Subphylum Urochordata: (tunicates or sea squirts). These are a diverse group of marine chordates with planktonic tadpole-larvae showing all four phylum characteristics, and highly modified sessile filter feeding adults with body walls composed of cellulose-like tunicin, and incurrent and excurrent siphons serving an enlarged filtering pharynx. They may be found living alone or in colonies. What chordate features are shared by the larvae and adults? What function does the pharynx serve?