The ancient extant Lungfish can breathe oxygen from air and can remain in ground for almost 4 years. These fishes have long life. As the name suggests, they have one or two lungs which help them to breathe atmospheric oxygen.

The Dipnoi, a group of sarcopterygiian fish is commonly known as lungfish. They have modified swim bladder that helps them for buoyancy in swimming. These fishes are able to survive even in dry pools by burrowing into mud and sealing themselves within a mucous lined burrow. Only a single hole will be left for breathing to sustain in the mud. They use swim bladder to breathe air instead of gills and also reduce their metabolic rate substantially.

These primitive living fishes first appeared in the Early Devonian Epoch (about 419.2 million to 393.3 million years ago). Historically, these lungfishes are also known as salamanderfish.

All lungfishes have snake-like bodies. The base colour is brown, having darker speckles all over. Their eyes are too small and are in blue colour.

The fossil record shows the existence of seven known families of lungfish. Among these, only three of them survive now at Africa, South America and Australia.

Australian Lungfish (Neoceratodus forsteri)

These may grow up to 4 feet long. They have large flipper-like fins and large scales that distinguish them from its other species.

These fishes have the ability to survive for prolonged periods out of water using their lungs to breathe.

African Lungfish (Protopterus aethiopicus)

Afican lungfishes are the largest which can grow to a length of about 7 feet that have two lungs with external gills, which they lose at a certain age.

They can live prolong periods without water into a mud creating a mucous cocoon. This is known as aestivation.

South American Lungfish (Lepidosiren paradoxa)

The South American Lungfish is different due to its elongated body and may grow up to 4 feet. These are atmospheric air breather,still it does not create mucous cocoon while undergoing aestivation.

Primitive lungfish groups retain marginal teeth and an ossified braincase while derived fishes show a significant reduction in the marginal bones and a cartilaginous brain case.

They have a highly specialized respiratory system. Their distinct feature is that the lungs are connected to the larynx and pharynx without a trachea. These lungfish species have two lungs with an exception for Australian Lungfish.

As the water passes through the gills of lungfish, they use a buccal pump. This is a unidirectional path flow through the mouth and gills. During air breathing, the sixth gill is used for respiration and also for passing the deoxygenated blood before reaching the lung.

The lungfishes are close relatives of tetrapods as they characterise many similarities with them. Their lungs are homologous to the lungs of tetrapods.

Being omnivorous, they eat aquatic animals including their own species. When they become adults, their teeth fuse together to form tooth plates to chew their food.

A Queensland lungfish at the Shedd Aquarium in Chicago was part of the permanent live collection from 1933 to 2017.