Martin George/QVMAG

Jellyfish expert Lisa Gershwin caught this still unnamed species pictured here above some days ago while swimming near a jetty off the Australian island of Tasmania with a "phototank"—a small aquarium that makes it easy to photograph sea life.

To be precise this is not a proper jellyfish (a Cnidaria), but it belongs to the poorly known phylum Ctenophora. Although not closely related to cnidarian jellyfish, ctenophores are also free-swimming planktonic carnivores, are also generally transparent or translucent, and occur in shallow to deep portions of all the world's oceans. Ctenophores move using eight rows of fused cilia that beat in metachronal waves that diffract light, so that they sparkle with all of the colors of the rainbow. So the wonderful colours you see are not directly emitted by the animal as in many other deep abyss species but rather it's reflected light.

Another aspect of this Rainbow Jellyfish that I find amazing is its incredible fragility:
"It shatters as soon as it touches a net" said Lisa Gershwin

Further info at National Geographic

In the following videos you can see some other Ctenophores and their incredible rainbow glowing: