Borneosa kapit, 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 : 17-19

publication ID	https://doi.org/ 10.6620/ZS.2022.61-13
DOI	https://doi.org/10.5281/zenodo.8055970
persistent identifier	https://treatment.plazi.org/id/CF2E433D-3C22-FFB0-FEE5-FBC335E7FE9A
treatment provided by	Valdenar
scientific name	Borneosa kapit
status	sp. nov.

Treatment

Borneosa kapit View in CoL sp. nov.

( Figs. 12–14 View Fig View Fig View Fig , 19D View Fig , 22A–H View Fig , 23D View Fig ) urn:lsid:zoobank.org:act:432F792E-60B3-4AD8-9AF1-D00BD8D087E7

Material examined: Holotype: male (37.4 × 28.4 mm) ( SMF 48750 View Materials ), Balui River , Rejang River, 2°44.616'N 114°4.565'E, Sarawak, Malaysia, coll. A. Leek, 11 November 1982 GoogleMaps . Paratypes: 2 males (20.6 × 16.9 mm, 12.8 × 9.9 mm) (UNIMAS.C.00039), first order stream, downstream, logged forest Sungei Pap in Belaga, 2°38'08.1"N 114°26'16.6"E, 535 m asl, Sarawak, Malaysia, coll. J. Grinang et al., 10 September 2007; 3 males (23.5 × 19.1 mm, 19.1 × 16.6 mm, 13.7 × 11.2 mm), 1 female (22.1 × 18.1 mm) (ZRC 2021.0518), second order stream, upstream, logged forest Sungei Belepu in Belaga, 2°37'22.4"N 114°24'55.3"E, 497 m asl, Sarawak, Malaysia, coll. J. Grinang et al., 11 September 2007; 1 male (12.0 × 11.0 mm), 1 juvenile) (UNIMAS.C.00045), second order stream, midstream, logged forest Sungei Belepu in Belaga, 2°37'26.0"N 114°25'02.4"E, 450 m asl, Sarawak, Malaysia, coll. J. Grinang et al., 11 September 2007; 1 juvenile (UNIMAS.C.00051), first order stream, downstream, logged forest Sungei Sunan in Belaga, 2°39'30.8"N 114°11'11.0"E, 476 m asl, Sarawak, Malaysia, J coll. J. Grinang et al., 9 September 2007; 1 male (21.9 × 18.7 mm) (ZRC 2021.0519), 2 females (27.3 × 23.4 mm, 12.4 × 10.9 mm) (UNIMAS.C.00101), second order stream, logged over forest Sungei Simalajau, Kapit, Sarawak, Malaysia, bought from Teresang Market, Kapit, J. Grinang , 14 April 2016; 1 male (37.5 × 29.4 mm), 1 female (29.5 × 23.5 mm) (ZRC 2021.0690), first order stream, Nanga Benin, Pelagus, Kapit, Sarawak, Malaysia, coll. J. Grinang et al., 6 September 2016; 1 male (32.3 × 25.6 mm) (ZRC 2021.0520), first order stream, logged over forest Sungei Lebau, Pelagus, Kapit, Sarawak, Malaysia, coll. J. Grinang et al., 11 December 2015; 2 males (35.8 × 28.0 mm, 35.8 × 28.6 mm), 2 females (40.6 × 31.4 mm, 36.9 × 29.0 mm) (ZRC 2021.0521), 3 males (35.8 × 28.6 mm, 35.3 × 28.0 mm, 35.3 × 28.3 mm, 36.9 × 28.7 mm), 2 females (36.6 × 29.9 mm, 28.5 × 23.6 mm) (UNIMAS.C.00102), second order stream, Sungei Yong, Kapit, Sarawak, Malaysia, sent by M.B. Sadar, 8 February 2020.

Diagnosis: Adult carapace transversely subovate, width to length ratio 1.20–1.32 ( Figs. 12A, B View Fig , 14 View Fig ); striae on lateral parts of carapace strong ( Fig. 12B View Fig ); branchial regions convex in frontal view ( Fig. 12C, F View Fig ); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 12C–E View Fig ); exorbital tooth with outer margin almost entire ( Fig. 12B View Fig ); epibranchial tooth low to absent, separated from rest of margin by low cleft when present ( Figs. 12B View Fig , 14 View Fig ); median lobe of posterior margin of epistome obtusely triangular ( Fig. 12C–E View Fig ); ischium of third maxilliped subrectangular ( Fig. 13A View Fig ); fingers of larger adult male cheliped with gape at base of when closed ( Fig. 13E View Fig ); P3 and P4 dactyli subequal in length ( Fig. 13G, H View Fig ); male pleonal somite 6 rectangular, longer than broad ( Fig. 13C 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. 13B View Fig ); adult Gl subterminal segment relatively stout; terminal segment subconical, distal half slightly curved outwards, tapering gradually to rounded tip, 0.30–0.33 times length of subterminal segment, distal opening relatively small, round ( Fig. 22A–C, E–G View Fig ); vulvae almost round ( Fig. 23E View Fig ).

Colour: In live, carapace and pereopods orange to light brown, darker on centre of carapace; with ventral surface pale yellow ( Fig. 25C View Fig ).

Etymology: The name is derived from the town of Kapit in the upper part of the Rejang River, where the species occurs. The name is used as a noun in apposition.

Remarks: Borneosa kapit sp. nov. and B. sarawakensis sp. nov. bear a close resemblance, but can easily be separated by several characters. Adult B. kapit have a carapace which is usually wider in proportions (width to length ratio 1.20–1.32, Fig. 12B View Fig ) (versus more quadrate in B. sarawakensis , with the width to length ratio 1.18–1.26; Fig. 15A View Fig ); the epibranchial tooth is small but still usually visible, and even when low, is with rare exceptions, demarcated from the anterolateral margin by a shallow cleft ( Figs. 12B View Fig , 14 View Fig ) (versus epibranchial tooth not visible with the anterolateral margin appearing entire in B. sarawakensis ; Fig. 15B View Fig ); the branchial regions in adult males are relatively higher and appear more inflated in the frontal view ( Fig. 12C View Fig ) (versus with regions relatively lower and less convex in B. sarawakensis ; Fig. 15C View Fig ); the G1 terminal segment has the median part less distinctly bent, with the distal part more elongate with a more tapering tip and the opening proportionately smaller ( Fig. 22A– C, E–G View Fig ) (versus median part distinctly bent with the distal part ending in a rounded tip with a wide opening in B. sarawakensis ; Fig. 22I–K View Fig ). Significantly, while both species are from the Rejang drainage, B. kapit is from the headwaters of the river to the eastern part of Sarawak while B. sarawakensis is on the highlands on the western part of the drainage.

The good series of specimens of B. kapit shows that the degree of variation at the species level is not substantial. The carapace of smaller specimens is proportionately less wide, appearing more subquadrate and the convexity of the branchial regions also less pronounced. The size of the epibranchial tooth varies slightly, but it is always distinct ( Fig. 14 View Fig ). As for the G1, in smaller specimens, the terminal segment is slightly slenderer with a slightly larger distal opening ( Fig. 22A–C View Fig ) compared to the condition in larger adults ( Fig. 22E–G View Fig ).

Biology: The known habitat of the species are small streams flowing through secondary forests or logged over forest, under a partly shaded or complete canopy. The waters are clear, fast flowing, and cold, with the substrates mainly composed of pebbles and cobblestones. The species is occasionally sold at the Teresang Market in Kapit which had been collected from Sungei Similajau (UNIMAS.C.00101), a stream which feeds the main Rejang river.