Aurelia aurita (also called the common jellyfish, moon jellyfish, moon jelly or saucer jelly) is a species of the family Ulmaridae. All species in the genus are very similar, and it is difficult to identify Aurelia medusae without genetic sampling; most of what follows applies equally to all species of the genus.

The jellyfish is almost entirely translucent, usually about 25–40 cm (10–16 in) in diameter, and can be recognized by its four horseshoe-shaped gonads, easily seen through the top of the bell. It feeds by collecting medusae, plankton, and mollusks with its tentacles, and bringing them into its body for digestion. It is capable of only limited motion, and drifts with the current, even when swimming.

The moon jelly differs from many jellyfish in that they lack long, potent stinging tentacles. Instead they have hundreds of short, fine tentacles that line the bell margin. The sting has a mild effect on humans, with most having little or no reaction.

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