Gymnophiona, also called Apoda, one of the three major extant orders of the class Amphibia. Its members are known as caecilians, a name derived from the Latin word caecus, meaning “sightless” or “blind.” The majority of this group of limbless, wormlike amphibians live underground in humid tropical regions throughout the world. Because of their relatively hidden existence, caecilians are unfamiliar to the layperson and are not usually considered in discussions about amphibians.
. They are nevertheless a fascinating group of highly specialized amphibians about which there is still much to be learned.
Several species of caecilians in the South American genus Caecilia exceed 1 metre (about 3.3 feet) in total length; the largest known caecilian is C. thompsoni, at 152 cm (about 60 inches). The smallest caecilians are Idiocranium russeli in West Africa and Grandisonia brevis in the Seychelles; these species attain lengths of only 98–104 mm (3.9–4.1 inches) and 112 mm (4.4 inches), respectively.