The freshwater crabs of Macau, with the description of a new species of Nanhaipotamon Bott, 1968 and the redescription of Nanhaipotamonwupingense Cheng, Yang, Zhong & Li, 2003 (Crustacea, Decapoda, Potamidae).

Four species of freshwater crabs from three genera and two families (Cantopotamon hengqinense Huang, Ahyong & Shih, 2017, Nanhaipotamon guangdongense Dai, 1997, Nanhaipotamon macau sp. n., and Somanniathelphusa zanklon Ng & Dudgeon, 1992) are documented from Macau for the first time. One new species, Nanhaipotamon macau sp. n., is described. The large flap on the male first gonopod terminal segment sets it apart from all other known congeners except N. wupingense Cheng, Yang, Zhong & Li, 2003, from Fujian. Characters of the carapace, male first gonopod and size, however, clearly differentiate these two species. Preliminary genetic studies also suggest that the two are not closely related. A neotype is designated for N. wupingense. The taxonomic status of Nanhaipotamon guangdongense is also discussed. Notes on the general biology and conservation status of these crabs are also included.