Chordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having,
for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and
a post-anal tail. The phylum Chordata consists of three subphyla: Urochordata, represented by tunicates; Cephalochordata,
represented by lancelets; and Craniata, which includes Vertebrata.
