Chordata

Chordata, a phylum or branch of the animal kingdom, characterised by the possession of a rod (the notochord) underlying the central nervous system, and by visceral clefts, i.e. passages at the sides of the head or neck opening outwards. Either or both of these characters may be temporary or permanent. The Chordata are arranged in three groups: - 1. Cephalochordata, of which Amphioxus (q.v.) is the only example. 2. Urochordata, with two subdivisions - (1) Perennichordata, in which the notochord is retained through life, as in Appendicularia (q.v.); (2) Caducichordata, in which the caudal notochord is present in the larva only, or is not developed. 3. Craniata, containing the true Vertebrates (q.v.).