With colorful translucent wings and traveling with such grace, to be labeled a swimming sea slug, or Gymnosomata, seems wrong. It even has devil horns on its little head but no matter, it gets to be referred to as a "sea angel."
But they catch their prey by shooting tentacles out of their face then they rip the prey out of its shell, swallowing it whole. Doesn't that deserve a more sinister title? Nope. "Angel" because of aforementioned pretty rainbow wings that Pixar, I mean, nature, created for the icy Russian seas.