sea squirt

Any solitary or colonial-dwelling saclike chordate of the class Ascidiacea. A pouch-shaped animal attached to a rock or other base, it draws in food-carrying water through one siphon and expels it through another after straining it through numerous gill slits. The young are free-swimming tadpole-shaped organisms, which, unlike the adults, have a notochord.

Sea squirts have transparent or translucent tunics made of cellulose. They vary in size from a few millimetres to 30 cm/12 in in length and are cylindrical, circular, or irregular in shape. Their defences against predators include sulphuric acid secretion and the accumulation of vanadium, a toxic heavy metal.