Petrolisthes inermis (Heller, 1862)

Werding, Bernd & Hiller, Alexandra, 2015, Description of a new species of Petrolisthes in the Indo-West Pacific with a redefinition of P. hastatus Stimpson, 1858 and resurrection of P. inermis (Heller, 1862) (Crustacea, Anomura, Porcellanidae), ZooKeys 516, pp. 95-108 : 97-100

Taxon classification Animalia Decapoda Porcellanidae

Petrolisthes inermis (Heller, 1862) Fig. 2

Porcellana inermis Heller, 1862: 424 (partim); 1865: 76, pl. 6, fig. 5.

Petrolisthes inermis ? De Man, 1893: 288, pl. 7, fig.1.

Petrolisthes tenkatei De Man, 1893: 289, pl. 7, figs 2, 2a, 2b.

Petrolisthes sp. n.? De Man, 1902: 69, pl. 23, fig. 37.

Petrolisthes hastatus Nakasone & Miyake, 1971: 5 (partim), pl. 1, B-D.

Type material.

Nicobar Islands: Novara Expedition 1857-59. NHM24237, lectotype, female (ov), CL 6.4 mm × CW 7.0 mm, 23.02.-20.03.1858; NHM24238, paralectotype, 1 male, CL 6.7 mm × CW 6.6 mm, 23.02.-20.03.1858.

Other material examined.

Indonesia. RMNH.CRUS.D.2604, 1 male, Indonesia, Endeh, Flores Island, leg. H. ten Kate, 1891; Measurements: CL 8,5 mm × CW 9,0 mm; RMNH.CRUS.D.1643, 5 males, 2 females (1ov), Indonesia, Endeh, Flores Island, leg. H. ten Kate, 1891; RMNH.CRUS.D.56410, 4 males, Indonesia, Sangihe Island, leg. D.J. Hoedt 1867. Indonesia: Snellius Expedition. RMNH.CRUS.D.56411, 12 males, 3 females (ov), Ternate, beach, 24.09.1929; RMNH.CRUS.D.56412, 1 male, Rambay by Timor, beach and reef, 26-28.11.1929; RMNH.CRUS.D.56413, 1 male, 2 females (ov), Paleleh, Celebes (Sulawesi), beach, 22.08.1929; RMNH.CRUS.D.56414, 1 male, 1 female, (with Bopyridae ), Ende, (Flores), 06.-08.11.1930; RMNH.CRUS.D.56415, ca. 430 specimens, Ende, (Flores), 06.-08.11.1930; RMNH.CRUS.D.56416, 2 males, Ambon, beach and reef 0-2m, 06.05.1930; RMNH.CRUS.D.56417, ca. 80 specimens, Ambon, 11.-17. 09. 1930. Indonesia: Indonesien-Dutch Snellius-II Expedition. RMNH.CRUS.D.56418, 3 males, Sta.4.001, Ambon Bay, near Tawiri, cobble beach to disturbed reef, dead corals, 0-5m, snorkeling, scuba diving, 22. and 30.08.1984. RMNH.CRUS.D.56419, 1 male, Sta.18, Ambon, Hitu, E side of Laha, up to and including Tawiri, littoral, 08.11.1990; RMNH.CRUS.D.56420, 12 males, 6 females (5ov), Ambon, Hitu, W side of Laha, 06.12.1990; RMNH.CRUS.D.56421, 2 males (1 without chelae), 1 female (ov), Ambon, Sta. 36, Paso,(Bugala), littoral collection, 05.12.1990; RMNH.CRUS.D.56422, 1 male, Ambon, Station 1, in front of the house, littoral collection, leg. CHJM Fransen, 06.11.1990. Papua New Guinea. MNHN-IU-2013-9125, 3 males, 1 female (ov), Stn. PM08, 05°15'17.82" - 145°46'38.91", Yabob Village, Gum River, 0-1m, 12.11.2012.

Measurements.

Largest male: CL 11.0 mm × CW 11.0 mm; largest female: CL 8.6 mm × CW 9.0 mm.

Description.

Carapace as broad as long, or somewhat broader than long, evenly rounded at branchial regions, broadest at posterior branchial level; surface covered with faint plications, more accentuated laterally. Front produced, sinuously triangular, rostrum with a moderately deep median sulcus, supraocular angle scarcely produced, depressed by a shallow groove. Orbits shallow, outer orbital edge bluntly produced, forming a shallow lobe with hepatic margin. Epibranchial angle unarmed, marked by a ridge continuing along the mesobranchial margin. Protogastric ridge forming a distinct crest, cervical grooves and regions poorly defined. Lateral walls thickly matted with long, feathered setae, largely concealing the basal parts of the walking legs.

Basal segment of antennular peduncles with faint transverse rugae, anterior margin rounded, with distinct tooth at mesial corner and rounded protuberance at lateral corner.

First movable segment of antenna anteriorly with foliate, square-cut projection with a shallow, forwardly directed tooth; second with a longitudinal granular crest, extending proximally in a rounded tooth, third rounded, unarmed.

Chelipeds sub-equal. Merus with transverse, shallow plications on dorsal surface, anterior margin armed distally with a finger-shaped, granular lobe, fringed with short setae. Carpus slender, highly variable, from about 3 to 4 times longer than broad, dorsal surface covered with low, scale-like granules; anterior margin with 2 shallow teeth, a third one faintly marked or lacking; the proximal tooth normally the largest and acute, the second one smaller and blunt. Posterior margin slightly curved outwards, granules along posterior margin enlarged, forming a crest along the postero-distal margin, extending into a spine-tipped, distal tooth. Chelae large, slender, transversely swollen; outer margin curved on entire length, unarmed; fingers spineless, frequently gaping in larger chela. Gape of fingers with large, dense pubescence, visible from above, sometimes only in one chela, seldom lacking. Ischium of walking legs covered with a pubescence of feathered setae; merus with a single dorsal spine close to the distal edge in L1 and L2, and a fringe of feathered setae on anterior margin; merus of L1 and L2 with a posterodistal spine, sometimes lacking in L2 or in both. Carpus and propodus with a fringe of feathered setae on anterior margin, with scattered feathered and simple setae. Propodus ventrally with distal triplet of movable spinules and one additional spine at mid-distance; dactylus with 3 movable spines on posterior margin.

Variation.

Large specimens normally present more elongate and narrower chelipeds, more variation in the form of the chelipeds than smaller ones, and often exhibit a remarkable heterochely.

Habitat.

Petrolisthes inermis seems to be a shallow water species. According to the material of the Papua New Guinea Expedition and the two Snellius Expeditions in Indonesia the species was collected in the littoral in rocky beaches and on dead corals, in depths of 0-5 m.

Distribution.

Eastern Indian Ocean, Nicobar Islands, Indonesia, Papua New Guinea, New Caledonia.

Remarks.

Some of the original material from the Novara Expedition is deposited in the collections of the Naturhistorisches Museum (NHM) in Vienna. We found two lots labelled as “Syntypus” of Porcellana inermis Heller, 1862. One lot (NHM24237) contained a moderate-sized female, which was selected as lectotype. The other (NHM24238) contained a small male lacking the right chela and two walking legs, and a larger female lacking one cheliped. The small male was selected as paralecto type. The second specimen represents a different species. De Man´s (1893) original specimens of Petrolisthes tenkatei (RMNH.CRUS.D.2604, RMNH.CRUS.D.1643) are deposited in the collections of the Naturalis Biodiversity Center (Leiden). They are labelled as lectotype and paralectotypes of Petrolisthes tenkatei , which is a synonym of Petrolisthes inermis . Judging from the figure of Petrolisthes sp. n. from De Man (1902, fig. 37) this species also corresponds to Petrolisthes inermis , and is therefore included in the synonymy of that species.