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 a type of cell containing a large secretory organelle called a cnidocyst, that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ejects the toxin-containing cnidocyst which is responsible for the stings delivered by a cnidarian. The presence of this cell defines the phylum Cnidaria, which also includes the corals, sea anemones, hydrae, and jellyfish. Cnidocytes are single-use cells that need to be continuously replaced.