A new genus for cave-dwelling crabs previously assigned to Sesarmoides (Crustacea : Decapoda : Brachyura : Sesarmidae)

The semi-terrestrial crab genus Sesarmoides is restricted to three species of Indo-West Pacific intertidal mangrove and estuarine crabs, S. kraussi, S. longipes and S. borneensis. Twelve other species previously placed in Sesarmoides are here transferred to a new genus, Karstarma. The species of Sesarmoides are distinguished from those of Karstama by the presence of a stridulatory structure consisting of a longitudinal crest on the cheliped merus that is used to rub against a ridge of suborbital granules. This form of stridulation is apparently unique within the Sesarmidae, although common in the Varunidae. Other features distinguishing species of Sesarmoides sensu stricto from those of Karstama are their relatively smaller adult carapace size, a relatively shallower median epigastric groove, the presence of a longitudinal row of small granules or ridge on the outer surface of the cheliped pollex, and a relatively more slender male first gonopod.