Organisms in the subphylum of Urochordata, sometimes known as the Tunicata, are commonly known as "sea squirts." The body of an adult tunicate is essentially a sack with two siphons through which water enters and leaves. Water is filtered inside the sack-shaped body.
tunicates
Most of the body of the adult is occupied by a very large pharynx with numerous gill slits that act as a sieve for food. Water taken into the incurrent siphon enters the pharynx and passes out through the gill slits, leaving food particles trapped in the pharynx. The sea squirt larva is a free-swimming animal resembling a tadpole. There are two other classes of tunicates, both consisting of small planktonic animals. The salps (Thaliacea) metamorphose into barrel-shaped adults that swim by muscular contractions. The larvaceans (Larvacea) are neotenous, that is, they achieve sexual maturity and reproduce without losing the larval form.