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Any of several tropical freshwater fish of the order or subclass Dipnoi that, in addition to having gills, have lunglike organs for breathing air. Lungfish have a long, narrow body, and certain species can survive periods of drought inside a mucus-lined cocoon in the mud. The lungfish and the coelacanths are the only living lobe-finned fishes.
any of six species (three species according to some authorities) of air-breathing fishes placed with a number of extinct forms in the subclass Dipnoi (order Dipnoi of some authorities). The Dipnoi first appeared in the Lower Devonian Period (about 370,000,000-395,000,000 years ago). The extant species occur in rivers and lakes in Africa, South America, and Australia. They are especially interesting because of their characteristic body forms, their generally large size, their erratic distribution over the tropical regions of the earth, and their peculiar mode of life.