First of all, all kinds of living organisms which are eukaryotes and compose of numerous cells and can sexually reproduce are known as animals. All animals have a unique role to play in maintaining the balance of nature.

A lot of animal species exist in both, land and water. As a result, each of them has a purpose for their existence. The animals divide into specific groups in biology. Amphibians are those which can live on both, land and water.

Reptiles are cold-blooded animals which have scales on their body. Further, mammals are ones which give birth to their offspring in the womb and have mammary glands. Birds are animals whose forelimbs evolve into wings and their body is covered with feather.

They lay eggs to give birth. Fishes have fins and not limbs. They breathe through gills in water. Further, insects are mostly six-legged or more. Thus, these are the kinds of animals present on earth.