Henicoplax maldivensis ( Rathbun, 1902 ) CASTRO, PETER & NG, PETER K. L., 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 : 61-63

Henicoplax maldivensis ( Rathbun, 1902) , new combination

( Figs. 22A–E ; 24D–F )

Goneplax maldivensis Rathbun, 1902: 124 , figs. 3–5 [ Maldives]. — Guinot 1969b: 518 [discussion]. — Castro 2007: 686, 687 [in list].

not Goneplax maldivensis — Stephensen 1946: 171. (= Henicoplax eriochir n. sp.)

“? [ Goneplax ] maldivensis ” Rathbun, 1902 — Guinot 1971: 1081 [in list].

Otmaroplax maldivensis Števčić 2005: 134 [nomen nudum]

“ Heteroplax ” maldivensis — Ng et al. 2008: 78, 79 [in list].

not Goneplax maldivensis — Tesch 1918: 183, pl. 9, fig. 1 [ Indonesia]. (? = Goneplacoides marivenae Komatsu &

Takeda, 2003)

Type material. Male holotype, 4.8 mm × 7.4 mm ( MCZ 6695 ) ( Fig. 22A–E ) .

Type locality. Maldives, Gan I., Addu Atoll, 20 fathoms [37 m] .

Material examined. Maldives. Gan I., Addu Atoll, A. Agassiz coll., 5.01.1902, 37 m: male holotype, 4.8 mm × 7.4 mm ( MCZ 6695 ) .

Diagnosis. Chelipeds without tomentum. Apex of G1 slightly transversely cut ( Fig. 24D, E ) (see also Table 3).

Remarks. The possible inclusion of Goneplax maldivensis Rathbun, 1902 , in the Euryplacinae was first suggested by Guinot (1969b: 511, 518), who later ( Guinot 1971: 1081) included the species (as “? [ Goneplax ] maldivensis Rathbun, 1902 ”) in a list of goneplacid crabs under Autres Euryplacinae (attribution générique à préciser). Števčić (2005: 133) placed the species under Otmaroplax in a list of new genera incertae sedis, but it is a nomen nudum because no diagnosis was given (see Castro 2007: 178; Ng et al. 2008: 78, 79). Castro (2007: 686, 687) formally included the species among the Euryplacidae . Ng et al. (2008: 78, 79) recognised its placement as an independent genus in the Euryplacidae and referred to it as “ Heteroplax ” maldivensis .

Henicoplax maldivensis is very close to H. nitida , and a comparison of the holotypes of both species shows only small differences. The outer orbital angle and the anterolateral teeth of the small male holotype of H. maldivensis ( Fig. 22A, B ) are slightly more acute than those of the larger female holotype of H. nitida (6.1 mm × 9.3 mm; Fig. 23A ). Although it is possible that these differences are due to size and/or sex, the wide geographical distance separating both populations suggests that both species are distinct, even if the material currently available is scant. There are also some small differences in the size and distribution of the denticles in the G1 of the two species ( Fig. 24D, E for H. maldivensis ; Fig. 24G, H for H. nitida ) but these may be again due to differences in the size of the specimens.

Material from the Persian Gulf identified by Stephensen (1946: 171) as “ Goneplax maldivensis ”, which only agreed in some respects with Rathbun’s figures and those by Tesch (1918: 183, pl. 9, fig. 1) belong instead to Henicoplax eriochir n. sp. (see above). Tesch’s (1918) Indonesian (Kai Is.) specimen is clearly not H. maldivensis , lacking a postorbital ridge and having much shorter eye peduncles and a wider male abdomen. The specimen is now destroyed but Tesch’s (1918) figures show that it belongs to a goneplacid close to Goneplacoides marivenae (Komatsu & Takeda, 2003) (see Castro 2007: 696).

Colour pattern. Unknown.

Distribution. Only known from the Maldives, Indian Ocean. Depth: shallow subtidal to at least 37 m.

Figures

FIGURE 22. Henicoplax maldivensis (Rathbun, 1914); male holotype of Goneplax maldivensis Rathbun, 1902 (4.8 mm × 7.4 mm) (MCZ 6695). A, dorsal view of carapace; B, third maxillipeds, anterior portion of male thoracic sternum and abdomen; C, orbit and suborbital border; D, posterior portion of male thoracic sternum and abdomen; E, male sternoabdominal cavity, G1, and penis. Abbreviations: a1–a3 = male abdominal somites 1, 2, 3, respectively; cx5 = coxa of fifth pereopod (P5); es7 = episternite 7; G1 = first male pleopod; p = penis; s5–s8 = thoracic sternites 5 to 8, respectively.

FIGURE 23. Henicoplax nitida (Miers, 1879); female holotype of Heteroplax? nitidus Miers, 1879 (6.1 mm × 9.3mm) (NHM 78.11), Straits of Korea. A, overall view; B, third maxillipeds; C, frontal view showing orbits and antennae; D, female thoracic sternum and vulvae. Abbreviations: mg = median groove; s4–s7 = thoracic sternites 4 to 7, respectively; 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.