Introduction of 'Dipnoi'

Dipnoi are also called lung fishes. They have the peculiar character. They first appeared in the mid Devonian deposits, flourished in Permian and Triasic period and became rare. They are actually the  fishes having the skeleton made up of bones . They belong tot he subclass choanichthyes. Actually all the fishes use to respire with  the help of gills but the most interesting and peculiar character of  these fishes is that they have lungs by which they breathe in oxygen during respiration. The living Dipnoans are represented by three genera only. These show the discontinuous distribution. These genera are the following:
1.Protopterus from Africa, 2. Lepidosiren from South America and 3. Neoseratodus from Queensland - Australia.
Dipnoi are so known as lung fishes that they have air filled bladder like structures in their body called air bladder which act as lung. These fishes also possess gills. So, these fishes exhibit the double mode of breathing, i.e. breathing from gills and breathing from lungs or air bladder.