A sea nettle is a type of stinging jellyfish found in both the Pacific and Atlantic oceans. These jellies include several species, all in the Chrysaora genus. The most extensively studied species are Chrysaora fuscescens, common to the Pacific waters, and Chrysaora quinquecirrha, commonly found in the Atlantic.
Jellyfish are marine creatures that usually consist of a bell or disc shaped upper area and many long, trailed tentacles and oral arms. Though they have a nervous system, they have no brain. Jellyfish also have basic digestive and respiratory systems. Trailing from the upper disc are oral, or mouth, arms that are responsible for bringing food to the mouth portion of the upper area, as well as tentacles which, in stinging jellyfish, contain the toxin that is injected into the animal's prey or potential predators.
Depending on the species, the bell of the sea nettle may be between 6 and 18 inches (15.24–45 cm) across. The four mouth arms can be up to 15 feet (4.6 m) long. The numerous tentacles are often slightly shorter than the arms. The thin tentacles are located around the outer edge of the bell and can be easily distinguished from the fluffy, frilled arms they encircle. These tentacles contain stinging cells.
The sea nettle uses its tentacles both for hunting and for defense. It generally eats zooplankton, larval fishes, and other jellyfish. When its prey touches a tentacle, the stinging cells inject the toxin into the animal. Then, the prey is moved to the oral arms, where the food is transferred to the jellyfish's mouth.
When the sea nettle senses threat, it can also use the stings for defense. The toxin paralyzes large animals and can cause death in small creatures. In humans, sea nettle stings normally cause severe pain and a rash, but can possibly be fatal if the victim is allergic to the toxin or in cases of multiple stings. Jellyfish swim in swarms, so people are always advised to avoid areas where they can be seen or are known to be.
Chrysaora fuscescens, the most studied species of sea nettle in Pacific waters, reaches up to 11 inches (28 cm) across. A golden brown color, these jellyfish are most commonly seen along the Pacific coast in the United States during winter months. The most studied species in the Atlantic waters, Chrysaora quinquecirrha, is most commonly found along the US Atlantic coast in the summer and is the jellyfish responsible for most human stings in many areas.