Jellyfish are aquatic animals that can cause a "sting" when they come into direct contact with humans or other animals. Injuries usually occur when humans are swimming or wading in ocean waters and accidentally come into direct contact with these marine creatures. The stingers are usually located at the ends of the tentacles and contain poisons that can be toxic to humans. In most cases, however, the poisons only cause injury to the part of skin that comes into direct contact with the tentacles.
Jellyfish are invertebrate marine animals. There are nearly 9,000 species of jellyfish, which can be broken down into 3 main classes:
The hydrozoans include feathery hydroids, fire coral, and the Portuguese man-of-war. The Portuguese man-of-war lives in the Atlantic Ocean along the East Coast of North America, as well as in the Pacific and Indian oceans. The tentacles of these enormous animals can reach up to 100 feet in length. In addition, even detached tentacles are capable of causing stings for up to 2 weeks.
True jellyfish (scyphozoans) are the most common species of jellyfish in North America. As a rule, their stings are considerably less toxic than the hydrozoans and are usually limited to eruptions of the skin where contact took place. The box jellyfish, however, is an exception. These animals are found only in the waters of the Indo-Pacific. Their sting is so toxic that the Commonwealth Serum Laboratories of Australia keep antivenom, which neutralizes the toxin, available for people who are injured by them. More than 60 deaths have been confirmed as a result of box jellyfish stings.
Sea anemones and corals (anthozoans) are also related to jellyfish but are usually minimally poisonous to humans. No deaths have been reported as a result of a sting from a sea anemone or coral.