Atolla wyvillei, also known as Atolla jellyfish or Coronate medusa, is a species of deep-sea crown jellyfish (Scyphozoa: Coronatae). It lives in oceans around the world. Like many species of mid-water animals, it is deep red in color. This species was named in honor of Sir Charles Wyville Thomson, chief scientist on the Challenger expedition.
It typically has 20 marginal tentacles and one hypertrophied tentacle which is larger than the rest. This long trailing tentacle is thought to facilitate prey capture.
This species is bioluminescent. When attacked, it will launch a series of flashes, whose function is to draw predators who will be more interested in the attacker than itself. This has earned the animal the nickname “alarm jellyfish”. source