Lungfish

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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lungfish

any freshwater bony fish of the subclass Dipnoi, having an air-breathing lung, fleshy paired fins, and an elongated body. The only living species are those of the genera Lepidosiren of South America, Protopterus of Africa, and Neoceratodus of Australia

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lungfish [′ləŋ‚fish]

(vertebrate zoology)

The common name for members of the Dipnoi; all have lungs that arise from a ventral connection with the gut.

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Lungfish 

(Dipnoi). a subclass of fishes in which, along with gill respiration, there is also pulmonary respiration. Lungfish have a peculiar “lung” attached to the esophagus instead of a sound. The body is elongated, in some compressed from the sides and in others eel-like. The upper jaw is grown together with the skull (autostylism), the notochord is preserved throughout life, and the unpaired fins have a peculiar feathery structure. The paired extremities have an axial jointed ray, with separate rays branching off from it in two directions (biserial archipterygial type). There are internal nares, or choanae. The heart has an arterial cone and its auricle is partly divided into a right and a left side. There is pulmonary blood circulation. The intestine has a spiral valve and opens into the cloaca.

There are 12 families of Dipnoi, nine of them fossil and three extant: (1) Ceratodontidae, which comprises one genus with one species, Australian lungfish, (2) Lepidosirenidae, comprising one genus with one species, Lepidosiren paradoxa (South American), and (3) Protopteridae, which includes one genus with three species all known as the African lungfish (from central Africa). Lungfish are freshwater fishes; they live in slow-running and drying bodies of water. Their length reaches 2 m. They feed on invertebrates, fishes, and amphibians. Some (Australian lungfish) can swallow atmospheric air by rising to the surface of the water. Lepidosiren paradoxa and the African lungfish hibernate during dry periods. All lungfish have some commercial significance. Fishing for Australian lungfish is prohibited. Fossil remains of lungfish are known from the Devonian; they are found all over the world in the form of separate dental layers. They were widely distributed and had many characteristics in common with Crossopterygii fishes; they had the torpedolike shape characteristic of free-swimming fishes, an unevenly lobed (heterocercal) tail, and short unpaired fins (in representatives of the genus Dipterus). However, as early as the Upper Devonian, the body became more elongated in form, the unpaired fins became longer and merged with one another, and the tail became evenly lobed, or diphycercal (in Phaneropleuron). In addition, one may note in the evolution of lungfish a reduction of ossification in the skull and in the dentine layer of the integumental bones, and a decrease in their number. The genus Ceratodus, closely related to the present-day Australian lungfish, existed from the Triassic. Lungfish have apparently lived in fresh waters during the entire length of their existence.

REFERENCES

Nikol’skii, G. V. Chastnaia ikhtiologiia, 3rd ed. Moscow, 1971.
Osnovy paleontologii: Bescheliustnye, ryby. Moscow, 1964.

A. A. SVETOVIDOVA