The amphibia are distinguished by having usually no scales, by having eggs and embryos similar to those of fishes, and by undergoing a complete metamorphosis, the young having gills. There are three living orders: (1) The tailless, as the frogs (Anura); (2) The tailed (Urodela), as the salamanders, and the siren group (Sirenoidea), which retain the gills of the young state (hence called Perennibranchiata) through the adult state, among which are the siren, proteus, etc.; (3) The Coecilians, or serpentlike amphibia (Ophiomorpha or Gymnophiona), with minute scales and without limbs. The extinct Labyrinthodonts also belonged to this class. The term is sometimes loosely applied to both reptiles and amphibians collectively.