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lungfish, common name for any of a group of fish belonging to the families Ceratodontidae and Lepidosirenidae, found in the rivers of South America, Africa, and Australia. Like the lobefins, the lungfishes are ancestrally related to the four-footed land animals. Fossil lungfish have been found in the United States, Europe, and India. Of the living specimens, the most primitive is an Australian species, a stout-bodied 5-ft (150-cm) fish with paired fins set on short stumps. The function of its lungs is not clearly understood. The fins of other lungfishes have become long, wispy sense organs. They are in general more eellike in appearance. Best-known are the African species, which hibernate in hard clay balls during the dry season. They line their retreat with a waterproof membrane of dried mucus and apply their mouths to tubes of this material that serve as airshafts from the cocoons to the surface of the ground. They can remain dormant in this manner for up to three years. In water, the African lungfishes breathe with gills. The South American loalach is totally dependent on air and will drown if held underwater. Its eggs are laid in a long tunnel at the bottom of a swamp and are guarded by the male, which sprouts red filamental gills from his pelvic fins. The young are also equipped with temporary external gills. Lungfish feed on snails and plants, storing quantities of fat for sustenance during hibernation. Lungfish are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Dipteriformes, families Ceratodontidae and Lepidosirenidae.
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