Jellyfish range in size from species that are no larger than a pea to an arctic jellyfish that may be about 7 feet in diameter. Jellyfish get their names from the jelly like material between the two layers of cells that make up the animal's body. This substance serves as a skeleton to support the fragile body wall and to help the jellyfish maintain balance in the water. The jellyfish body looks like a bell . 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. Jellyfish are classified as cnidarians, a phylum that includes corals, sea anemones, and hydras. Jellyfish swim by expanding the body like an opening umbrella, then pulling it together again and again. 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 threads into the victim and paralyzing it. The victim is then passed to the mouth of the jellyfish and swallowed. Some jellyfish can inflict painful and even deadly 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. Jellyfish produce their young from eggs. Each egg develops into a tiny polyp, a stage in which the animal looks like a hollow cylinder. The polyps attach themselves to the sea bottom. The jellyfish grow from the polyps by a process called budding. They are arranged on each polyp like a stack of saucers. The jellyfish, when they reach a certain size, detach from the polyp and develop into adult jellyfish. Jellyfish belong to the phylum Cnidaria. Large jellyfish make up the class Scyphozoa. Most small jellyfish belong to the class Hydrozoa.