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Anura
Anura consists of 2,600 species of tail-less amphibians (as adults), such as toads and frogs. They characteristically have heads that merge directly into the trunk of the body. Toads have thicker skin than frogs and are more terrestrial. All amphibians in this order have external fertilization and lay eggs that develop into tailed tadpoles. They are distributed worldwide in temperate and tropical regions. Members of Anura primarily feed on insects and grow up to 12 inches in length.
Gymnophiona (Apoda)
Gymnophionans are limbless and have the appearance of large earthworms, growing as large as 60 inches in length. However, members of this order --- called caecilians --- have teeth, jaws and backbones that are characteristic of vertebrates. Caecilians are burrowing animals, generally exclusive to the subtropics and tropics, and are the only (living) amphibians that have scales. These scales have little to no function (vestigial) and are hidden between skin folds. Caecilians consist of 170 species with some remaining entirely aquatic. Terrestrial species feed on small invertebrates, including earthworms and termites, whereas aquatic species consume eels, fish and aquatic invertebrates.
Caudata (Urodela)
Caudata is comprised of 450 species of newts and salamanders, and is the only living order of tailed adult amphibians. Even though Caudatans usually grow within the range of 3-12 inches in length, giant salamanders can reach up to 59 inches. They primarily inhabit the northern temperate zone, with some species being distributed in South America and around the Equator. Lizard-like in appearance, members of this order feed on worms, insects and snails.
Commonalities
All amphibians are cold-blooded animals. Amphibians also have features similar to reptiles and fish. For example, as youth many amphibians have gills as do fish. Others have physical apparences that have reptilian attributes. Encompassing 3,500 species, amphibians --- whose name means "double life" --- are both terrestrial and aquatic. Vunerable to dehydration, they are primarily found close to swamps, ponds, marshlands and other freshwater sources. During unfavorable climatic conditions, such as dry and hot weather, many amphibians engage in self-induced periods of inactivity called estivation. Also, a number of amphibians camoflauge themselves by changing color so that they can blend in with their environment for protection.