Stinging Tentacles

Stinging Tentacles
A group of ocean animals called cnidarians also use stings for predation and self-defense. This group includes corals, jellyfish, and anemones. Most are harmless to humans, or cause little more than a rash. Some cnidarians, however, contain venom strong enough to sicken or kill a human. The box jelly, also called a sea wasp, is among the most deadly. It lives off the coast of Australia. Its venom causes extreme pain, and a bad sting can kill a human in less than five minutes.

Cnidarians’ stingers are called nematocysts. They are located on the animals’ tentacles. Hundreds or even thousands of nematocysts can be found on one tentacle, depending on the species. A box jelly’s tentacle, which can be 9 feet (3 meters) long, contains millions of nematocysts.

There are three kinds of nematocysts. One kind makes a gluey substance that sticks to prey. A second kind shoots out threads that loop around prey like coils of rope. The third kind is venomous and works like a miniature harpoon. An animal may have one or more kinds, depending on its species.

When an animal—either predator or prey—comes in contact with a tentacle with venomous nematocysts, the nematocysts launch their harpoons. Out shoots a tiny barb attached to a twisted thread. The barb jabs the animal’s body. The thread untwists, pushing the barb into the skin. Venom flows through the thread and into the animal.

The venom paralyzes or kills prey so that the cnidarian can drag it to its mouth and eat it. Cnidarians eat a variety of prey, depending on their size. Anemones look like plants rooted in sand and mud or on rocks and coral reefs. However, they are animals, and they feed on small fish, crabs, and shrimp. Coral polyps, which make up coral reefs, feed on tiny animals called zooplankton that drift in the water. Many jellyfish feed on fish and shrimp.