This is the largest of the сnidarian classes and contains over 6000 species, Although the anthozoans are polypoid, they differ considerably from hydrozoan polyps The I mouth leads into a tubular pharynx that cxtendil more than halfway into the gastrovascular cavil (Fig. 5-34). The gastrovascular cavity is divideded longitudinal mesenteries, or septa, into radiating compartments, and the edges of the mesentery bear nematocysts. The gonads, as in the scyphozoans are gastrodermal, and the fibrous mesoglea contains cells. The nematocysts, unlike those of hydrozoans and scyphozoans, do not possess an opercullum, or lid. Some anthozoan nematocysts have a | three-part tip that folds back on expulsion; іn оthers, the thread appears to rupture directly through) the end of the capsule. In order to simplify the survey of this class, we will deal with the sea anemones, the stony corals and the octocorallian corals separately.