Final answer:
Hemichordates are not members of the phylum Chordata; instead, they fall under the group Ambulacraria. Chordata includes vertebrates, tunicates, and lancelets, all of which share the presence of a notochord.
Step-by-step explanation:
The group that is not a member of the phylum Chordata is hemichordates. The phylum Chordata includes vertebrates as well as two invertebrate clades: Urochordata (tunicates) and Cephalochordata (lancelets). Although hemichordates share some characteristics with chordates, such as pharyngeal slits and a dorsal nerve cord, they lack a notochord, which is a defining characteristic of chordates. Instead, hemichordates belong to a different group called Ambulacraria, which also includes echinoderms.