The thirty species in the family Pipidae are found in tropical
South America (Pipa) and sub-Saharan Africa (four other genera).
These frogs are exclusively aquatic and have numerous
morphological modifications befitting their habitat. For
example, the feet are completely webbed and a lateral line
system is present. In addition, pipids possess highly modified
ears and vocal structures for producing and receiving sound
underwater. Pipids are also unique among known frogs in not
having a tongue and possessing "claws" on one or more toes (not
present in Pipa). Pipids are relatively primitive frogs, most
closely related to the Rhinophrynidae. Some primitive
characteristics of pipids include inguinal amplexus and
opisthocoelous vertebrae, however, many aspects of pipid
morphology are seemingly derived for an aquatic lifestyle. Some
species of pipids have an elaborate courtship ritual that
involves a variety of underwater acrobatics. In Pipa, the sticky
eggs are taken by the male after deposition and pressed into th