Most amphibians maintain close ties with water and are most abundant in damp habitats such as swamps and rain forests. Most amphibians rely heavily on their moist skin to carry out gas exchange with the environment. Some terrestrial species lack lungs and breathe exclusively through their skin or oral cavity. Amphibian eggs lack a shell and dehydrate quickly in dry air. Amphibians generally lay their eggs in ponds or swamps or at least in moist environments.
Some urodeles are entirely aquatic, but others live on land as adults or throughout life.
Anurans are more specialized than urodeles for moving on land. Adult frogs use their powerful hind legs to hop. The apodans are legless and nearly blind and resemble earthworms. Class Reptilia Reptiles have several adaptations for terrestrial living not generally found in amphibians. Scales containing the protein keratin waterproof the skin of a reptile, helping prevent dehydration in dry air.