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Pipids are highly aquatic frogs that rarely if ever venture out of water. They have several adaptations to aquatic life, including the loss of the tongue (tongues are not generally useful for feeding in water), and the presence of lateral line organs, which are used to detect wave motion in water (these are present in most groups of fishes). The group is sometimes called the Aglossa.
Pipid frogs are found in Africa, South America, and just get into Panama. Some species in South America, such as the Surinam Toad (Pipa pipa) are extremely flattened and look like roadkills. Females of the genus Pipa have an elaborate mating behavior, in which eggs are deposited on the back of the female, and the skin swells up around the eggs to encase them in pockets in which the embryos develop. In some species the eggs hatch out as tadpoles, but in others fully formed froglets emerge from the mother's back.
Tadpoles (when present) lack beaks and denticles, and have paired spiracles (if spiracles are present). This is the Orton type 1 tadpole, also found in Rhinophrynidae. There is much diversity in larval morphology and ecology in pipids. Tadpoles of Xenopus and Silurana are extremely efficient filter feeders. Tadpoles of Hymenochirus are carnivorous, eating larger prey items. In some species of Pipa the eggs (embedded in the mother's back) hatch out as tadpoles, but other species have direct development, in which froglets emerge.
The genus Xenopus (African Clawed frogs) has undergone drastic evolution in chromosome number, producing tetraploid (4n), and octoploid (8n), and even dodecaploid (12n) species. These higher levels of ploidy may have resulted from hybridization of between species. One species, Xenopus laevis, is widely used as a lab animal in molecular and developmental biology. The Dwarf Clawed Frogs (Hymenochirus) are very small, about 20-30 mm, and are widely sold in aquarium stores. The call of many pipid frogs is a clicking sound, which in Xenopus borealis is produced by forcefully pulling apart the large arytenoid cartilages of the larynx (voice-box), thus producing a "pop" by implosion.