Isolapotamon spp.

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 : 125-126

Isolapotamon spp.

( Fig. 7A, B )

Material examined. 1 juvenile female 7.8 × 8.9 mm, Lubang Tebot Cave, Merabu karst, East Kalimantan, Borneo , 1°34’58”N, 117°21’07”E, 360 m, 09 August 2010, MZB Cru 5711 .

Remarks. In the Lubang Tebot Cave, Kalimantan (East Kalimantan), Borneo, located a little further south on the karst of Merabu than Lubang Gedung ( Fig. 1B ), two species were collected: one is a potamid, the other is a gecarcinucid (see below, under gecarcinucid sp.). The potamid, an early juvenile female ( Fig. 7B ), is short-legged: it belongs to the genus Isolapotamon ( Bott 1968; Ng 1987; Ng & Tan 1998; Grinang et al. 2018). Its small size does not allow a specific identification (P.K.L. Ng, pers. comm.).

The Lubang Bayan Cave, located very close to the village of Merapun, Borneo ( Fig. 1B ), 01°28’56”N, 117°11’32”E, is home to a rich and varied fauna, including a species of crab. This crab ( Fig. 7A ) was photographed in situ in the river eating a fish (possibly a cyprinid; P.K.L. Ng, pers. comm.), but was not collected. It is an unmodified species of Isolapotamon and likely a trogloxene (see Fig. 7A showing the eyes with pigmented cornea and relatively stout ambulatory legs). This report on predation of an entire and rather large riverine fish by the potamid is interesting. Cave environments have been assumed to be predator-free sanctuaries for cave fishes by Romero & Green (2005), but the study of Klaus & Plath (2011) on the freshwater crab Avotrichodactylus bidens (Bott, 1969) in a sulfidic southern Mexican cave shows that it preys on cave-dwelling fish and thus may be one of the top predators in this subterranean habitat. The case here is very different since both crab and fish are trogloxenes. Freshwater epigean crab predation on fish is known from ancient times to the present day but it is focused on Potamon species, so our knowledge on the diet of other freshwater cave crabs is still poor.

Figures

FIGURE 1. A, Borneo Island and Kalimantan; B, Karst of Merabu, East Kalimantan, northernmost limestone massif of the Mangkalihat Peninsula; C, D, Lubang Gedung Cave, two views. Courtesy, J. and B. Lips.

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.