What are Corals and Coral Reefs
Cross-sectional view of an anthozoan polyp, the sea anemone Megalactis sp., at the level of the actinopharynx. (Image copyright © 2000 Adorian Ardelean).
The actinopharnx (stomodeum) is an irregularly shaped tube extending from the mouth of the polyp into the digestive cavity, or coelenteron. Most corals possess two biradially arranged longitudinal evaginations, the siphonoglyphs. The siphonoglyphs are lined with flagellated cells which drive water into the coelenteron. Longitudinal sheets of tissue, the mesenteries, extend radially from the body wall. Some extend all the way to the actinopharynx. Mesenteries attached to the siphonoglyphs contain muscles which allow the polyp to retract. The mesenteries also contain specialized cells which function in digestion. The calcified radial septa of the scleractinian skeleton lie between pairs of mesenteries.