Platythelphusa is a genus of freshwater crabs endemic to Lake Tanganyika. It has been placed in a number of families, including a monotypic family, Platythelphusidae, as well as Potamidae and its current position in the Potamonautidae, and has also been treated as a subgenus of Potamonautes. It forms a monophyletic group, possibly nested within the genus Potamonautes, which would therefore be paraphyletic. The genus is the only evolutionary radiation of crabs to have occurred in a freshwater lake, and it occurred recently, probably since the Pliocene. This parallels the better known radiation of cichlid fishes in Lake Tanganyika. Only one other species of freshwater crab is found in Lake Tanganyika, Potamonautes platynotus.

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