Borneosa sarawakensis, Ng & Grinang, 2022

Ng, Peter K L & Grinang, Jongkar, 2022, Establishment of A New Bornean Genus of Gecarcinucidae (Crustacea: Brachyura), with Descriptions of Five New Species., Zoological studies 61 (13), pp. 1-35 : 20-23

Borneosa sarawakensis sp. nov.

( Figs. 15, 16, 22I–L, 23E) urn:lsid:zoobank.org:act:

Material examined: Holotype: male (35.5 × 28.1 mm), 1 female (11.8 × 10.3 mm) ( ZRC 2021.0516), first order stream, primary forest, Sungei Musing, Batang Ai National Park, Sri Aman, Sarawak, Malaysia, coll. J. Grinang et al., 30 January 2015. Paratypes: 1 female (11.8 × 10.3 mm) (ZRC 2021.0517), same data as holotype. Others: 1 male (30.8 × 24.6 mm) (ZRC 2020.0338), station THH19-34, in fast flowing water over bedrock, rocks and gravel, feeder stream to Sungei Mujok, survey up to ca. 800 m upstream, Nanga Sepulau, Kanowit basin in Rejang Basin, 1°40.999'N 112°09.908'E, Sarawak, Malaysia, electrofishing, coll. H.H. Tan et al., 15 October 2019; 3 females (24.6 × 20.9 mm, 25.3 × 21.2 mm, 27.2 × 22.7 mm [with one juvenile crab under pleon]) (ZRC 2020.0336), station DZ-01, along first small stream on right side of Sungei Mujok, upstream from base camp, at night, Lanjak-Entimau National Park, Sarawak, Malaysia, coll. K.O. Chan et al., 12 October 2019; 1 brooding female (30.0 × 24.0 mm) (ZRC 2020.0337), station THH19-33, in clear fast flowing water over bedrock, rocks, gravel, upstream from Nanga Sepulau (ca. 1 km) to Nanga Sepuna, Kanowit basin in Rejang Basin, 1°40.917'N 112 °10.162 ' E, 104 m asl, Sarawak, Malaysia, electrofishing, coll. H.H. Tan et al., 14 October 2019.

Diagnosis: Adult carapace transversely subquadrate, width to length ratio 1.18–1.26 ( Fig. 15A, B); striae on lateral parts of carapace strong ( Fig. 15B); branchial regions gently convex in frontal view ( Fig. 15C, F); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 15C–E); exorbital tooth with outer margin almost entire ( Fig. 15B); epibranchial tooth very low to absent, separated from rest of margin by very low cleft when present ( Fig. 15B), anterolateral margin almost entire ( Fig. 15B); median lobe of posterior margin of epistome obtusely triangular ( Fig. 15C–E); ischium of third maxilliped rectangular ( Fig. 16A); fingers of larger adult male cheliped with gape at base of when closed ( Fig. 16D); P3 and P4 dactyli subequal in length ( Fig. 16F, G); male pleonal somite 6 rectangular, longer than broad ( Fig. 16C); male sternopleonal cavity not prominently anterior, distance between tip of cavity and suture of thoracic sternites 2 and 3 longer than length of thoracic sternite 2 ( Fig. 16B); adult Gl subterminal segment relatively slender; terminal segment subcylindrical, distal half distinctly curved outwards, with distinct rounded tip, 0.30–0.32 times length of subterminal segment, distal opening large, subovate ( Fig. 22I–K); vulvae almost round ( Fig. 23F).

Colour: In life, the carapace is maroon to reddish brown, darker on the anterior parts; the ambulatory legs and chela are olive brown with the ventral surface pale yellow ( Fig. 25B).

Etymology: The species is named after the state of Sarawak.

Remarks: For differences between B. sarawakensis sp. nov. and its closest species, B. kapit sp. nov., see remarks for latter taxon.

Biology: All the habitats in the type locality are feeder streams of the Batang Ai hydroelectric reservoir, on a relatively high gradient, with rocky substrates and fast flowing clear, cold water ( Fig. 25A). The specimens from Lanjak-Entimau Wildlife Sanctuary, Kanowit, were collected from pristine forest streams with shallow water and a rocky substrate. These sites share the same drainage.