Sea squirt, any of a group of marine animals (class Ascidiacea), also known as ascidians, that squirt water when squeezed. The sea squirt's body is enclosed in a jellylike coat; there are two openings, at the top and side, from which the water squirts. When the sea covers it, the sea squirt takes water in through one opening sieving off minute food particles. The waste water is passed out of the other opening. Sea squirts are found alone or in clusters, sometimes with individual animals joined together. Each sea squirt is both male and female; in the larval stage it looks like a tadpole.