Kasagia arbastoi, Forges, Bertrand Richer De & Ng, Peter K. L., 2007

Forges, Bertrand Richer De & Ng, Peter K. L., 2007, On a new genus and new species of deep-water spider crab from the Philippines (Crustacea, Decapoda, Brachyura, Majidae), Zootaxa 1644, pp. 59-68 : 61-66

Kasagia arbastoi , new species

( Fig. 1 , 2 A, 3A, C, 4A, C, 5B, C)

Material examined. Holotype: male (12.1 x 8.7 mm) ( NMCR), Balicasag Island, Panglao, Bohol, Philippines, coll. tangle nets, 29 May 2005. Paratypes: 1 male (12.6 x 9.2 mm) ( ZRC), 1 male (11.2 x 7.9 mm) ( MNHN), Balicasag Island, Panglao, Bohol, Philippines, 200–300 m, coll. fishermen, tangle nets, Jun 2002.

Comparative material. Eurynome aspera ( Pennant, 1777) : 6 males ( ZRC 1988.665-670), on sedimentary bottom, 25 m, Rovinj, Croatia, coll. Z. Števčić, 30 July 1986.

Etymology. The species is named after a most astute fisherman, Jo Arbasto, who has helped us obtain many interesting species in the course of our expeditions.

Diagnosis of male holotype. Small-size species (less than 15 mm in carapace length). Ovoid carapace completely covered by rounded, squamiform granules, edges of granules touching each other but their profiles, visible laterally, fungiform. Rostrum small, sharply directed downward, with 2 strong peudorostral spines, diverging, sharp, relatively long, oval cross-section. Eyes round with short peduncle, totally protected inside orbit when retracted; large, flat post-ocular spine; supra-ocular margin forming a regular concave curved eave, separated from base of pseudorostral spine by a fissure, posterior part of eave overlapping postorbital spine; post-orbital spine strong, forming a concavity bordered by setae to receive eye. Hepatic margin with a strong, flattened triangular tooth, separated from post-ocular spine by large gap. Gastric region elevated with 2 large granuliform spines, with long setae but not covering surface. Antenna with first 2 articles fused, unmovable; basal antennal article triangular with narrow longitudinal groove, base of fused basal antennal article with lateral projection extending anteriorly towards post-orbital tooth, flagellum short. Antennular fossae ovoid. Third maxilliped covered by granules, densely setose; ischium rectangular, depressed medially, covered with short setae; merus triangular with longitudinal groove, internal border with rounded expansion anteriorly. Chelipeds very long, about 3 times carapace length; merus cylindrical, longer than other articles in male [females not known], stout, granulated, with 3 rows of blunt spinules; carpus short, narrow proximally, enlarged distally; propodus long, with 10 blunt spinules along upper border; dactylus short, curved, sharp, finely serrulated on internal margin; chelae relatively small, fingers slightly bent from horizontal, tips of sharp fingers crossing when closed. Ambulatory legs (P2-P5) short; meri carinated, other articles setose; lower part of meri covered with setae, upper part glabrous, each with distal tooth separated from main carina; carpus, propodus, dactylus short, strongly setose, almost completely covering surfaces. Male abdomen with 6 free segments and telson, surface covered with tomentum of short setae; first segment narrow distally; telson relatively long, tip pointed, slightly concave laterally. G1 simple, apical part dilated, margin appears folded, no spines or extensive setae present.

Colour in life ( Fig. 1 ). Kasagia arbastoi , is mostly reddish brown dorsally, with the posterior portions lighter in colour. The gastric regions are dark brown, while the regions around the rostrum and orbits are purplish. The meri of the legs are white with regularly arranged reddish-brown spots.

Discussion. In general appearance, and certainly with regards to the long male chelipeds and carapace features, Kasagia arbastoi , new species, most closely resembles some species of Eurynome , especially E. aspera and E. erosa . Other than the differences already discussed for the genera, K. arbastoi has acuminate rostral spines which are relatively short (less than six times the length of the carapace), the meri of the ambulatory legs are dorsally cristate, and the hepatic margin has a flattened triangular plate largely separate from the postorbital lobe. The granulation of the carapace of K. arbastoi superficially resembles Chionognathus granulosa (see Baker 1906: 108, Pl. 1, figs. 3, 3a), but the two differ markedly in all other aspects. The carinated merus of the ambulatory legs of K. arbastoi is similar to that of Chionognathus elegans described from South Africa, but in K. arbastoi there is a large distal tooth after the carina ends, a structure absent on C. elegans . In C. elegans , there are also spines on the lower border of the P5, which are absent in K. arbastoi (see Stebbing 1921: 454, Pl. 108; Barnard 1950: 57, fig. 12d, e).

Kasagia arbastoi was collected from the steep slopes of Balicasag Island in the central Philippines, where the local fishermen have developed a novel way of using tangle nets to collect deep-water molluscs. This rarely used fishing method, in which the nets are set to lie against the steep deep sea cliffs, is the only way to sample this steep habitat. At Balicasag, this method has helped discover many new and interesting species in recent years (e.g. Dromiidae , Dynomenidae : McLay & Ng 2004, 2005; Homolidae : Richer de Forges & Ng 2007a; Homolodromiidae : Ng & McLay 2005; Majidae : Richer de Forges & Ng 2007b; Leucosidae: Komatsu et al. 2005; Galil & Ng 2007; Ng & McLay 2005; Mathildellidae : Ng & Ho 2003; Crosnier & Ng 2004; Calappidae : Ng 2003; Pseudoziidae : Ng & Liao 2002; Goneplacidae : Castro, in press; Vultocinidae : Ng & Manuel-Santos 2007; Stomatopoda: Ahyong, 2004; various taxa: Takeda & Manuel 2000; Takeda & Manuel- Santos, 2007). All this new material obtained from the sampling of the slopes shows that in many cases, rarity is an illusion. Species appear to be rare when their preferred habitats are unknown or because such habitats cannot be sampled effectively (Ng 2006).

Figures

FIGURE 1. Kasagia arbastoi, new species, male paratype (11.2 x 7.9 mm) (MNHN). Colour in life.

FIGURE 2. Overall dorsal views. A, Kasagia arbastoi, new species, male holotype (12.1 x 8.7 mm) (NMCR); B, Eurynome aspera, male (12.4 x 11.5 mm) (ZRC 1988.665).