Jellyfish sting in order to catch their prey. They also sting to keep other animals from eating them.

Jellyfish tentacles and oral arms are covered with thousands of stinging cells. Inside each stinging cell is a hollow tube. This tube looks like a coiled thread. When an animal touches the stinging cell, the tube fires out to sting the prey.All cnidarians have stinging cells. But the cells may work in different ways to deliver their stings. Some stings pierce an animal’s skin. These stings release a poison. The poison paralyzes the prey so that it cannot move. Other stings are very long. They wrap around the prey and trap it.

A jellyfish’s sting is a good defense. But it does not protect a jellyfish from all sea animals. Some animals that eat jellyfish aren’t affected by the stings. They include sea slugs, ocean sunfish, and sea turtles.

Jellyfish are not fish—although they do spend their entire lives in water. Rather, these soft-bodied animals and their relatives are called cnidarians (ny DAIR ee uhnz). Cnidarians all have one thing in common: stinging cells. Some people call these creatures stingers.

One kind of stinger is a compass jellyfish. Its body is shaped like an umbrella. There are also cnidarians that don’t look at all like the compass jellyfish. Some have square shapes, while others look like flowers or plants.

Stingers live in all the oceans in the world. Some live in warm tropical waters. Others live in the icy waters of the Arctic. A few stingers even live in fresh water.

You may have seen jellyfish floating near the surface of the water. In fact, most jellyfish live in the upper waters of the ocean—the sunlit zone. At night, these jellyfish may sink down into deeper waters. Some stingers live their entire lives in deeper waters. Still others—such as sea anemones and corals—attach themselves to the ocean floor.

Jellyfish may swim or drift along with the ocean currents. Some swim alone. Others are found in huge groups, or shoals (SHOHLZ). Wherever they are, these unusual creatures are always moving.

Sea wasps have powerful stings that can cause severe burns. But the Australian sea wasp is the most feared jellyfish of all. Its poison is deadlier than any snake venom. And it can kill large animals, including humans, in as little as three minutes.

The Australian sea wasp may grow as large as a basketball. And its threadlike tentacles can be as long as 15 feet (4.6 meters). But the bell is clear and very hard to see in the water. Australian sea wasps pose a special threat to swimmers. The reason is that these jellyfish often feed close to the shore where people swim.

Even Australian sea wasps, however, have enemies. Large sea turtles feed on them. The sea turtle’s tough skin and stomach may protect it from the jellyfish’s sting. But scientists aren’t really sure how the sea turtle can swallow the jellyfish without being poisoned.

Sea wasps are not like most other jellyfish. Sea wasps are the only stingers that have eyes. But scientists aren’t sure what sea wasps can see. Like other stingers, sea wasps don’t have brains. So, it is hard to figure out how these stingers use their eyes. But they probably use them to find prey and keep away from their predators.

Sea wasps are different from most jellyfish in other ways, too. Sea wasps don’t have oral arms. Instead, they have four groups of tentacles. The tentacles are found at each corner of their box-shaped medusa. Because of their unusual shape, these stingers are also known as box jellyfish.

Some jellyfish belong to the class Scyphozoa; these jellyfish are usually larger than the polyps from which they develop. Other jellyfish belong to the class Hydrozoa; these jellyfish are usually smaller than their polyps. Jellyfish belong to the phylum Cnidaria.