Demanietta sunthorni, a new species of freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from Adang-Rawi Island Group, Andaman Sea, south Thailand

A new species of a potamid crab belonging to the genus Demanietta Bott, 1966, is described from Adang Island, Andaman Sea, off Satun, south Thailand. Demanietta sunthorni, new species, belongs to a group of Demanietta species which has a distinct epibranchial tooth, and strong epigastric and postorbital cristae on the carapace. It can be distinguished from all congeners most easily by the form of the male first gonopod which is slender, with the terminal segment sinuous, upcurved and possessing a large dorsal fold. This is the southernmost record of the genus.