The term "amphibian" comes from Greek amphi, both, and bios, life, reveals the main characteristic of this class of animals that live in water or on land according to the stage of development where they are located. As a result, have different ways of breathing. In the larval stage living in water and breathe through gills similar to those with fish, in adulthood, and on earth, they do through their lungs, underdeveloped. Some species, such as salamanders, which have no gills or lungs, breathe through the lining of the mouth and larynx, and also through the skin, but all amphibians swallowed air, for they have no diaphragm. Another important feature of this class of animals is that they have a simple skeleton with skull and many small cartilaginous areas, which provide them with great elasticity. Amphibians include the order of the names (without feet), as tapalcuax; that of urodeles (with visible tail) as the salamander, the axolotl and newt, and the Anura (tailless), as frogs, toads and frogs.
The number of members with amphibians varies by gender: frogs, toads and salamanders have four legs, the great horn and other urodeles, 2 members, and the nicknames, none.
Amphibians have a body temperature that varies with the environment, because their circulatory system is incomplete and the blood is well oxygenated.
Most amphibians move from aquatic to terrestrial life after experiencing a process of morphological and physiological changes known COPM metamorphosis.