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The nematocyst is the stinging apparatus of the phylum Cnidaria. The whole life-style of the phylum is based on this device, which enables the animals to catch their prey.

Diagram of nematocyst discharging

The cell which produces the nematocyst is variously called a cnidocyte, cnidoblast, or nematocyte. It is highly specialised for just one function. Each cell contains an organelle with a hollow, coiled, thread-like structure. The outside of the cell has a hair-like trigger. When the trigger is touched, the shaft of the cnidocyst fires like a harpoon. It penetrates the prey, and the hollow thread comes with it. This takes no more than a few microseconds. After penetration, the toxic content of the nematocyst is injected into the target. The rapid activity of the injected neurotoxins paralyzes the mobile prey, thus allowing the sessile cnidarian to devour it.

Types of nematocysts

Over 30 types of nematocytes are found in different cnidarians. They can be divided into the following groups:

  1. Penetrant: a harpoon-like structure used to penetrate
  2. Glutinant: a sticky surface used to stick to prey
  3. Volvent: a lasso-like string that is fired at prey and wraps around a cellular projection on the prey
  4. Ptychocyst: a special type of nematocyte found on burrowing (tube) anemones, which help create the tube in which the animal lives.

Depending on the species, one or several types can appear simultaneously on the organism.