Xenopus

Xenopus commonly known as the clawed frog) is a genus of aquatic frogs native to sub-Saharan Africa. 
Twenty species are known. The two best-known species of this genus are "Xenopus laevis" and "Xenopus tropicalis", which are studied as model organisms for developmental biology, cell biology, toxicology, neuroscience and for modelling human disease and birth defects.
The genus is also known for its polyploidy, with some species having up to 12 sets of chromosomes. The frogs are all excellent swimmers and have powerful, fully webbed toes, though the fingers lack webbing. Three of the toes on each foot have conspicuous black claws.