Borneosa niah, 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 : 12

Borneosa niah sp. nov.

( Figs. 8 , 9 , 21A–D ) urn:lsid:zoobank.org:act:5EB6A04C-E114-4F4E-ACA4-C9D76BC5F8A4

Material examined: 1 male (22.6 × 19.1 mm) (ZRC 2006.064), Bukit Kasut, in river along trail to jetty, in isolated hill some distance from Niah massif, Niah, ca. 3.80°N 113.77'E, Sarawak, Malaysia, coll. I. Das, November 2002.

Diagnosis: Adult carapace transversely subquadrate, width to length ratio 1.18 ( Fig. 8A, B ); striae on lateral parts of carapace distinct ( Fig. 8B ); branchial regions gently convex in frontal view ( Fig. 8C, F ); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 8C–E ); exorbital tooth with outer margin almost entire ( Fig. 8B ); epibranchial tooth distinct, separated from rest of margin by low cleft ( Fig. 8B ); median lobe of posterior margin of epistome obtusely triangular ( Fig. 8C–E ); ischium of third maxilliped subquadrate ( Fig. 9A ); fingers of adult male cheliped closing along entire cutting margins ( Fig. 9D, E ); P3 and P4 dactyli subequal in length ( Fig. 9G, H ); male pleonal somite 6 subquadrate, slightly longer than broad ( Fig. 9C ); 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. 9B ); adult Gl subterminal segment relatively slender; terminal segment subcylindrical, distal half gently curved outwards, tapering gradually to truncate tip, 0.30 times length of subterminal segment, distal opening large, subovate ( Fig. 21A–C ); females not known.

Colour: Not known.

Etymology: The species is named after its type locality in Niah. The name is used as a noun in apposition.

Remarks: Borneosa niah sp. nov. has a G1 that is similar to that of B. tenebrosa although the terminal segment is relatively longer ( Fig. 21B, C ) when compared to specimens of B. tenebrosa of similar sizes ( Fig. 20F, G ). In addition, the frontal median triangle of B. niah is complete, with the dorsal margin confluent with the lateral margins ( Fig. 8C–E ) (versus dorsal margin of frontal median triangle separated from lateral margins by a small gap or connected by small granules in B. tenebrosa ; Fig. 2C–E ); and the epibranchial tooth is relatively well-developed and strong ( Fig. 8B ) (versus low to almost confluent with anterolateral margin in B. tenebrosa ; Figs. 2B , 3E ). The two species are adjacent to each other in their distribution, with that of B. niah in Niah only just west of the Mulu area where B. tenebrosa occurs. Both highlands, however, are separated by lowland rainforests and their drainages are not connected.

Biology: The only known specimen was collected from a stream with rocky substrates in the Niah limestone hills but not from a cave (I. Das, pers. comm.).

Figures

Fig. 8. Borneosa niah sp. nov., holotype male (22.6 × 19.1 mm) (ZRC 2006.064), Niah, 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. 9. Borneosa niah sp. nov., holotype male (22.6 × 19.1 mm) (ZRC 2006.064), Niah, Sarawak. A, left third maxilliped; B, anterior male thoracic sternum and pleon; C, male pleon; D, outer view of right chela; E, outer view of left chela; F–I, left P2–P5, respectively, all to same scale.

Fig. 21. A–D, Borneosa niah sp. nov., holotype male (22.6 × 19.1 mm) (ZRC 2006.064), Niah, Sarawak; E–G, B. bario sp. nov., holotype male (29.6 × 23.1 mm) (ZRC 2021.0692), Bario, Sarawak. Scale bars:A, D, E, H = 1.0 mm; B, C, F, G = 0.5 mm.

Fig. 20. A–E, Borneosa tenebrosa (Holthuis, 1979), male (16.1 × 13.0 mm) (ZRC 2013.1293), Gunong Mulu National Park, Sarawak; F–H, B. tenebrosa (Holthuis, 1979), paratype male (21.9 × 17.8 mm) (NHM 1979.136), Gunong Mulu National Park, Sarawak; I–L, B. tenebrosa (Holthuis, 1979), holotype male (23.5 × 19.1 mm) (NHM 1979.135), Gunong Mulu National Park, Sarawak (structures laterally inverted for comparative purposes); M–P, B. aspera (Ng & Stuebing, 1989), male (32.3 × 25.4 mm) (ZRC 2014.845), Temburong, Brunei; Q–T, B. brachyphallus (Ng, 2015), holotype male (27.1 × 22.0 mm) (MZB Cru 4396), Sungei Barito, central Kalimantan. Scale bars: A, D, E, F, G, J, K, N, O, R, S = 0.5 mm; B, C = 0.1 mm; H, I, L, M, P, Q, T = 1.0 mm

Fig. 2. Borneosa tenebrosa (Holthuis, 1979), holotype male (23.5 × 19.1 mm) (NHM 1979.135), Gunong Mulu National Park, 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. 3. Borneosa tenebrosa (Holthuis, 1979). A–D, holotype male (23.5 × 19.1 mm) (NHM 1979.135), Gunong Mulu National Park, Sarawak; E, paratype male (21.9 × 17.8 mm) (NHM 1979.136), Gunong Mulu National Park, Sarawak; F–I, female (30.8 × 24.6 mm) (ZRC 1989.3420), Gunong Mulu National Park, Sarawak. A, left third maxilliped; B, anterior male thoracic sternum and pleon; C, male pleon; D, outer view of right chela; E, dorsal view of carapace; F–I, left P2–P5, respectively, all to same scale.