Tunicate

tunicate, also called urochordate, any member of the subphylum Tunicata (Urochordata) of the phylum Chordata. Small marine animals, they are found in great numbers throughout the seas of the world.

Adult members are commonly embedded in a tough secreted tunic containing cellulose (a glucose polysaccharide not normally found in animals). The less modified forms are benthic (bottom-dwelling and sessile), while the more advanced forms are pelagic (floating and swimming in open water). A characteristic tadpole larva develops in the life cycle, and in one group (the appendicularians, or larvaceans) the adult closely resembles this larva, which has many features in common with other chordates. Most chordate features disappear at metamorphosis.