The chordates have a notocord, dorsal hollow nerve cord, gills, post anal tail and muscle blocks. Chordates have these characteristics at one time in their life.
Chordates also have bilateral symmetry.
We are most familiar with most of these animals, however, subphylums urochordata and cephalochordata are much different from chordates like we know. Urochordates are the sea squirts. The sea squirts do not appear to have any of the characteristics of chordates, but the larval stage does. Cephalochordates are lancelots, and they are similar to fish. They bury everything but their mouthes in the sand and are filter feeders.