A phylum of animals characterized by a hollow dorsal nerve cord and, at some stage in their development, a flexible skeletal rod (the notochord) and gill slits opening from the pharynx. There are three major groups: the Urochordata (sea squirts), Cephalochordata (lancelets), and craniates.

http://www.tolweb.org/Chordata Tree of Life web page outlining main characteristics and phylogeny of chordates