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: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 , 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.

Figures

Fig. 15. Borneosa sarawakensis sp. nov., holotype male (35.5 × 28.1 mm) (ZRC 2021.0516), Batang Ai, Sarawak. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, frontal median triangle, eyes, epistome, antennae and antennules; E, F, different views of frontal part of cephalothorax.

Fig. 16. Borneosa sarawakensis sp. nov., holotype male (35.5 × 28.1 mm) (ZRC 2021.0516), Batang Ai, Sarawak. A, left third maxilliped; B, anterior male thoracic sternum and pleon; C, male pleon; D, outer view of chelae; E–H, right P2–P5, respectively, all to same scale.

Fig. 22. A–D, Borneosa kapit sp. nov., paratype male (23.5 × 19.1 mm) (ZRC 2021.0518), Belaga, Sarawak; E–G, B. kapit sp. nov., holotype male (37.4 × 28.4 mm) (SMF 48750), Rajang River, Sarawak; H, B. kapit sp. nov., paratype male (35.8 × 28.0 mm) (ZRC 2021.0521), Kapit, Sarawak; I– L, B. sarawakensis sp. nov., holotype male (35.5 × 28.1 mm) (ZRC 2021.0516), Batang Ai, Sarawak; M–P, S. serrata sp. nov., holotype male (25.5 × 22.0 mm) (ZRC 2006.57), Sungei Pangean, Kalimantan Utara. Scale bars: A, D, E, H, I, L, M, P = 1.0 mm; B, C, F, G, J, K, N, O = 0.5 mm.

Fig. 23. Female thoracic sternum and vulvae. A, Borneosa tenebrosa (Holthuis, 1979), female (30.8 × 24.6 mm) (ZRC 1989.3420), Gunong Mulu National Park, Sarawak; B, B. aspera (Ng & Stuebing, 1989), female (44.1 × 33.1 mm) (ZRC 2014.845), Temburong, Brunei; C, female (39.8 × 31.2 mm) (ZRC 2021.0840), Barito, Kalimantan Tengah; D, B. bario sp. nov., paratype female (24.3 × 19.3 mm) (ZRC 2021.0693), Bario, Sarawak; E, B. kapit sp. nov., paratype female (40.6 × 31.4 mm) (ZRC 2021.0521), Kapit, Sarawak; F, B. sarawakensis sp. nov., female (27.2 × 22.7 mm) (ZRC 2020.336), Lanjak-Entimau, Sarawak.

Fig. 25. A, type locality of B. sarawakensis sp. nov., Sungei Musing, first order stream feeding Batang Ai reservoir, Sri Aman, Sarawak; B, B. sarawakensis sp. nov., holotype male (35.5 × 28.1 mm) (ZRC 2021.0516), Batang Ai, Sarawak (freshly preserved); C, B. kapit sp. nov., paratype male (32.3 × 25.6 mm) (ZRC 2021.0520), Sungei Lebau, Pelagus, Kapit, Sarawak (freshly preserved).