Sea angels (scientific name Gymnosomata) are actually sea slugs. The sea angel is actually translucent and shell-less. It does not grow more than 5 cm in length. The projections found on top of the angel's head are actually its sensory organs. Its feet have even evolved into wing-like appendages called the parapodia. So remember, it's not arms or wings that a sea angel flaps, but instead its feet!