Pilumnus acanthosoma Ng, 2000

Komai, Tomoyuki & Motoh, Hiroshi, 2012, The identity of Pilumnus dofleini Balss, 1933 (Crustacea: Decapoda: Brachyura Pilumnidae), with descriptions of three new species from the Western Pacific, Zootaxa 3305, pp. 1-27 : 9-12

Pilumnus acanthosoma Ng, 2000

( Figs 6 , 7 )

Pilumnus acanthosoma Ng, 2000: 303 , figs 3–6; Ng et al. 2008: (list).

Material examined. Paratypes: 1 male (11.6 x 12.6 mm), 1 female (12.9 x 14.9 mm), ZRC 1997.701, Tung-Kang, Kaohsiung County, Taiwan, 100–400 m, commercial trawlers, 5 August 1996, coll. P. K. L. Ng. Non-type: 2 males (12.0 x 13.3, 16.3 x 18.1 mm), ZRC 2001.0100, similar locality, 6 November 2000, coll. P. K. L. Ng; 2 females (12.7 x 14.6, 13.8 x 16.0 mm), CBM-ZC 2860, same locality, 5 August 1996, coll. T. Komai.

Diagnosis. Carapace ( Fig. 6 A, B) transversely subovoid, surface with sparse, relatively long stiff setae, but without covering of very short setae; greatest width across fourth anterolateral spines, about 1.1 times of length; regions clearly defined, slightly elevated, armed with small sharp conical spines, grooves defining regions relatively deep, naked; cardiac region with more than 10 conspicuous spines or tubercles; frontal margin slightly produced, weakly deflexed, separated medially by distinct V-shaped notch; each frontal lobe not markedly divided, with row of unequal spines (most lateral, mesial spines longer than others); inner supraorbital angle with distinct spine directed anterolaterally; supraorbital margin with row of sharp spines, with trace of 2 clefts; anterolateral margin spinose, with 4 principal spines (including spiniform external orbital angle), these anterolateral spines elongated, increasing in size posteriorly, obliquely erect, each with 1 or 2 accessory spinules basally; posterolateral margin almost straight, converging towards posterior margin; posterior part with submarginal row of conspicuous, conical spines; suborbital margin bordered with row of sharp spines, innermost spine prominent, visible in dorsal view; suborbital region with covering of numerous sharp granules; pterygostomial groove smooth, bordered dorsally by row of minute granules; dorsolateral portion of buccal frame with several granules.

Third maxilliped with ischium granular on outer surface; outer surface of merus coarsely granular; outer surface of exopod granular entirely.

Chelipeds ( Figs 6 A, 7A) slightly unequal, slightly dissimilar with right larger than left; surfaces of carpi, chelae bearing sparse longish setae; anterior margins of fused basis-ischium segment with row of sharp granules; merus with 2 distal spines and row of small spines on crested posterodorsal margin; carpus with scattered long spines on dorsal to outer surface (these spines slightly curving forward), inner distal angle produced in prominent spine; palm with relatively strong, acute spines, arranged in 5 or 6 irregular rows on outer surface, inner dorsal margin bluntly carinate with row of spines, ventral surface rounded, having rows of spines; fingers slightly longer than palm, with row of blunt teeth on cutting edges (major) or row of sharply edged, triangular teeth (minor); dactylus with row of tiny spines or sharp granules on dorsal margin extending nearly to tip; outer surface of dactylus with median carina bearing spinules accompanied by shallow sulcus.

Ambulatory legs ( Figs 6 A, 7A) moderately long, relatively slender for genus, bearing sparse short to long stiff setae on margins and surfaces, but lacking covering of short setae; coxa with few acute granules on ventral surfaces; basis-ischium fused segment with some acute granules or spinules on ventral surfaces; merus with single row of acute spines on dorsal margin; ventral margin also each with row of acute spines; outer (posterior) surface smooth in first to third legs, with few spinules in fourth leg; carpus with 2 rows of slender, acute spines on extensor surface; propodus with 2 rows of slender, acute spines on dorsal margin, flexor margin unarmed; dactylus slender, distinctly longer than propodus, unarmed on extensor margin, relatively sparsely setose.

Thoracic sternum ( Fig. 7 B) with scattered stiff setae; fused sternites 1–3 weakly granular; sternites 4–8 with scattered, sometimes spiniform tubercles.

Male abdomen ( Fig. 7 B) with tiny spiniform tubercles on all somites, although becoming less numerous toward sixth somite.

First gonopod sinuous; distal 0.2 noticeably arcuate in lateral or mesial view, slightly directed laterally in ventral view, gradually tapering, bearing row of minute setae not extending to apex (see Ng 2000; fig. 4h–k).

Coloration. Carapace reddish brown to orange in anterior part, posterior part and grooves separating regions whitish. Outer surfaces of chelipeds and ambulatory legs generally reddish brown with scattered white patches. Thoracic sternum and abdomen white. Setae on carapace and appendages golden brown.

Distribution. So far known only from southwestern Taiwan; 100– 400 m.

Remarks. Pilumnus acanthosoma is readily recognizable by the possession of sparse, short to moderately short stiff setae on the surfaces of the carapace and on the outer surfaces of the chelipeds, instead of a covering of very short setae, the strong armature on the carapace, thoracic sternum, abdomen and appendages, and the deep grooves defining regions on the carapace. The ambulatory legs are relatively the most slender among the five species discussed in this study. The male first gonopod of this species is similar in the general shape to those of P. dofleini and P. a r m a t u s n. sp.

Figures

FIGURE 6. Pilumnus acanthosoma Ng, 2000, male (11.6 x 12.6 mm), ZRC 1997.701. A, entire animal, dorsal view; B, carapace, dorsal view.

FIGURE 7. Pilumnus acanthosoma Ng, 2000, male (11.6 x 12.6 mm), ZRC 1997.701. A, entire animal, ventral view; B, thoracic sternum and abdomen, ventral view.