I'd be surprised if anyone can guess this without scrolling down to see the full version, and even then it'd be tough.
Hints? If you are a biologist, you'll have a good shot at it. If you're a marine biologist, you have no excuse for not knowing, I guess.
The image shows light refracting off a comb jelly (don't call it a jellyfish). See the whole thing below.
Comb jellies have connective tissues and a nervous system, and though they have tentacles and are all squishy, they are not really true jellyfish. In 2008, scientists discovered evidence indicating comb jellies were the first animals (sponges had previously laid claim to that title).
Comb jellies are one of many fascinating species lurking in the enigmatic deep sea, as discussed in this new feature article about the vast and deep mysteries of the ocean over on our sister site, OurAmazingPlanet.