Polyonyx obesulus Miers, 1884

Osawa, Masayuki, 2007, Porcellanidae (Crustacea: Decapoda: Anomura) from New Caledonia and the Loyalty Islands, Zootaxa 1548, pp. 1-49 : 36

Polyonyx obesulus Miers, 1884

( Fig. 11 )

Porcellana obesula White, 1847 , 130 (nomen nudum).

Polyonyx obesulus Miers, 1884: 272 , pl. 29, fig. D (type locality: Madgica-Sima (=Sakishima) Islands, Ryukyu Islands). — Johnson, 1958: 108, fig, 4.— Haig, 1964: 378; 1966c: 61; 1979: 132, fig. 20–22; 1992; 321, fig. 17.— Yang & Xu, 1994: 117, fig. 4.

Porcellana (Polyonyx) sp.—de Man, 1888: 424, pl. 19, fig. 1.

Porcellana (Polyonyx) tuberculosa de Man, 1888: 424 (type locality: Amboina, Moluccas, Indonesia).

Polyonyx parvidens Nobili, 1905: 161 (type locality: Persian Gulf).

Polyonyx paucidens Nobili, 1906: 70 , pl. 5, fig. 16.

Material examined. Loyalty Islands. Lifou Island. Santal Bay. Atelier LIFOU. St. 1466 (St. 45), Hunete Bay, 20°46.5’S, 167°06.2’E, 25–45 m, 17 Nov. 2000, 1 male CL 2.6 mm. St. 1457 (St. 67), Ngoni, 20°46.8’S, 167°02.75’E, 5–10 m, 27 Nov. 2000, 1 male CL 2.6 mm.

Remarks. The type locality of Porcellana obesula White, 1847 (nomen nudum) is Madgica-Sima (=Sakishima) Islands, Ryukyu Islands.

Polyonyx obesulus resembles P. biunguiculatus but differs in having a less developed, broad median lobe of the rostrum ( Fig. 11 B; narrow median lobe in P. biunguiculatus , Fig. 9 B) and dactyli of the ambulatory legs, each armed with a single corneous spine on the flexor margin ( Fig. 11 E, F; two spines in P. biunguiculatus , Fig. 9 F–H).

The specimens examined have a proportionally longer carpus of the larger cheliped ( Fig. 11 C), which differs from the original illustrations by Miers (1884, pl. 29, fig. D, d’) as well as figures by Johnson (1958, fig, 4A) and Haig (1979, fig. 20). The male specimens examined also possess low protuberances on the dorsoextensor surface of smaller chela ( Fig. 11 D) and a pair of gonopods. These characters agree with a specimen of P. obesulus from the Nansha Islands reported by Yang & Xu (1994: 117, fig. 4A, C). The elongate carpus of the larger cheliped is also illustrated in the Hong Kong material by Haig (1992: fig. 17B). The specimens of the Loyalty Islands are tentatively referred to P. obesulus until the type material and other specimens can be examined.

As pointed out by Johnson (1958: 96, 112), Polyonyx paucidens Nobili, 1906 is a lapsus calami for P. parvidens Nobili, 1905 . The holotype in the Muséum national d’Histoire naturelle, Paris, is labeled “ Polyonyx paucidens ” (see Haig 1966c). Haig (1966c) concluded that the juvenile female holotype is referred to P. obesulu s because the characters by which Nobili (1906) distinguished P. paucidens from P. obesulu s, including presence of spinules on the flexor margins of the merus and carpus of the chelipeds, are sometimes found in young P. obesulus specimens (see Haig 1964).

Distribution. Indonesia, then westward through Malay Archipelago to Persian Gulf, south to tropical Australia, and northeast to Sakishima Islands; littoral to about 55 m, frequently in sponges and crevices of corals ( Haig 1979, 1992). The specimens examined were collected at depths of 5–45 m in the Loyalty Islands.

Figures

FIGURE 9. Polyonyx biunguiculatus (Dana, 1852), neotype, male, CL 2.8 mm, Loyalty Islands, St. 1462 (A – H); female, CL 2.5 mm, New Caledonia, Koumac (I). A, carapace, and ocular and antennal peduncles, dorsal view; B, rostrum, anterior view; C, larger cheliped, dorsal view; C, third and forth thoracic sternites, ventral view (setae omitted from right side); D, left anterior part of pterygostomial flap, ocular and antennal peduncles, and basal article of antennular peduncle, ventrofrontal view; E, left third maxilliped, ventral view (setae omitted); F, left first ambulatory leg, lateral view; G, same, dactylus and distal part of propodus, lateral view; H, left second ambulatory leg, lateral view; dactylus and distal part of propodus, lateral view; I, right second ambulatory leg, lateral view. Scales equal 1.0 mm.

FIGURE 11. Polyonyx obesulus Miers, 1884, male, CL 2.6 mm, Loyalty Islands, St. 1457. A, carapace, and ocular and antennal peduncles, dorsal view; B, rostrum, anterior view; C, larger cheliped, dorsal view; D, smaller chela, dorsal view; E, right first ambulatory leg, lateral view; F, same, dactylus and distal part of propodus, lateral view. Scales equal 1.0 mm.