Gecarcinucidae Rathbun, 1904

Guinot, Danièle & Rodríguez Moreno, Paula A., 2024, Ngan mayla gen. et sp. nov, a new blind potamid cave crab from Borneo, Kalimantan (Crustacea: Decapoda: Brachyura: Potamoidea, Potamidae), and three other unidentified cave crabs from the same region, Zootaxa 5476 (1), pp. 115-137 : 126

Family Gecarcinucidae Rathbun, 1904

Gecarcinucid sp.

( Fig. 8 )

Material examined. 1 juvenile female 7.7 × 9.9 mm, Lubang Tebot Cave, Merabu karst, East Kalimantan, Borneo , 1°34’58”N, 117°21’07”E, 360 m, 09 August 2010, MZB Cru 5712 .

Remarks. Different from the Isolapotamon sp. mentioned before ( Fig. 7A, B ), the present specimen is a gecarcinucid as shown by the bilobed last article of the mandibular palp. It is depigmented (only brownish pale coloured body; white pereiopods); the eyes barely fill one-third of the orbit and tend to be ogive-shaped; the cornea is black-pigmented ( Fig. 8B ).

A short diagnosis of the juvenile female follows: carapace dorsal surface gently convex ( Fig. 8A ); anterolateral margin distinctly convex, with marked indentation, lined with small rounded granules; areas adjacent to antero- and posterolateral margins covered with numerous distinct oblique striae, anteriorly mixed with very short setae; rugose epigastric cristae on two prominences ( Fig. 8A, B ); postorbital cristae well discernible; frontal margin not gradually confluent with supraorbital margin, conversely the both being almost at right angle; a frontal triangle not developed and, instead, a narrow proepistome; posterior margin of epistome undulated; chelipeds ( Fig. 8C ) elongate; chela slender, outer surface covered with small sharp granules; fingers slightly longer than palm, curved distally to corneous tip; ambulatory legs very long and thin, second pair longest ( Fig. 8A, D ); outer surface rugose; dorsal, ventral margins of meri subcristate, gently serrated; propodus with small sharp granules on margins; dactylus very long, slightly downcurved, with numerous strong, anteriorly directed spines on dorsal, ventral margins, and corneous tip.

This gecarcinucid sp. from Lubang Tebot Cave in the Merabu Karst is reminiscent of Balssiathelphusa Bott, 1969 , of which Ng & Guinot (2014) described a cavernicolous species, B. phasma , collected in 2002 ( Degouve et al. 2002) in the main gallery of Gua Kambing situated in the same region of East Kalimantan, and represented by a male, the holotype 23.1 × 18.9 mm (MNHN-IU-2013-13148) and a female, paratype (ZRC 2014.0092) ( Ng & Guinot 2014: figs. 1–3). Both species have eyes with dark pigment and similar pale colouration of the carapace and legs, but gecarcinucid sp. differs from the typical B. phasma in having cylindrical eyestalks tending to an ogival shape and much more longer and thinner ambulatory legs. It could be considered a troglobite, more than a troglophile. According to P.K.L. Ng (pers. comm.), it could actually belong to a new genus but the fact that it is a young female does not allow recourse to the male characters, which are mainly decisive for making a taxonomic decision. This question will be discussed in a forthcoming article dealing with a species of Balssiathelphusa , namely two females, collected in 2007 (‘Borneo 2007’) in the Kecabe Cave located in the same karst as the type series, the Sungai Baai ( Lips et al. 2007: 27, 2 figs). Although these two caves are not considered to be part of the same river system (the Gua Kambing river system for the B. phasma type series, see Degouve et al. 2002: 2, map; and the Sungai Baai river system for the crab from Kecabe cave, see Lips et al. 2007), these two specimens are identified as B. phasma .

Figures

FIGURE 7. A, Isolapotamon sp., Lubang Bayan Cave, Merabu Karst, East Kalimantan, Borneo, 01°28’56”N, 117°11’32”E, August 2010, photographed in situ in the river preying on barb; crab not collected, probably a trogloxene; B, Isolapotamon sp., juvenile female, 7.8 × 8.9 mm, Lubang Tebot Cave, Kalimantan (East Kalimantan), Borneo, 1°34’58”N, 117°21’07”E, 360 m, 09 August 2010, MZB Cru 5711. Scale bar: B = 5 mm.

FIGURE 8. Gecarcinucid sp., juvenile female, 7.7 × 9.9 mm, Lubang Tebot Cave, Merabu Karst, East Kalimantan, Borneo, 1°34’58”N, 117°21’07”E, 360 m, 09 August 2010, MZB Cru 5712:A, habitus; B, frontal view; C, cheliped; D, ventral view; E, thoracic sternum. Scale bars: A, B, D, E = 5 mm; C = 1 mm.