The freshwater gecarcinucid species from Borneo previously referred to Sundathelphusa Bott, 1969, are transferred to a new genus. Borneosa gen. nov. can be diagnosed by the presence of a distinct frontal median triangle that is shorter than the frontal margin, a relatively longer male thoracic sternum in which the sternopleonal cavity reaches more anteriorly, and a male first gonopod that has the terminal segment prominently covered with long setae. The eight species recognised—B. tenebrosa (Holthuis, 1979), B. aspera (Ng & Stuebing, 1989), B. brachyphallus (Ng, 2015), and five new species, B. niah, B. bario, B. kapit, B. sarawakensis and B. serrata—can be distinguished by characters of the frontal median triangle, epibranchial tooth, anterolateral margin, third maxillipeds, ambulatory legs, male sternum, male pleon andmale first gonopod.
Freshwater crab, Gecarcinucoidea, New species, New genus, Malaysia, Brunei, Indonesia, Taxonomy, Distribution, Key.
