Encyclopaedia Of Chordate Zoology

All beings of the phylum Chordata have branchial clefts in the pharynx, notochord and dorsal neural tube. In chordates the nervous system is dorsal and highly cephalized while in most invertebrates the nervous system is ganglial and ventral. In vertebrates the notochord disappears and gives birth to the spinal column (vertebral column). In protochordates the notochord remains for the rest of the life. The tubular and dorsal nervous system of chordates is related to the cephalization in these ani