The lung fish is divided into different classes. These include neoceratodus, lepidosiren and protopterus. All of them have a heart which is 3 chambered. The neoceratodus is known as Australian lung fish. It occurs in the rivers of Australia. It has cycloid scales which cover the body. They are also present on the fins. It mainly respires by gills but can switch to lungs if the conditions are adverse. The lepidosiren is known as South American lung fish. It occurs in the rivers of America. It has cycloid scales which cover the body. It mainly respires by gills but can switch to lungs if the conditions are adverse and has couple of lungs. The fins are paired and there is a union between a dorsal and caudal fin. In summer season it goes under aestivation. The protopterus is known as African lung fish. It occurs in the rivers of Africa. It resembles like an eel. The gills are not properly formed. They can switch to lungs if the conditions are adverse and has couple of lungs for this purpose. The fins are paired and filamentous. In summer season it goes under aestivation.
The latimeria is also known as a living fossil. It occurred in the coast of South Africa and fishermen were the first to locate it. It is the oldest fishes and forms a connecting link between fishes and amphibians.
