Establishment of A New Bornean Genus of Gecarcinucidae (Crustacea: Brachyura), with Descriptions of Five New Species. Author Ng, Peter K L Author Grinang, Jongkar text Zoological studies 2022 2022-05-05 61 13 1 35 http://dx.doi.org/10.6620/ZS.2022.61-13 journal article 54577 10.6620/ZS.2022.61-13 854b8390-f85f-4b0a-8c7a-2bfc1da39225 PMC9579960 36330021 8074520 Borneosa serrata sp. nov. ( Figs. 17 , 18 , 22M–P ) 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 . Diagnosis : Adult carapace transversely subquadrate, width to length ratio 1.16 ( Fig. 17A, B ); striae on lateral parts of carapace distinct ( Fig. 17B ); branchial regions gently convex in frontal view ( Fig. 17C, F ); dorsal margin of frontal median triangle contiguous with lateral margins ( Fig. 17C–E ); exorbital tooth with outer margin serrated ( Fig. 17B ); epibranchial tooth prominent, separated from rest of margin by distinct cleft ( Fig. 17B ); median lobe of posterior margin of epistome acutely triangular ( Fig. 17C–E ); ischium of third maxilliped subrectangular ( Fig. 18A ); fingers of adult male cheliped closing along entire cutting margins ( Fig. 18E ); P3 and P4 dactyli subequal in length ( Fig. 18G, H ); male pleonal somite 6 subquadrate, slightly longer than broad ( Fig. 18C ); 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 ); 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 ); 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 ) (versus almost smooth in B. niah ; Fig. 8B ); the median tooth on the posterior margin of the epistome is sharply triangular in shape ( Fig. 17C– E ) (versus blunter in B. niah ; Fig. 8C–E ); the third maxilliped ischium is proportionately longer ( Fig. 18A ) (versus proportionately shorter in B. niah ; Fig. 9A ); the male pleon (notably somites 3–5) is relatively more narrow ( Fig. 18C ) (versus relatively wider in B. niah ; Fig. 9C ); and the G1 terminal segment is relatively longer ( Fig. 22M–O ) (versus relatively shorter in B. niah ; Fig. 21A–C ). 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 ) (versus tooth very low to almost absent in B. brachyphallus with the anterolateral margin appearing almost entire; Figs. 6B , 7I ); the outer margin of the exorbital tooth is tuberculate and appears serrated ( Fig. 17B ) (versus almost smooth in B. brachyphallus ; Figs. 6B , 7I ); the third maxilliped ischium is proportionately longer ( Fig. 18A ) (versus shorter in B. brachyphallus ; Fig. 7A ); 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 ) (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 ); male pleonal somite 6 is distinctly longer ( Fig. 18C ) (versus proportionately shorter and more quadrate in B. brachyphallus ; Fig. 7C ); and the G1 subterminal segment is slightly longer ( Fig. 22M–O ) (versus relatively shorter in B. brachyphallus ; Fig. 20Q–S ). © 2022 Academia Sinica, Taiwan 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.).