The phylum includes several classes:
- Mammalia - the mammals
- Aves - the birds
- Reptilia - The reptiles
- Amphibia - the amphibians (such as frogs, newts and salamanders)
- Pisces - the fish
Scientists believe that the chordata are closest to the arthropoda (shelled, joint-legged animals such as insects and crustaceans), echinodermata (spiny-skinned animals such as starfish and sea urchins), and annelida (earthworms) in biology, due to common features such as segmentation, which are not seen in other phyla such as the mollusca (molluscs) or coelenterata (jellyfish and sea anemones).