Cnida
The cell which produces the cnida is variously called a cnidocyte, cnidoblast, or nematocyte. It is highly specialised for just one function. Each nematocyte 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.