Question

Write a short note on dipnoi.

Answer 1

Hint: Dipnoi is an order which specifies to bony lung fishes. It is the subclass of Sarcopterygii. They originated in the early Devonian period. Fishes belonging to this order are obtained from the mud of the dried river and are used as food by humans.

Complete step by step answer:
Dipnoans are one of the orders in the taxonomic classification. They refer to the fishes that are living in freshwater and mainly bony in nature. They are provided with plate teeth the respiration in these fishes takes place by means of both gills and lungs. Presence of the lungs for respiration shows that they are former to the amphibians. Hence, they are known as lung fishes.
These fishes are provided with swim bladder which are the modification of lungs, used for the exchange of gases in the water and it helps to maintain the buoyancy to swim in the water. These fishes are long and appear similar to snakes but morphology does not dictate evolutionary relationships. These are regarded as the closest living relatives of tetrapods and have many characteristics similar to them. These lung fishes can live even when the pool dries, by digging into mud and covering themselves with the mucous layer. At these times when there is no water, they respire through the swim bladder.

Thus, the option (D) is the correct one.

Note:
Most of these fish grow to the larger weight of up to $10\,Kg$ and look like snakes with the paired fins. An example for these types of fishes are Queensland, Protopterus aethiopicus etc. Of which, Protopterus aethiopicus are the largest of lung fishes.