Borneosa brachyphallus (Ng, 2015)

(Figs. 6, 7, 19C, 22Q–T)

Sundathelphusa brachyphallus Ng, 2015: 494, figs. 1, 2, 7A–E.

Material examined: Holotype: male (27.1 × 22.0 mm) (MZB Cru 4396), Liang Hintan, Hulu Sungei Barito, 0°27'33"N 115°01'1.0"E, 222–250 m asl, Kalimantan Tengah, Indonesia, coll. C. Rahmadi, 16 June 2004. Paratype: 1 male (29.3 × 23.4 mm, chelipeds missing) (ZRC 2015.0460), same data as holotype. Others: 1 male (26.1 × 21.8 mm), 2 females (39.8 × 31.2 mm, 35.2 × 27.6 mm) (ZRC 2021.0840), Liang Hintan, Tumbang Topus, Sumber Barito, Kalimantan Tengah, Indonesia, coll. C. Rahmadi, 14 June 2004.

Diagnosis: Adult carapace transversely subquadrate, width to length ratio 1.23–1.25 (Figs. 6A, B, 7I); striae on lateral parts of carapace distinct (Figs. 6B, 7I); branchial regions gently convex in frontal view (Fig. 6C, E); dorsal margin of frontal median triangle contiguous with lateral margins (Fig. 6C–E); exorbital tooth with outer margin almost entire (Figs. 6B, 7I); epibranchial tooth very low to absent, if visible, separated from rest of margin by shallow low cleft, anterolateral margin may appear entire (Figs. 6B, 7I); median lobe of posterior margin of epistome acutely triangular (Fig. 6C–E); ischium of third maxilliped subquadrate (Fig. 7A); fingers of adult male cheliped closing along entire cutting margins (Fig. 7D); P3 and P4 dactyli subequal in length (Fig. 7F, G); male pleonal somite 6 subquadrate, slightly longer than broad (Fig. 7C); 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. 7B); adult Gl subterminal segment relatively stout; terminal segment subconical, distal half gently curved outwards, tapering gradually to subtruncate tip, 0.35 times length of subterminal segment, distal opening relatively smaller, subovate (Fig. 20Q–S); vulvae almost round (Fig. 23C).

Colour: Not known.

Remarks: Of the various characters Ng (2015) used to distinguish this species from B. tenebrosa and B. aspera, perhaps the most obvious is that the carapace of B. brachyphallus is much smoother, with the striae near the lateral regions relatively lower and more rounded (Figs. 6A, B, E, 7I). The short G1 terminal segment is a character now also shared with B. bario sp. nov., B. sarawakensis sp. nov. and B. serrata sp. nov., although the subterminal segment of B. brachyphallus is still proportionately the shortest and stoutest among congeners (Fig. 20Q–S).

Biology: Borneosa brachyphallus was collected from inside shallow streams in a horizontal cave in central Kalimantan, in the Barito Basin (Rahmadi and Suhardjono 2004), but it is clearly not a cavernicolous species as it has no the troglobitic adaptations (cf. Holthuis 1986; Guinot 1988 1994).