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The jellyfish has no bones. Instead, its body, shaped like an open umbrella, is supported by a thick layer of a jellylike substance called mesogloea. The jellyfish's tentacles contain stinging cells that inject a paralyzing poison into its prey.

Some jellyfish can inflict painful and even dangerous stings to people. Jellyfish called sea wasps inject their victims with a poison that is deadlier than any snake venom. Some people have died less than three minutes after being stung by a sea wasp. Sea wasps are found near the coasts of northern Australia and the Philippines.

The sea wasp is a jellyfish found mainly in the waters of the Great Barrier Reef off the coast of Australia. A severe sting from a sea wasp can kill a person within three minutes.

Jellyfish are classified as cnidarians, a phylum that includes corals, sea anemones, and hydras. Large jellyfish make up the class Scyphozoa «SY fuh ZOH uh» and are called scyphozoan jellyfish. Scyphozoan jellyfish are often seen at the coast and are sometimes called sea nettles. About the size of a soup bowl, they may be pale orange, pink, blue, or other colors.

Jellyfish swim by expanding the body like an opening umbrella, then pulling it together again rapidly. This squeezes water out from beneath the body and the jellyfish moves upward. When these movements stop, the jellyfish sinks to the ocean floor. On its way down, it catches small animals that touch its tentacles or oral arms. These parts contain stinging cells that explode when touched, driving tiny toxic (poisonous) threads into the victim and paralyzing it. The victim is then passed to the mouth of the jellyfish and swallowed.

The jellyfish body looks like a bell or umbrella. A short tube, which contains the mouth, hangs from the center of the body like a bell clapper. The edges of this tube form four frilly projections called oral arms. Another group of projections, called tentacles, hang down from the edges of the body. Each kind of jellyfish has a certain number and length of tentacles.

Over 200 different species, or types of jellyfish are found throughout the world's oceans and seas. These invertebrates, animals lacking backbones, belong to the phylum Cnidaria (ny-DARE-ee-uh). They come in many shapes and sizes, ranging from the tiny, spherical thimble jellyfish of the Caribbean to the largest jellyfish of them all, the Arctic lion's mane, whose tentacles may stretch over 100 feet in length. But what exactly are these creatures that are neither jelly nor fish? Is there anything else to them beyond their stinging reputation? The word "jellyfish" often brings to mind a white, gelatinous blob encountered on the beach, and many people react to jellyfish with instant fear. Although they do not resemble any other animals on earth, and appear quite bizarre, they are relatives of sea anemones and coral. Let's take a closer look at these beautiful and mysterious creatures so well suited to life in in the ocean.

Jellyfish can be found in all the world's oceans, and a few even inhabit freshwater. Over 95% water themselves, they have no heart, blood, brain, or gills.

The bell, or body of a jelly fish has one or more mouths on its central oral surface. Some jellyfish have frilly oral arms around the mouth. Jellyfish feed on small, drifting animals called zooplankton - which includes other jellyfish, juvenile fish and larval crustaceans. Tentacles, long string-like structures that surround the bell rim, trap food. These tentacles can be longer or shorter than the diameter of the jellyfish's bell.

Despite limited sense organs, jellyfish can smell, taste and remain balanced in the water. Special sacs, located on the bell rim, help jellyfish maintain balance. When a jellyfish shifts too far to one side or the other, the sacs stimulate nerve endings to contract muscles that re-orient the jellyfish in the correct direction (similar balance maintaining sacs are also found in the inner ear of humans). Jellyfish also have light sensing organs around the bell rim, and although jellyfish cannot detect objects, they can distinguish light from dark. Jellyfish can sense smells and tastes using chemoreceptors. Touch receptors on the tentacles, oral arms, and around the mouth sense movement and help jellyfish find food.

In addition to swimming, jellyfish are carried by wind, waves, and currents. They swim using jet propulsion. Special muscles, called coronal muscles, embedded on the underside of the bell push water out of the hollow bell. As water is pushed in one direction, the jellyfish moves in the opposite direction. While this may not seem to be very effective, one species of Mediterranean jellyfish that is only an inch and a half in diameter can move up and down the water column 3600 feet in one day; the equivalence of a 33 mile swim for a six foot tall person!

Some jellyfish, like the moon jellyfish develop in four distinct stages: the larval stage, the polyp stage, the ephyrae (e-FIE-ruh) stage, and the medusa stage. An adult female jellyfish produces eggs and holds them around her mouth. The male jellyfish then releases sperm into the water, and the female uses her oral arms and tentacles to bring in the sperm and fertilize her eggs. The eggs stay on the jellyfish's oral arms and grow into round, flat at larvae that are released into the water. The larvae are carried through the water until they find a hard surface which they attach to, such as a rock or a shell. After the larvae settle they develop into polyps, which resemble sea anemones.

Polyps usually develop over a period lasting a few months, but may live for several years producing clones, or exact copies of themselves during that time. At the end of this period polyps begin to form horizontal grooves that deepen through the body until the single polyp is transformed into a stack of individuals, much like a stack of pancakes. Flattened polyps enter the third stage of development as they break off the stack one by one and swim away. These young jellyfish (called ephyrae) now begin to resemble the familiar adult form called a medusa, as they develop tentacles and oral arms. A jellyfish in the medusa stage lives 2-6 months, usually perishing in rough waters.

Jellyfish are most known and avoided for stinging cells, located on the tentacles and other body parts. The stinging cell consists of a capsule with a sensory hair, a lid and an interior nematocyst, (nee-MAT-o-sist) which actually stings, captures and subdues prey. When the sensory hair is triggered by another animal's movements, the nematocyst fires from the capsule, much like a harpoon. A nematocyst fires in only a few milliseconds, making this cellular process one of the fastest in nature.