The word amphibian comes from the Greek word for “double-life,” referring to the fact that amphibians start life in water breathing through gills before maturing into lung-breathing land animals, although most never stray too far from water. The class Amphibia is composed of only 3 orders. The order Anura, a word that refers to tailless amphibians, includes frogs and toads ( see Table: Similarities and Differences Between Frogs and Toads Similarities and Differences Between Frogs and Toads ). This is the largest order, with more than 3,500 species. The order Caudata, or amphibians with tails—salamanders, newts, and sirens—has about 375 species ( see Table: Some Common Salamanders and Newts Some Common Salamanders and Newts ). The Gymnophiona order is made up of caecilians: legless, tailless amphibians that spend most of their time burrowing. It has about 160 species.