Establishment of A New Bornean Genus of Gecarcinucidae (Crustacea: Brachyura), with Descriptions of Five New Species.

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 and male first gonopod.