Dipnoi, The Lung Fishes

Dipnoi means double breathers fishes. As they can respire through gills and lungs as well. Dipnoi fish evolved during mid Devonian period probably as an offshoot of the crossopterigian stem and flourished moderately in permian and triassic and later became rare. The earliest recorded fossil lung fish is “Dipterus” of middevonian and Cerotodus of triassic.They are characterized by short jaws, crushing plate from teeth, internal nares, reduced exo- and endo- skeleton, and diphycercal tail.
The air bladder act as lungs, so called ‘lungs fishes’. Air sacs are functional with related exchanges in the circulatory system and in the heart.
Distribution of Dipnoi: Today dipnoi have only three surviving genera of lung fishes are Protopterus, Lepidosiren and Neoceratodus . All they are inhabitants of fresh water rivers.
Protopterus lives in the mud of great Nile river and other lakes of tropical S. Africa. Therefore they are commonly known as ‘African lung fish’. Lepidosiren paradoxa lives in Amazon river and its tributaries of south America. Therefore it is called as ‘South American lung fish’ or ‘Amazon lung fish’. Neoceratodus forestri is found only in the Burnett and Mary rivers of Queensland in Australia, so commonly called as ‘Burnett Salmon’ or Australian lungfish. Neoceratodus is the only living genus of the family Ceratodontidae, the other being extinct Ceratodus. These are the example of discontinuous distribution and divergent evolution. Beside swimming in water by undulating body movements they also crawl on the bottom using their paired fins like legs. They can survive in draught by aestivating in a mucous cocoon buried in the bottom mud of their habitat. Parental care is more pronounced in males, they guard their eggs. Male periodically leaves the nest to engulp atmospheric air and diffuses to the vicinity of eggs to aerate them.
Classification of order Dipnoi.
Dipnoi has only three genera all over the world and they are subdivided in to two suborders-
1. Monopneumona- Single lung e.g. Neocerotodus forsteri (Australian lung fish).
2. Dipneumona- Double lungs e.g. Protopterus and Lepidosiren
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