Serène & Soh 1976: 23 (as H. nitidas [sic]), fig. 22, pl. 6, Fig. D (part) [Andaman Sea coast of Thailand]. [not Henicoplax nitida ( Miers, 1879) ]

Heteroplax nitida — Naiyanetr 1998: 78; 2007: 90 [Andaman Sea coast of Thailand]. — Ng & Davie 2002: 378 [Andaman Sea coast of Thailand]. [not Henicoplax nitida ( Miers, 1879) ]

Type material. Male holotype, 4.2 mm × 6.8 mm ( Figs. 24I–K ; 25A–E ); 1 female paratype, 4.1 mm × 6.7 mm ( ZRC 1984.7739 – 7740 ) ( Fig. 25F, G ); 1 male paratype, 3.9 mm × 5.8 mm ( ZMUC CRU-9965 ); 1 female paratype, 3.8 mm × 5.7 mm ( ZMUC CRU-10068 ); 1 male paratype, 4.3 mm × 6.3 mm ( NHM 1988.34 ) .

Type locality. Thailand, Andaman Sea coast, west coast of Phuket I.

Material examined. Myanmar [= Burma]. Gulf of Martaban , E. W. Bates coll.: 1 male paratype, 4.3 mm × 6.3 mm ( NHM 1988.34 ) .

Thailand. Andaman Sea , Thai-Danish Expedition: stn.1008–5, 08°43’N, 98°11’E, 20 m, 08.01.1966: 1 male ( ZMUC CRU-9963 ) . – Stn. 1010–7, 08°45’N, 98°07’E, 29 m, 09.01.1966: 1 male, 3.3 mm × 4.9 mm ( ZMUC CRU-9964 ) . – Stn. 1018–2, 09°27’N, 98°016’E, 15 m, 12.01.1966: 1 female, 3.8 mm × 5.7 mm ( ZMUC CRU-10068 ) . – Stn. 1018–9, 09°27’N, 98°16’E, 15 m, 12.01.1966: 1 male ( ZMUC CRU-10067 ) . – Stn. 1019–7, 09°28’N, 98°07’E, 21 m, 12.01.1966: 1 male ( ZMUC CRU-10071 ) . – Stn. 1019–1, 09°28.2’N, 98°07.2’E, 21 m, 12.01.1966: 1 male paratype, 3.6 mm × 5.4 mm ( ZMUC CRU-10069 ) . – Stn. 1019–4, 09°28’N, 98°07’E, 20 m, 12.01.1966: 1 male, 1 male parasitized by sacculinid, 1 female parasitized by sacculinid ( ZMUC CRU-10070 ) . – Stn. 1179, 08°08’24”N, 98°16’48”E, sandy mud, 18 m, 09.03.1966: 1 male paratype, 3.9 mm × 5.8 mm ( ZMUC CRU-9965 ) .

Phuket I., west coast, off Airport Beach , 20 m, muddy sand, B. Chatananthawaj coll., 07.04.1981: male holotype, 4.2 mm × 6.8 mm, 1 female paratype, 4.1 mm × 6.7 mm ( ZRC 1984.7739 – 7740 ) .

Diagnosis. Inner margins of cheliped carpi with simple setae. G1 apex transversely cut ( Fig. 24I, J ) (see Table 3).

Description. Carapace ( Fig. 25A ; Serène & Soh 1976: fig. 22C, as Heteroplax nitidus ) hexagonal, transversely elongated, wider than long (1.6 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 each eye peduncle ( Fig. 25A ). One short, triangular, obtuse anterolateral tooth posterior to triangular, anteriorly oriented outer orbital tooth. Orbits long ( Fig. 25A, B, F ), almost as long as front (0.9 frontal width); slightly sinuous, thin supraorbital border lacking notches; suborbital border sinuous, with broad median lobe, inner suborbital tooth absent ( Fig. 25B, F ); 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. 25B, F ; Serène & Soh 1976: fig. 22E, as H. nitidus ) completely closing buccal cavern; ischium rectangular with deep submedian line; merus relatively square in shape, anteroexternal angle angular, rounded; exopod long, reaching to just before anterior edge of merus with long flagellum.

Cheliped fingers moderately slender, slightly longer than swollen propodus, dorsal margin of dactylus with microscopic tubercles, distal portion light in colour. Inner margin of carpus with small triangular tooth plus sparse, long, simple setae. Dorsal, ventral margins of ambulatory legs (P2–P5) smooth, with long, sparse simple setae; dactyli long, slender; P5 ( Fig. 27A, B ; Serène & Soh 1976: fig. 22D, as H. nitidus ) merus proportionally short, ventral margin slightly curved, distal end does not reach anterolateral tooth when folded against carapace; P5 propodus (1.6 mm long, 0.8 mm wide in one of 3 detached P5 from type material), proportionally stout, subcylindrical, inner margin fringed with many long, plumose setae; outer margin with scattered long, plumose setae; P5 dactylus proportionally slender (1.8 mm long, 0.3 mm maximum width in holotype), inner margin fringed with many long, plumose setae.

Thoracic sternum ( Fig. 25G ) 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. 25B ). Press-button of male abdominal-locking mechanism as very small tubercle near thoracic suture 4/5.

Male abdomen narrow, slender, transversely narrow (T-shaped), lateral margins of somites 4–6 abruptly narrowing from somite 3 to narrow, pointed telson ( Fig. 25B ; Serène & Soh 1976: fig. 22A, as H. nitidus ); somite 3 reaching inner margins of P5 coxae ( Fig. 25C ), anterior tip of outer margin of somite 3 locking under outer posterior edge of thoracic sternite 7 ( Fig. 25D ), only small portion of thoracic sternite 8 left exposed on each side by closed abdomen, somite 2 transversely shorter than somite 3. G1 ( Fig. 24I, J ; Serène & Soh 1976: fig. 22B, Bʹ, as H. nitidus ) long, slender, slightly sinuous, transversely cut apex, with relatively few, small denticles; G2 ( Fig. 24K ) less than one-third of G1, straight, apex with 2 processes: one long, tip acute; 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. 25E ).

Vulva ( Fig. 25G ) 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 pilos, Greek for “hairy”, and melos, Greek for “limb”, as a noun in apposition, in reference to the many long, plumose setae on the inner margin of the P5 propodus and dactylus that is diagnostic of the new species.

Remarks. The new species is described from material collected by the 1966 Thai Danish Expedition to the Andaman Sea, which was reported by Serène & Lohavanijaya (1973: 74) and Serène & Soh (1976: 23) as belonging to Heteroplax nitida Miers, 1879 (= Henicoplax nitida ), plus additional material collected from the same region. Although closely related to H. nitida , the inner margins of the P5 propodus and dactylus are bordered by many long, plumose setae ( Fig. 27A, B ; Serène & Soh 1976: fig. 22D, as H. nitidus ), a character that separates the new species from H. nitida and its four congeners, where the long setae are absent ( Table 3).

It can also be differentiated by the transversely cut apex of its G1 ( Fig. 24I, J ), which is acuminate in its congeners except in H. nitida ( Fig. 24G, H ) and H. maldivensis ( Fig. 24D, E ). The G1 of H. pilimeles n. sp., although having a transversely cut apex as in H. nitida , can be differentiated from the latter by a different distribution of spinules on the distal portion of the G1. Differences observed in the material on hand may be due to differences in size. The distribution of spinules on the G1 of H. pilimeles n. sp. illustrated by Serène & Soh (1976: fig. 22B, Bʹ, as H. nitidus ), however, does resemble more than that of the H. nitida drawn here. The transversely cut apex of both species is not very distinct in Serène & Soh’s (1976) figure.

Distribution. Andaman Sea coasts of Myanmar [= Burma] and Thailand. Depth: 15– 29 m.

Figures

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.

FIGURE 25. Henicoplax pilimeles n. sp.; A–E, male holotype (4.2 mm × 6.8 mm) (ZRC 1984.7739–7740), Andaman Sea, Phuket I.; F, G, female paratype (4.1 mm × 6.7 mm) (ZRC 1984.7739–7740), Andaman Sea, Phuket I. A, dorsal view of carapace; B, F, ventral views of carapaces; C, posterior portion of male thoracic sternum and abdomen; D, abdomen locking into sternum; E, sterno-abdominal cavity, G1, and penis; G, 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; mg = median groove; p = penis; pr = postorbital ridge; s4–s8 = thoracic sternites 4 to 8, respectively; v = vulva.

FIGURE 27. A, B, Henicoplax pilimeles n. sp.; male holotype (4.2 mm × 6.8 mm) (ZRC 1984.7739–7740), Thailand, Andaman Sea coast; C–F, Henicoplax trachydactylus n. sp.; male holotype (3.4 mm × 5.3 mm) (MNHN-B29236), Madagascar; G–I, Heteroplax transversa Stimpson, 1859, male (5.8 mm × 9.5 mm) (ZRC 2008.1356), Hong Kong. A, B, P5; C, D, right G1, dorsal view; E, right G2, dorsal view; F, left cheliped, dorsal view; G, H, left G1, dorsal view; I, left G2, dorsal view. Scale bars: A, B, F, 1.0 mm; C, G, 0.5 mm; D, 0.2 mm, E, H, I, 0.1 mm.