Platythelphusa

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.

==Taxonomic history== The first freshwater crab to be described from Lake Tanganyika, by Alphonse Milne-Edwards in 1887, was considered so distinct from the other crabs known up to that time that it was placed in a new genus, as Platythelphusa armata. Twelve years later, a second species was described by W. A. Cunnington, leader of the third Tanganyika Expedition, and was also placed in a separate genus, as Limnothelphusa maculata. The same author later described a third species, Platythelphusa conculata, and eventually realised that all three belonged to the same genus, reducing Limnothelphusa to a taxonomic synonym.