Provides much of the propulsive force in many aquatic species. The digestive tract in most nonchordates extends nearly the whole length of the body. Urochordata are called tunicates. Entire animal is cloaked in a tunic made of a celluloselike carbohydrate. Most are sessile marine animals which adhere to rocks, docks and boats.
Some species are planktonic, while others are colonial.
The tunicates are filter feeders. Seawater enters through an incurrent siphon, passes through the slits of the pharynx into a chamber called the atrium , and exits via an excurrent siphon, the atriopore . Food filtered from the water by a mucous net of the pharynx is moved by cilia into the intestine. The anus empties into the excurrent siphon. When disturbed, tunicates eject a jet of water through the excurrent siphon, so they are commonly called sea squirts.