Borneosa bario sp. nov.

(Figs. 10, 11, 21E–H, 23C) urn:lsid:zoobank.org:act: 29131BA7-946F-43E5-986F- BE5B0E72D4B7

Sundathelphusa tenebrosa – Grinang and Nyanti 2007a: 14, pl. 5; Grinang and Nyanti 2007b: 2 (part) (not Sundathelphusa tenebrosa Holthuis, 1979).

Material examined: Holotype: male (29.6 × 23.1 mm) (ZRC 2021.0692), third order stream, downstream, primary forest, Sungei Menalio, Pulong Tau National Park, Bario, 3°34'07.2"N 115°24'22.9"E, 1020 m asl, Sarawak, Malaysia, coll. J. Grinang et al., 18 June 2005 . Paratypes: 1 female (24.3 × 19.3 mm) (ZRC 2021.0693, ex UNIMAS.C.00009), same data as holotype; 1 young male (14.8 × 11.8 mm), 1 young female (19.0 × 15.3 mm) (ZRC 2021.0694, ex UNIMAS.C.00014), third order stream, downstream, primary forest, Sungei Bayuh, Bario, 3°36'36.3"N 115°24'52.9"E, 1070 m asl, Sarawak, Malaysia, coll. J. Grinang et al., 21 June 2005; 1 male (16.2 × 13.4 mm) (ZRC 2021.695), 1 female (15.4 × 13.0 mm) (UNIMAS. C.00026), first order stream, downstream, primary forest Sungei Selipor in Bario, Sarawak, Malaysia, coll. J. Grinang et al., 26 July 2005. 1 male (31.1 × 23.9 mm) (UNIMAS.C.00011), second order stream, downstream, primary forest Sungei Takang in Bario, 3°34'37.1"N 115°23'25.4"E, 1040 m asl, Sarawak, Malaysia, coll. J. Grinang et al., 26 June 2005.

Diagnosis: Adult carapace transversely subovate, width to length ratio 1.26–1.28 (Figs. 10A, B, 11F, H); striae on lateral parts of carapace distinct (Figs. 10B, 11F, H); branchial regions gently convex in frontal view (Fig. 10C); dorsal margin of frontal median triangle contiguous with lateral margins (Fig. 10C–F); exorbital tooth with outer margin almost entire (Figs. 10B, 11F, H); epibranchial tooth distinct, separated from rest of margin by distinct U-shaped cleft (Figs. 10B, 11F, H); median lobe of posterior margin of epistome obtusely triangular (Fig. 10C–E); ischium of third maxilliped subrectangular (Fig. 11A); fingers of adult male cheliped closing along entire cutting margins or with small basal gape (Figs. 11D, E, G); P3 and P4 dactyli subequal in length (Fig. 11J, K); male pleonal somite 6 subquadrate, longer than broad (Fig. 11C); male sternopleonal cavity prominently anterior, distance between tip of cavity and suture of thoracic sternites 2 and 3 distinctly shorter than length of thoracic sternite 2 (Fig. 11B); adult Gl subterminal segment relatively stout; terminal segment subcylindrical, distal half gently curved outwards, tip distinctly truncate, 0.34 times length of subterminal segment, distal opening large, subovate (Fig. 21E–G); vulvae transversely subovate (Fig. 23D).

Colour: In life, the carapace and pereopods are brown to olive brown, with the ambulatory merus grey to light brown; the ventral surfaces being dull yellow (Fig. 24H–J).

Etymology: The name is derived from the area where the crab was found, the Bario Highlands in Sarawak. The name is used as a noun in apposition.

Remarks: Although the Bario Highlands, the type locality of B. bario sp. nov., is inland to the Miri area and Gunong Mulu National Park where B. tenebrosa occurs, B. bario is easily distinguished in having the epibranchial tooth large and well developed with a distinct U-shaped cleft separating it from the rest of the anterolateral margin, even in small individuals (Figs. 10B, 11F, H) (versus tooth very low to obscure, and separated by a shallow narrow cleft at most in B. tenebrosa; Fig. 2B); the dorsal margin of frontal median triangle is contiguous with lateral margins (Fig. 10C–F) (versus separated by a gap or connected by small flattened granules in B. tenebrosa; Fig. 2C– F); the P3 and P4 dactyli subequal in length (Fig. 11J, K) (versus P3 dactylus longer than P4 dactylus in in B. tenebrosa; Fig. 2G, H); and the G1 terminal segment is proportionately stouter and shorter (Fig. 21E–G) (versus more elongate and slender in adult B. tenebrosa; Fig. 20I–K).

The epibranchial tooth of B. bario is well-developed, a character shared with B. niah sp. nov. and B. serrata sp. nov. The tooth is distinct and cleft deep even in small subadult specimens of B. bario . From B. niah, B. bario can easily be separated by epibranchial tooth being more pronounced with the cleft deep (Fig. 10B, 11F, H) (versus tooth smaller and cleft shallow in B. niah; Fig. 8B); the third maxilliped ischium being proportionately longer (Fig. 11A) (versus distinctly shorter in B. niah; Fig. 9A); and the G1 terminal segment is proportionately stouter and shorter in adult males (Fig. 21E–G) (versus terminal segment more slender and longer in B. niah; Fig. 21A–C). From B. serrata, B. bario can be distinguished in having the outer margin of the exorbital tooth entire (Fig. 10B) (versus gently serrated in B. serrata; Fig. 17B); the ischium of the third maxilliped is proportionately longer (Fig. 11A) (versus clearly shorter in B. serrata; Fig. 18A); and the G1 subterminal segment is relatively stouter (Fig. 21E–G) (versus slenderer in B. serrata; Fig. 22M–O).

The fingers of the major chela of the holotype male do not obviously gape when closed (Fig. 11D) but that of a slightly larger paratype male shows a distinct small gape (Fig. 11G). This indicates that the presence of a gape is likely size related.

Biology: All specimens were collected from small streams with waters tea-coloured or crystal clear, fast flowing (range: 0.35–1.34 m /s), cold (19.5–21.5°C), and acidic or slightly alkaline (pH 4.68–7.66) (see Grinang and Nyanti 2007a b). The crabs were found underneath rocky substrates under shaded canopy.