The Subphylum Vertebrata has been classified into two superclasses, namely, Agnatha and Gnathostomata, on the basis of presence or absence of jaws and paired appendages. Agnatha members do not have jaws and paired appendages while Gnathostomata members bear jaws and paired appendages. Superclasses have further been classified into Classes Pisces, Amphibia, Reptilia, Aves and Mammalia.

The major characteristics used to classify are :

• The kind of exoskeleton or endoskeleton,
• The kind of respiratory organs
• The method of reproduction and giving birth to young ones.

It can be summarised as follows:

• Exoskeleton of scales; Endoskeleton of cartilage’ or bones; Breathing through gills – Pisces (fishes).
• Breathing through gills only in larva; Skin slimy – Amphibia.
• Exoskeleton of scales; Laying eggs outside the water-Reptilia.
• Exoskeleton of feathers; Lay eggs; Flight possible – Aves (Birds).
• Exoskeleton of hairs; External ears ; Give birth to young ones -Mammalia.