Subphylum Vertebrata

Vertebrates, also called the "higher chordates," are set apart from the other two subphyla by one key developmental fact: they possess a notochord only during the embryonic stage. In the adult, the notochord is replaced by a cartilaginous or bony vertebral column, built up of vertebrae. This is the basis of the rule that all vertebrates are chordates, but not all chordates are vertebrates — Urochordata and Cephalochordata are chordates that never develop a backbone.

Vertebrates possess paired appendages (fins or limbs), and their skin is protected by a covering that varies by class — scales, feathers, hair, claws or nails. Respiration is aerobic and may take place through gills, skin, the buccopharyngeal cavity, or lungs depending on the class. All vertebrates have a ventral, muscular heart with two, three or four chambers, and kidneys for excretion and osmoregulation. …