A member of the subclass Dipnoi of the Osteichthyes
that contains a large number of fossil forms and three living freshwater
groups, found in Africa, South America, and Australia respectively. As their
names suggests, the lungfish have lungs, organs
not fund in any other living fish. The African and South American lungfish
are unusual in their ability to aestivate (see aestivation)
in cocoons of mud during droughts.