These characteristics are always found at some embryonic stage, although they may be altered or may disappear altogether in later stages of the life cycle. Hickman, C.P. and L.S. Roberts. Biology of Animals, Sixth Edition .
Pharyngeal gill slits present at some stage in life cycle.
Postanal tail , usually projecting beyond the anus at some stage but may or may not persist. Segmented muscles in an unsegmented trunk. Complete digestive system. There are approximately 1500 described species of these marine living chordates. They are commonly called tunicates because of the tough, nonliving tunic that surrounds the animal.