Cnidocyte

Nomarski micrograph of a ruthenium red-stained nematocyst from *Aiptasia pallida*, the pale anemone. The red dye stains the polyanionic venom proteins found inside the capsule of this partially-discharged nematocyst.

A cnidocyte (also known as a cnidoblast) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida (pl.: cnidae)) that can deliver a sting to other organisms. The presence of this cell defines the phylum Cnidaria (corals, sea anemones, hydrae, jellyfish, etc.). Cnidae are used to capture prey and as a defense against predators. A cnidocyte fires a structure that contains a toxin within the cnidocyst; this is responsible for the stings delivered by a cnidarian. Cnidocytes are single-use cells that need to be continuously replaced.