Tunicata

[Sarah]

A grand division of the animal kingdom, intermediate, in somerespects, between the invertebrates and vertebrates, and by somewriters united with the latter. They were formerly classed withacephalous mollusks. The body is usually covered with a firm externaltunic, consisting in part of cellulose, and having two openings, onefor the entrance and one for the exit of water. The pharynx isusually dilated in the form of a sac, pierced by several series ofciliated slits, and serves as a gill.