Urochordata
Urochordata is a marine phylum of chordates characterized by a tough outer covering called a tunic, which gives them their alternate name, Tunicates. They are filter feeders that possess a notochord in their larval stage, but it is often lost in the adult form. Urochordates typically have a barrel-shaped body with two siphons for water intake and expulsion. They are considered to be one of the most primitive groups of chordates.