Coelenterate

Coelenterate, phylum of primitive, invertebrate animals, now renamed the Cnidaria (the C is silent). It includes anemones, corals, jellyfish, the freshwater hydra, and many others. The basic body form is a two-layered sac, with a mouth at one end surrounded by a ring of tentacles. Food is captured and poisoned by means of nematocysts, or “stinging cells,” in the tentacles. Coelenterates exist in two forms. Anemones, corals, and hydra are polyps, which are anchored and tubular. Jellyfishes are medusae, or free-swimming.