Vertebrates that lack jaws are known as Agnatha, and those vertebrates with jaws are called Gnathostomata. The Gnathostomata is divided into two superclasses based on the presence of limbs or fins for locomotion. Those organisms that have limbs for locomotion are called Tetrapods. Those organisms that bear fins for locomotion are called Pisces. The Pisces are aquatic, whereas the Tetrapods are mostly terrestrial.
