This phylum is divided into three subphyla.  Two of these subphyla are composed of invertebrates (animals with no bones) and one is composed of vertebrates (animals with backbone). 

The following are the four characteristics that all chordates share at least sometime in their lives:

(1) A notochord; a flexible rod running along the back of the animal that eventually forms into the vertebrae, (2) a dorsal nerve cord (chordate's brain and spinal cord); (3) gill structures, and (4) a post anal tail.

The six classes of vertebrate chordates will be presented here. 

Class Osteichthyes (bony fish), Class Chondrichthyes (fish with cartilage), Class Amphibia (frogs), Class Reptilia (snakes), Class Avia (birds), and Class Mammalia (mammals).