animal with both lungs and gills
• (n.) One of a tribe of Amphibia, which have both lungs and gills at the same time, as the proteus and siren.
Am·phip'neust noun [ Greek ... + ... one who breathes, ... to breathe.] (Zoology) One of a tribe of Amphibia, which have both lungs and gills at the same time, as the proteus and siren. 
amphipneust An animal that breathes both by lungs and by gills; a name given by some to the lowest order of the Amphibious animals, including the Proteus and Siren, which retain their gills all their lives.