Although the phylum Chordata does not have an inordinately large number of species (about 45,000), its members have been very successful at adapting to aquatic and terrestrial environments throughout the world.
1. Bilaterally symmetrical, deuterostomate animals
2. Four unique characteristics present at some stage in development: notochord, pharyngeal slits or pouches, dorsal tubular nerve cord, and postanal tail
3. Presence of an endostyle or thyroid gland
4. Complete digestive tract
5. Ventral, contractile blood vessel (heart)