These frogs are exclusively aquatic and have numerous morphological modifications befitting their habitat. For example, the feet are completely webbed, the body is flattened, and a lateral line system is present. In addition, pipids possess highly modified ears for producing and receiving sound underwater. They lack a tongue or vocal cords, instead having bony rods in the larynx that help produce sound. They range from 4 to 19 cm (1.6 to 7.5 in) in body length.
The fossil record for pipids is relatively good, with 12 extinct species known. Six of these are placed in the extant genus Xenopus, the remainder in extinct genera. These fossils are known from Africa, South America, and the Middle East back to the Lower Cretaceous.
Hymenochirus (4 species) (dwarf clawed frogs) Pipa (7 species) (Surinam toads) Pseudhymenochirus (Monotypic) Silurana (2 species) (tropical clawed frogs) Xenopus (21 species) (common clawed frogs)