• Norwegian: nesledyr


All cnidarians have venomous cells (cnidocytes) used to catch prey like fish and crustaceans, or as a defense against other predators. The cnidocytes are capable of firing a structure containing toxin into the prey. Some cnidarians are deadly even to people. They usually come in one of two common shapes; as swimming medusae or as a polyp attached to the substrate. They are all radially symmetrical around a single mouth bordered with tentacles and a body cavity used for digestion. Some, like for instance corals and sea pens, form colonies. Cnidarians have a nerve system, some even have simple eyes.


The phylum Cnidaria includes more than 9000 aquatic, mainly marine species, organized in the following classes: