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Vertebrata

Definition: One of the grand divisions of the animal kingdom,
comprising all animals that have a backbone composed of bony or
cartilaginous vertebrae, together with Amphioxus in which the backbone
is represented by a simple undivided notochord. The Vertebrata always
have a dorsal, or neural, cavity above the notochord or backbone, and a
ventral, or visceral, cavity below it. The subdivisions or classes of
Vertebrata are Mammalia, Aves, Reptilia, Amphibia, Pisces,
Marsipobranchia, and Leptocardia.