Red Medusa Jellyfish (Atolla wyvillei)
The jellyfish Atolla lives worldwide in the deep sea, where light levels are very low. The jellyfish is bioluminescent—emitting blue-green light—and so are most of its prey. Scientists think that the deep red color of the animal’s stomach serves a purpose—to keep the blue light of its luminescent lunch from escaping and giving away Atolla’s location to its own predators. It is distinguished by a larger size (up to 15 cm), 8 oval-shaped gonads in pairs, more tentacles (usually 22, but ranging from 20 to 36), and more uniform red coloration of the bell (although some individuals may lack this pigmentation.)

