Borneosa bario, 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 : 12-17

publication ID	https://doi.org/ 10.6620/ZS.2022.61-13
DOI	https://doi.org/10.5281/zenodo.8055968
persistent identifier	https://treatment.plazi.org/id/CF2E433D-3C39-FFB3-FC62-FDA33652FBF9
treatment provided by	Valdenar
scientific name	Borneosa bario
status	sp. nov.

Treatment

Borneosa bario View in CoL sp. nov.

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

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

Material examined: Holotype: male (29.6 × 23.1 mm) ( ZRC 2021.0692 View Materials ), 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 GoogleMaps . 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 View Fig , 11F, H View Fig ); striae on lateral parts of carapace distinct ( Figs. 10B View Fig , 11F, H View Fig ); branchial regions gently convex in frontal view ( Fig. 10C View Fig ); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 10C–F View Fig ); exorbital tooth with outer margin almost entire ( Figs. 10B View Fig , 11F, H View Fig ); epibranchial tooth distinct, separated from rest of margin by distinct U-shaped cleft ( Figs. 10B View Fig , 11F, H View Fig ); median lobe of posterior margin of epistome obtusely triangular ( Fig. 10C–E View Fig ); ischium of third maxilliped subrectangular ( Fig. 11A View Fig ); fingers of adult male cheliped closing along entire cutting margins or with small basal gape ( Figs. 11D, E, G View Fig ); P3 and P4 dactyli subequal in length ( Fig. 11J, K View Fig ); male pleonal somite 6 subquadrate, longer than broad ( Fig. 11C View Fig ); 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 View Fig ); 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 View Fig ); vulvae transversely subovate ( Fig. 23D View Fig ).

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 View Fig ).

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 View Fig , 11F, H View Fig ) (versus tooth very low to obscure, and separated by a shallow narrow cleft at most in B. tenebrosa ; Fig. 2B View Fig ); the dorsal margin of frontal median triangle is contiguous with lateral margins ( Fig. 10C–F View Fig ) (versus separated by a gap or connected by small flattened granules in B. tenebrosa ; Fig. 2C– F View Fig ); the P3 and P4 dactyli subequal in length ( Fig. 11J, K View Fig ) (versus P3 dactylus longer than P4 dactylus in in B. tenebrosa ; Fig. 2G, H View Fig ); and the G1 terminal segment is proportionately stouter and shorter ( Fig. 21E–G View Fig ) (versus more elongate and slender in adult B. tenebrosa ; Fig. 20I–K View Fig ).

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 View Fig , 11F, H View Fig ) (versus tooth smaller and cleft shallow in B. niah ; Fig. 8B View Fig ); the third maxilliped ischium being proportionately longer ( Fig. 11A View Fig ) (versus distinctly shorter in B. niah ; Fig. 9A View Fig ); and the G1 terminal segment is proportionately stouter and shorter in adult males ( Fig. 21E–G View Fig ) (versus terminal segment more slender and longer in B. niah ; Fig. 21A–C View Fig ). From B. serrata , B. bario can be distinguished in having the outer margin of the exorbital tooth entire ( Fig. 10B View Fig ) (versus gently serrated in B. serrata ; Fig. 17B View Fig ); the ischium of the third maxilliped is proportionately longer ( Fig. 11A View Fig ) (versus clearly shorter in B. serrata ; Fig. 18A View Fig ); and the G1 subterminal segment is relatively stouter ( Fig. 21E–G View Fig ) (versus slenderer in B. serrata ; Fig. 22M–O View Fig ).

The fingers of the major chela of the holotype male do not obviously gape when closed ( Fig. 11D View Fig ) but that of a slightly larger paratype male shows a distinct small gape ( Fig. 11G View Fig ). 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.