Aurelia aurita, popularly known as the moon jellyfish, is a widely studied species of the genus Aurelia. It is 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. Capable of only limited motion, it drifts with the current, even when swimming.Photograph: Alexander Vasenin