Sesarmoides microphthalmus, Naruse & Ng, 2007

Naruse, Tohru & Ng, Peter K. L., 2007, On A New Species Of Cavernicolous Crab Of The Genus Sesarmoides Serène & Soh, 1970 (Crustacea: Decapoda: Brachyura: Sesarmidae) From Sulawesi, Indonesia, Raffles Bulletin of Zoology 55 (1), pp. 127-130 : 127-130

Sesarmoides microphthalmus , new species

( Figs. 1 , 2 )

Material examined. – Holotype: male (CL 12.5 mm, CW 14.3 mm) ( MZB 2002.17 ), Gua Marapetang, Kecamatan Barru, Kabupaten Barru, South Sulawesi, Indonesia, coll. C. Rahmadi, 15 Apr.2002.

Paratypes: 1 female (CL 10.5 mm, CW 12.4 mm) ( MZB 2002.0008 ) , 1 male (CL 9.1 mm, CW 10.2 mm), 1 female (CL 9.2 mm, CW 10.6 mm) ( ZRC), same data as holotype .

Comparative material: Sesarmoides jacobsoni ( Ihle, 1912) : 2 males (CL 17.1 mm, CW 18.9 mm; CL 17.0 mm, CW 18.5 mm) ( ZRC 1970.3.1.1), syntypes, Djumblang Cave , Bedojo District, Gunung Sewu, central Java, Indonesia .

Description of male holotype. – Carapace ( Figs. 1 , 2a, b ) trapezoidal, maximum width across base of second ambulatory legs, width 1.12–1.19 times length; dorsal surface uneven, minutely punctate, not setose, regions distinct; front relatively wide, 0.49–0.52 times fronto-orbital width, almost same width as posterior margin of carapace, distinctly deflexed, with wide and rounded median concave, frontal margin slightly bent anteriorly; postfrontal cristae composed of four protuberances, placed transversely between base of peduncle of eyes, median pair wider; mesogastric region divided by inverted Y-shaped groove, with a nodule behind lateral postfrontal crista. Supraorbital margin L-shaped in dorsal view, divided into two cristae near posterior margin of peduncle of eye, anterior crista contiguous with orbit, extending as far as second segment of antenna, forming inner orbital tooth at anterior end; infraorbital margin composed of two granulated ridges, with a line of setae between these ridges. Lateral margin of carapace gently diverging posteriorly, anterolateral margin with three teeth including external orbital angle, first tooth acute, weakly curved anteriorly; second tooth with blunt tip, more curved than first tooth, separated from former tooth by U-shaped cleft; third tooth smallest, separated by small notch, tip of second tooth placed closer to first tooth than third; epibranchial and mesobranchial regions separated by oblique striae, anterolateral region with a nodule near U-shaped notch present between first and second teeth, mesobranchial region sloping outwards, covered with oblique striae. Epistome with median triangular and lateral rounded lobes on posterior margin; branchiostegite covered with reticulate uniform network of short setae. Eyes distinctly reduced, not occupying whole orbit, distal end reaching to outer third of orbit, cornea reduced but pigmented, subdistal width of cornea about half width of base of peduncle in frontal view.

ambulatory coxae, merus to dactylus of third leg 2.5–2.7 times carapace length, meri to propodi with reticulated pattern on dorsal surface, with black fine spines, no mat of setae on inner margin of propodi and dactyli, length to width ratio of meri of second and third legs 2.8–3.3 and 3.0–3.7, respectively, length to width ratio of propodi of second and third legs 3.1– 4.5 and 4.0–4.5, respectively.

Male abdomen ( Fig. 2e ) relatively wide, telson with rounded distal margin. G1 ( Fig. 2f, g ) relatively stout, distal part chitinous, directed outwards at an angle of about 45˚, chitinous part with a small outer lamellar projection, with elongated opening on dorsal face. G2 ( Fig. 2h ) simple, subequal in length to chitinous part of G1.

Colouration. – Live specimens are yellowish-cream overall.

Habitat. – All the specimens were collected from near the cave entrance but were not observed outside it proper. The mouth of the cave has green algae and small plants, indicating that some light can enter. The collector, however, commented that he did not see the species outside the cave. The cornea of the species, while reduced, is clearly not to the extent seen in completely blind species, and is probably able to move outside the cave if need be. However, the elongated legs and reduced pigmentation suggest it does this rarely, if at all. Its Cheliped ( Fig. 2c ) symmetrical in both sexes, male with more robust chela; merus with triangular cross-section, each margin granulated, inner surface with a longitudinal line of pubescence, inner and outer surfaces of merus and dorsal surface of carpus appears reticulated; manus weakly granulated on outer surface, dorsal surface without ridge; fingers of chela with sharp teeth in male, minute teeth in female, with slight gape when fingers closed; tip of fingers corneous, hoof-like, incurved, no line of granules on dorsal surface of movable finger or outer surface of pollex.

Ambulatory legs ( Fig. 2d ) long, third leg longest when stretched laterally, no prominent tufts of setae between habits probably parallel another well known cave species from Borneo, Stygothelphusa bidiensis ( Lanchester, 1900) (Gecarcinucidae) from Borneo ( Ng, 1989; Ng & Yusoff, 1990)

Distribution. – Known only from the type locality thus far.

Etymology. – The name is derived from the Latin words for small eyes, alluding to the reduced cornea of the species.

Remarks. – Serène & Soh (1970) established Sesarmoides for species with a flattened carapace with strongly divergent lateral margins, a swollen and globular antennular segment, a nearly longitudinal antennal peduncle, an epistome with a strong transverse rim and a deep median notch, a narrow frontal margin which is clearly shorter than posterior margin of carapace, and elongated ambulatory legs with the third leg more than twice carapace length. Our new species possesses the above diagnostic characters of the genus except for two features. The relative width of the front of S. microphthalmus , new species, is almost same width as the posterior margin of the carapace, and the lateral carapace margins are relatively less divergent, making the carapace distinctly more quadrate in appearance.

Sesarmoides microphthalmus is clearly closest to S. jacobsoni in its reduced eyes which occupy only a part of the orbit. However, Sesarmoides microphthalmus is easily distinguished from S. jacobsoni by several distinct characters of the carapace, legs and G1 (Table 1).

Figures

Fig. 1 Sesarmoides microphthalmus, new species, holotype male, CL 12.5 mm, CW, 14.3 mm (MZB). Overall view

Fig. 2 Sesarmoides microphthalmus, new species, holotype male, CL 12.5 mm, CW, 14.3 mm (MZB): a, carapace, dorsal view; b, carapace, frontal view; c, chela, right; d, second ambulatory leg, left; e, abdominal segments and telson; f, G1, ventral view; g, G1, dorsal view; h, G2. Scale bars: a–e = 5.0 mm; f–h = 1.0 mm.