Alox rugosum (Stimpson, 1858)

Galil, Bella S. & Ng, Peter K. L., 2015, Leucosiid crabs from Papua New Guinea, with descriptions of eight new species (Crustacea: Decapoda: Brachyura), Zootaxa 4027 (4), pp. 451-486 : 455

publication ID	https://doi.org/ 10.11646/zootaxa.4027.4.1
publication LSID	lsid:zoobank.org:pub:3B32D183-45BA-41F9-82A9-C9C108D53899
DOI	https://doi.org/10.5281/zenodo.6102229
persistent identifier	https://treatment.plazi.org/id/8870B305-E335-4C13-9699-FF478DBF8A9A
treatment provided by	Plazi
scientific name	Alox rugosum (Stimpson, 1858)
status

Treatment

Alox rugosum (Stimpson, 1858) View in CoL

( Figs. 2 View FIGURE 2 C, D, 7A–G, 8B, D–K)

Material examined. 1 male (7.3 mm) (MNHN-IU-2013-8854), 1 female (8.0 mm) (MNHN-IU-2013-17888), stn PR69, Rempi Area, south of lagoon inside bay, 05°01.6'S 145°48.1'E, 2–15 m, 20.11.2012; 1 male (5.8 mm) ( ZRC 2015.267), stn PB12, Kranket I., west side, 05°11.8'S 145°48.8'E, 7–15 m, 11.11.2012; 1 immature female (5.9 mm) ( ZRC 2015.268), stn PD19, Alexishafen, south Megas Islet, 05°05.4'S 145°48.5'E, 3–10 m, 13.11.2012; 1 female (10.0 mm) (MNHN-IU-2013-17896) stn PD 57, Gosern I., 05°09,4'S 145°48,3'E, 1–4 m, 29.11.2012.

Description. Carapace ( Fig. 7A View FIGURE 7. A, C, E, F –G) laterally expanded, 1.5 times as wide as long. Carapace irregularly rimmed, dorsal surface prominently sculpted, pitted, irregularly covered with coalesced flattened granules, resembling coral rubble. Front narrow, produced, upcurved, bilobed, medially deeply pitted. Anterior margin of carapace vertical. Antennule well developed, basal antennular article operculiform, rugose, entirely sealing subovate antennular fossa. Antennae folded in orbital hiatus without gap. Orbits small, rounded, visible in dorsal view; ocular peduncle nearly seals orbit when retracted. Third maxillipeds concealing buccal cavity, closely set with flattened granules ( Fig. 8 View FIGURE 8. A B); merus with pointed apex, outer margin convex, surface with median shallow depression; ischium twice as long as merus along inner margin.

Subhepatic region with narrow groove parallel to anterior margin of carapace, fungiform granules inserted in groove, margin with obtuse, granular, facet medially, visible in dorsal view. Lateral margins of carapace subquadrate, swollen, forming granular rim. Posterolateral margin with granular angular facet submedially. Posterior margin slightly produced, narrow, bilobate. Postfrontal median longitudinal ridge of irregular width. Bottom of irregular depression between marginal rim, swollen branchial regions lined with fungiform granules. Branchial regions swollen, irregularly pitted. Granule-lined irregular grooves separate cardiac, intestinal regions from branchial regions. Intestinal region swollen. Branchiostegal region covered with obsolete granules externally, large fungiform granules interspaced with small rounded granules interiorly.

Chelipeds ( Fig. 7 View FIGURE 7. A, C, E, F E) subequal, robust, covered with flattened granules. Cheliped merus with large tubercle distally on posterior margin; palm inflated, granular, distally pitted; fingers 1.5 as long as palm; dactylus with longitudinal rows of closely spaced granules on outer surface; pollex, wider than dactylus, with carinate ventral margin; cutting edges with minute teeth. Ambulatory legs stout, short, closely granular, diminishing in size posteriorly; meri with single granular row dorsally, 2 rows ventrally; propodi with row of conic granules ventrally; dactyli slender, longer than propodi, studded with conic granules, terminating in incurved cornute claw ( Fig. 8 View FIGURE 8. A D).

Thoracic sternites with large, granule-lined fossae. Male, female abdominal cavity deep, reaching buccal cavity. Male abdomen with granular interrupted grooves on either side of median ridge, telson triangular, elongated ( Fig. 8 View FIGURE 8. A E). Gl straight along entire length, dorsoventrally flattened, distally slightly dilated, setose, apex pointed, with slit-like opening ( Fig. 8 View FIGURE 8. A F, G). Female abdominal somites 1, 2 narrow, horizontal, distinctly granular; somites 3–6 fused, shield-like, divided into 3 parts by 2 shallow submedian furrows; telson laciniate. Vulvae large, nearly rectangular; directed vertically.

Colour in life. Carapace and legs bone-coloured with pale orange blotches, female abdomen with 2 pairs of brown dots ( Fig. 2 View FIGURE 2 C, D).

Remarks. We refer the present specimens to A. rugosum (Stimpson, 1858) (type locality: “Loo Choo”, see discussion Tan & Ng 1995: 131) with doubt. In the general appearance of the carapace, with dorsal surface prominently sculpted, pitted, and irregularly covered with coalesced flattened granules, it is closest to this species. The present specimens nevertheless differ slightly from most of the specimens previously referred to A. rugosum (cf. Tan & Richer de Forges 1993: fig. 4C, D; Tan & Ng 1995: fig. 12D, pl. 6D) in possessing a more distinct depression medially on the dorsal frontal surface; the male abdomen has more distinct granular interrupted grooves on either side of the median ridge, the rounded obtuse angle on hepatic margin with a shallow oval depression is not distinct, and the male telson is proportionately shorter. The specimens from Papua New Guinea most closely resemble in carapace form those previously reported from Gisser I. near Ceram in the Moluccas, Indonesia and figured as A. rugosum by Tan & Ng (1995: pl. 7A, B). Considering the substantial variation in the carapace form in A. rugosum , as well as the similarity of the G1 structures of the present specimens ( Fig. 8 View FIGURE 8. A F, G, I, J) to those figured for A. rugosum s. str. (cf. Tan & Ng 1995: fig. 12H, I), it would be premature to recognize the present material as a new species.

Geographical distribution. This species is known only from Japan to New Caledonia ( Tan & Ng 1995). New record for Papua New Guinea.