Jellyfish Facts

About the jellyfish

The bell is made of a jelly-like substance called mesoglea, and it squeezes rhythmically to push the animal through open water. Tentacles hanging underneath catch prey and fend off predators. A few kinds stay anchored to the seabed by stalks. Jellyfish turn up everywhere, from the surface to the deep sea, and big, colorful ones are common along coasts. True jellyfish live only in the sea, though some look-alike hydrozoans live in fresh water.

Their life cycle has two acts. The medusa, the familiar floating form, is usually the sexual stage and releases larvae that drift off and settle as polyps on the seabed. Medusae often grow fast, mature within a few months and die soon after breeding, while polyps may live much longer. Jellyfish have existed for at least 500 million years, possibly 700 million or more.

Did you know?

• Jellyfish are the oldest group of animals with multiple organs.
• In some Asian countries, salted and pressed jellyfish are eaten as a delicacy.
• Other names for jellyfish include sea jellies and simply jellies.