; class Amphibia, order Urodela)
A family of what are probably neotenous (see neoteny), hynobiid descendants. Metamorphosis is incomplete, the gills are degenerate (hence the name, meaning ‘hidden gills’), the eyelids never develop, and larval teeth are retained throughout life. The head and body are broad and flattened, the tail laterally compressed, the skin smooth and slimy, and the habit totally aquatic. The largest extant amphibian, Andrias japonicus (Japanese giant salamander), is more than 1.5 m long and some are longlived (A. japonicus individuals are known to have lived for 50 years). Tertiary fossil species are distributed widely in the northern hemisphere, but there are only two living genera, comprising three species, in N. America and Asia.
Subjects: Zoology and Animal Sciences.