The jellyfish is an unusual sea creature. Soft-bodied & lacking a skeleton, it has none of the features of a fish. More than nine tenths of its body is like jelly.
Jellyfish are found in all oceans, & some disk-shaped ones can be seen along the shoreline. Certain species are found mainly in tropical & subtropical seas. Others prefer cooler waters. Most jellyfish live at or near the surface of the sea, though some dwell on the bottom.
Jellyfish range in size from 1 inch to more than 6 feet (2 centimeters to 2 meters) in diameter. Their bodies are made up almost entirely of water. A typical jellyfish is umbrella-shaped; it may have a few or many tentacles. It swims with the help of simple muscles on its underside. A network of nerves controls these muscles, which contract like the closing of an umbrella. The tentacles, lined with stinging cells, are capable of stunning small animals. Some jellyfish have simple eyes located along the edge of the body. Jellyfish may be transparent, white, brown, pink, or blue. Some deep-sea jellyfish are maroon.
Most jellyfish feed on small animals that are trapped by the tentacles & drawn into the mouth. Other types of jellyfish get food simply by filtering tiny animals & plants from the surrounding water.
The formation of a new jellyfish begins with an egg. A larva hatches from the egg & swims about for a short time. Then it settles at the sea bottom & develops a body, a mouth, & tentacles. This structure develops into segments that look like a pile of saucers. Some of the segments remain attached to the structure. Others break away & become jellyfish. Jellyfish can live from only a few weeks to a year or longer.
Jellyfish are known to sting swimmers who accidently brush up against them in the water. Although these stings are painful, they are usually not deadly. However, even dead jellyfish that are washed up on the beach can be harmful & should never be touched.
Some jellyfish, called sea wasps, are very dangerous to humans. They inject their prey with a poison more harmful than any snake venom. Even a moderate sting from a sea wasp can cause death within a few minutes. Sea wasps live near the coasts of Japan & northern Australia.
