Tunicate

Tunicates have two openings in their body cavity: an incurrent and an excurrent siphon. The incurrent siphon takes in water plus any food it contains, and the excurrent siphon expels wastes plus sieved water. The primary food source for most tunicates is plankton that gets entangled in mucus secreted from the endostyle. The tunicate's pharynx, or branchial sac, is lined with ciliated epithelium. The action of the cilia passes food particles and plankton down to the esophagus and also passes the stream of water from the inhalant to the exhalant siphon. The gut is U-shaped and also ciliated, and the anus opens into the dorsal or cloacal part of the peribranchial cavity near the atrial aperture, where the constant stream of water carries wastes to the exterior.