A group of simple chordates, including sea squirts (class Ascidacea) that live attached to rocks, and the salps (class Thaliacea) that float in the sea. Tunicates are small marine animals, cylindrical, spherical, or irregular in shape, ranging from several millimetres to over 30 cm in size. They have a saclike cellulose tunic covering the body; water is drawn in through a siphon and food particles are filtered out. The free-swimming tadpole-like larvae show the major characteristics of all chordates. They subsequently undergo metamorphosis, losing their chordate features and becoming adults. One group (class Larvacea) retain their larval characteristics throughout life.