Sea squirt, also called ascidian, is a group of sea animals that spend their adult lives attached to stones, shells, and other fixed objects. Adults have leathery bottle-shaped bodies with two openings. They feed by filtering plankton (tiny water animals) from the water. The sea squirt feeds by drawing water into its digestive tract through one of its body openings, the incurrent siphon. The animal squirts out the water from the other opening, the excurrent siphon. Some sea squirts live alone, but others live in colonies.
Sea squirts go through a larval (immature) stage before they become adults. The larva looks like a tadpole and can swim about. It has a notochord (elastic rod) that extends through the tail. Because of this “backbone,” scientists think sea squirts are relatives of the simplest fishlike animals, lancelets and lampreys. In a few days, the larva loses its tadpole shape. Soon, the sea squirt develops into its adult form.
