Borneosa serrata, 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 : 23-24

publication ID	https://doi.org/ 10.6620/ZS.2022.61-13
DOI	https://doi.org/10.5281/zenodo.8055978
persistent identifier	https://treatment.plazi.org/id/CF2E433D-3C24-FFB4-FE98-FB0334F8FEB9
treatment provided by	Valdenar
scientific name	Borneosa serrata
status	sp. nov.

Treatment

Borneosa serrata View in CoL sp. nov.

( Figs. 17 View Fig , 18 View Fig , 22M–P View Fig ) urn:lsid:zoobank.org:act:B65416DA-4501-43C1-A0FB-31C9D46816A0

Material examined: 1 male (25.5 × 22.0 mm) (ZRC 2006.57), Sungei Pangean (= Pengean), Long Yiu Hulu, Kabupaten Bulungan, Kalimantan Utara, ca. 2.7°N 116.7°E, Indonesia, coll. R. Diesel, 20 August 1995. GoogleMaps

Diagnosis: Adult carapace transversely subquadrate, width to length ratio 1.16 ( Fig. 17A, B View Fig ); striae on lateral parts of carapace distinct ( Fig. 17B View Fig ); branchial regions gently convex in frontal view ( Fig. 17C, F View Fig ); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 17C–E View Fig ); exorbital tooth with outer margin serrated ( Fig. 17B View Fig ); epibranchial tooth prominent, separated from rest of margin by distinct cleft ( Fig. 17B View Fig ); median lobe of posterior margin of epistome acutely triangular ( Fig. 17C–E View Fig ); ischium of third maxilliped subrectangular ( Fig. 18A View Fig ); fingers of adult male cheliped closing along entire cutting margins ( Fig. 18E View Fig ); P3 and P4 dactyli subequal in length ( Fig. 18G, H View Fig ); male pleonal somite 6 subquadrate, slightly longer than broad ( Fig. 18C 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. 18B View Fig ); adult Gl subterminal segment relatively slender; terminal segment subconical, distal half gently curved outwards, tapering gradually to subtruncate tip, 0.31 times length of subterminal segment, distal opening large, ovate ( Fig. 22M–O View Fig ); females not known.

Colour: When freshly collected, the specimen was a uniform dark brown on all the dorsal surfaces (R. Diesel, pers. comm.).

Etymology: The species is named for the serrated appearance of the anterolateral margin, with the epibranchial tooth prominent.

Remarks: Morphologically, B. serrata sp. nov. most closely resembles B. niah sp. nov., especially in the presence of a more well-developed epibranchial tooth separated from the anterolateral margin by a deep cleft; and the male sternopleonal cavity projects deeper into thoracic sternite 3 with only a narrow space present between the tip of the cavity and the suture between sternites 1 and 3. Borneosa serrata , however, can be distinguished in having the outer margin of the exorbital tooth serrated ( Fig. 17A View Fig ) (versus almost smooth in B. niah ; Fig. 8B View Fig ); the median tooth on the posterior margin of the epistome is sharply triangular in shape ( Fig. 17C– E View Fig ) (versus blunter in B. niah ; Fig. 8C–E View Fig ); the third maxilliped ischium is proportionately longer ( Fig. 18A View Fig ) (versus proportionately shorter in B. niah ; Fig. 9A View Fig ); the male pleon (notably somites 3–5) is relatively more narrow ( Fig. 18C View Fig ) (versus relatively wider in B. niah ; Fig. 9C View Fig ); and the G1 terminal segment is relatively longer ( Fig. 22M–O View Fig ) (versus relatively shorter in B. niah ; Fig. 21A–C View Fig ).

The G1 structure of B. serrata is very close to that of B. brachyphallus , but B. serrata can be separated in possessing a distinct epibranchial tooth ( Fig. 17B View Fig ) (versus tooth very low to almost absent in B. brachyphallus with the anterolateral margin appearing almost entire; Figs. 6B View Fig , 7I View Fig ); the outer margin of the exorbital tooth is tuberculate and appears serrated ( Fig. 17B View Fig ) (versus almost smooth in B. brachyphallus ; Figs. 6B View Fig , 7I View Fig ); the third maxilliped ischium is proportionately longer ( Fig. 18A View Fig ) (versus shorter in B. brachyphallus ; Fig. 7A View Fig ); the male sternopleonal cavity projects deeper into thoracic sternite 3, with only a narrow space present between the cavity and the suture between sternites 1 and 3 ( Fig. 18B View Fig ) (versus there is a wider gap between the tip of the male sternopleonal cavity and the suture between sternites 2 and 3 in B. brachyphallus ; Fig. 7B View Fig ); male pleonal somite 6 is distinctly longer ( Fig. 18C View Fig ) (versus proportionately shorter and more quadrate in B. brachyphallus ; Fig. 7C View Fig ); and the G1 subterminal segment is slightly longer ( Fig. 22M–O View Fig ) (versus relatively shorter in B. brachyphallus ; Fig. 20Q–S View Fig ).

Biology: The specimen was collected in a small tributary with rock substrates and dense forest cover in the centre of Kalimantan Utara (R. Diesel, pers. comm.).