chordate science definition

Any of a large group of animals of the phylum Chordata, having at some stage of development a notochord (flexible spinal column) and nerve cord running along the back, a tail stretching above and behind the anus, and gill slits. Chordates probably evolved before the Cambrian Period and are related to the hemichordates, echinoderms, and chaetognaths. The vertebrates, tunicates, and cephalochordates are the three main groups of chordates.