Jellyfish are sea creatures with bell-shaped, jelly-like bodies, and long stinging tentacles.
Biologists call jellyfish medusa, after the mythical Greek goddess Medusa, who had wriggling snakes for hair.
Jellyfish belong to a large group of sea creatures called cnidarians, which also includes corals and anemones.
Unlike anemones, jellyfish float about freely, moving by squeezing water out from beneath their body. When a jellyfish stops squeezing, it slowly sinks.
A jellyfish’s tentacles are covered with stinging cells called nematocysts, which are used to catch fish and for protection. The stinging cells explode when touched, driving tiny poisonous threads into the victim.
Jellyfish vary in size from a few millimetres to over 2 m.
The bell of one giant jellyfish measured 2.29 m across. Its tentacles were over 36 m long.
The Portuguese man-of-war is not a true jellyfish, but a collection of hundreds of tiny animals called polyps which live together under a gas-filled float.
The purple jellyfish can be red, yellow or purple.
Jellyfish are among the world’s most ancient animals.