Cnidários

The Cnidaria phylum (from the Greek knidos - stinging) encompasses more than 10,000 species, which are found mostly in a marine environment, with anemones and jellyfish being the best-known examples.

They have cells that sting, cnidocytes, which they use to inject a spine, called a nematocyst, within which there is a toxin used as a defence mechanism and for capturing prey.