The vertebrates are further classified into subgroups on the basis of server characters such as:

•The kind of exoskeleton or endoskeleton.

•Number of chambers in heart.

•The kind of respiratory organs.

•The method of reproduction and giving birth to young ones.

On the basis of above mentioned characters the vertebrate is divided into following classes.

1) Pisces (fishes)- Exoskeleton of scales; two-chambered heart; breathing through gills.

2) Amphibia – Three chambered heart; breathing through gills only in larva; skin slimy.

3) Reptilia- Exoskeleton of scales or scutes; three chambered heart; laying eggs outside the water.

4) Aves (birds)- Exoskeleton of feathers; four chambered heart; lays eggs.

5) Mammalia- Exoskeleton of hair; four chambered heart; external ears; give birth to young ones.