nematocyst In Cnidaria, part of a cnidoblast; it is a pear-shaped sac with a lid (operculum), the outer end of the sac being extended to form a long, hollow thread which is stored coiled within the sac, immersed in a fluid. On stimulation of a sensory bristle (a cnidocil) the thread is expelled, as a weapon or to capture or hold prey, depending on the type of nematocyst. Some nematocysts are barbed and some inject venom.

nematocyst In Cnidaria (sea anemones, jellyfish, and corals), part of an epidermal cell (cnidoblast), comprising a sac with a lid, the open end of the sac being extended into a long, hollow thread. The thread is stored inside the sac, coiled and immersed in a fluid. When a sensory bristle (cnidocil) is stimulated, the thread is expelled to capture or hold prey or as a weapon, depending on the type of nematocyst. Some nematocysts are barbed and some inject venom.

nematocyst See thread cell.