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

publication ID	https://doi.org/ 10.6620/ZS.2022.61-13
DOI	https://doi.org/10.5281/zenodo.8055972
persistent identifier	https://treatment.plazi.org/id/CF2E433D-3C21-FFB5-FF48-FEE3350BFBBA
treatment provided by	Valdenar
scientific name	Borneosa sarawakensis
status	sp. nov.

Treatment

Borneosa sarawakensis View in CoL sp. nov.

( Figs. 15 View Fig , 16 View Fig , 22I–L View Fig , 23E View Fig ) urn:lsid:zoobank.org:act:1A80E5BF-EB74-42B0-AF74-98E5023A91FA

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 GoogleMaps , upstream from base camp, at night, Lanjak-Entimau National Park GoogleMaps , 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 View Fig ); striae on lateral parts of carapace strong ( Fig. 15B View Fig ); branchial regions gently convex in frontal view ( Fig. 15C, F View Fig ); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 15C–E View Fig ); exorbital tooth with outer margin almost entire ( Fig. 15B View Fig ); epibranchial tooth very low to absent, separated from rest of margin by very low cleft when present ( Fig. 15B View Fig ), anterolateral margin almost entire ( Fig. 15B View Fig ); median lobe of posterior margin of epistome obtusely triangular ( Fig. 15C–E View Fig ); ischium of third maxilliped rectangular ( Fig. 16A View Fig ); fingers of larger adult male cheliped with gape at base of when closed ( Fig. 16D View Fig ); P3 and P4 dactyli subequal in length ( Fig. 16F, G View Fig ); male pleonal somite 6 rectangular, longer than broad ( Fig. 16C View Fig ); 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 View Fig ); 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 View Fig ); vulvae almost round ( Fig. 23F View Fig ).

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 View Fig ).

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 View Fig ). 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.