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

We here report on freshwater cave crabs of the families Potamidae and Gecarcinucidae in East Kalimantan, Sarawak, Indonesia in Borneo. A new genus and species of potamid crab, Ngan mayla, is described from Lubang Gedung Cave in the Merabu Karst. With its bullet-shaped eyes, Ngan mayla gen. et sp. nov. is totally blind and also displays the characters associated with an obligate cave-dwelling life, namely that it is dolichopod and fully depigmented. The closest genus and species is Cerberusa caeca Holthuis, 1979, from northern Sarawak. Highly modified, Ngan mayla gen. et sp. nov. proves to be among the most troglobitic of the known subterranean potamids, of which there were currently only seven in the Old World, with only four simultaneously being completely blind, entirely depigmented and dolichopod (Cerberusa caeca Holthuis, 1979, Diyutamon cereum Huang, Shih & Ng, 2017 and Phasmon typhlops Huang, Ahyong & Shih, 2020, to which must be added today Ngan mayla gen. et sp. nov.). Ngan mayla gen. et sp. nov. is easily distinguished from other potamid genera by its chelipeds bearing numerous acute teeth, spines (some horn-tipped) and short simple setae or spine-like setae on all articles. Two young female crabs collected in 2010 at the same area (Merabu Karst) but from a different cave, the Lubang Tebot Cave, could not be identified to specific level: an Isolapotamon sp., and a gecarcinucid with very long legs, pale colouration and slightly modified but black-pigmented eyes, close to Balssiathelphusa Bott, 1969, could possibly belong to a new genus. Some information on New World troglobitic crabs is provided.