Geosesarma ambawang, Ng, Peter K. L., 2015

Ng, Peter K. L., 2015, Semiterrestrial crabs of the genus Geosesarma De Man, 1892 (Crustacea, Brachyura, Sesarmidae) from western Borneo, Indonesia, with descriptions of three new species, Zootaxa 4048 (1), pp. 37-56 : 43-46

Geosesarma ambawang sp. nov.

( Figs. 8–10 )

Material examined. Holotype: male (11.5 × 10.7 mm) ( MZB Cru 4390), in hill forest with sandy soil, 80–150 m asl, Bukit Wangkan, northeast of Gunung Ambawang , south of Pontianak , 0°22'S 109°17'E, Kalimantan Barat, Indonesia, coll. Y. Kho, March 2015. Paratypes: 1 female (9.4 × 8.7 mm) ( MZB Cru 4391), 2 males (11.9 × 11.0 mm, 9.3 × 8.8 mm), 1 female (10.5 × 9.9 mm) ( ZRC 2015.0453), same data as holotype.

Diagnosis. Carapace quadrate, slightly wider than long, width to length ratio 1.06–1.08, lateral margins subparallel ( Fig. 8 A, B); dorsal surface with well-defined regions, anterior regions densely covered with small rounded, flattened granules ( Fig. 8 B); front deflexed, frontal lobes broad with gently convex margins; postfrontal, postorbital cristae prominent ( Fig. 8 B, C); external orbital tooth triangular, directed obliquely, outer margin gently convex, tip extending beyond lateral margin ( Fig. 8 B). Merus of third maxilliped subovate, subequal in length to ischium; exopod without trace of flagellum ( Fig. 9 A). Outer surface of palm of adult male covered with small rounded granules; dorsal margin of dactylus with 11 or 12 tubercles (distal one smallest), each with pectinated tip ( Fig. 8 E, F). Ambulatory legs with relatively slender merus with sharp subdistal spine on dorsal margin, surfaces slightly rugose ( Figs. 8 A, 9C). Male abdomen triangular; somite 6 not wide, with gently convex lateral margins; telson semicircular ( Figs. 8 D, 9B). G1 relatively stout, subdistal part of outer margin with distinct angled humplike arch, just before distal pectinated part; pectinated distal part elongate from lateral view, subspatuliform from marginal view, with small median cleft ( Fig. 9 D–J).

Colour. Adult males have the anterior half of the dorsal surface of the carapace dark brown to reddish-brown in life, with the posterior half cream or grey; with the chelipeds bright red and the ambulatory legs reddish-brown ( Fig. 10 A, B). The ventral surfaces are orangish-yellow to red ( Fig. 10 B). In smaller specimens and females, the demarcation of the two colours on the dorsal surface of the carapace is less distinct and more irregular ( Fig. 10 D).

Etymology. The species is named after the type locality, Gunung Ambawang . The name is used as a noun in apposition.

Ecology. The species is found in the forest floor near streams. It has also been observed to climbing shrubs and small trees at night ( Fig. 10 C, D) (Y. Kho, pers. comm.).

Remarks. See remarks for G. pontianak sp. nov. (below).

Figures

FIGURE 8. Geosesarma ambawang sp. nov., holotype male (11.5 × 10.7 mm) (MZB Cru 4390), Pontianak, Kalimantan Barat, Borneo. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, ventral view of cephalothorax showing thoracic sternum and abdomen; E, F, outer view of right chela.

FIGURE 9. Geosesarma ambawang sp. nov., holotype male (11.5 × 10.7 mm) (MZB Cru 4390), Pontianak, Kalimantan Barat, Borneo. A, left third maxilliped; B, male abdominal somites 1 – 6 and telson; C, left second ambulatory leg; D, left G 1 (ventral view); E, left G 1 (ventral view); F, distal part of left G 1 (ventral view); G, distal part of left G 1 (dorsal view); H, distal part of left G 1 (subdorsal view); I, J, distal part of left G 1 (mesial view); K, left G 2. All structures (except C) denuded. Scales: A – E, K = 1.0 mm; F – J = 0.5 mm.

FIGURE 10. Geosesarma ambawang sp. nov., colours in life. A, B, non-type male (12.5 × 11.8 mm); C, D, specimens climbing shrubs in situ. Specimens not preserved, photographs by Y. Kho.