Clionidae

The Clionidae are a family of sea angels, which are a group of pelagic marine gastropods.

They resemble angels, complete with flapping "wings", hence their common name. They are gelatinous, mostly transparent pteropods, and they only have shells in their embryonic stage. They are mostly very small, with the largest species (Clione limacina) reaching 5 cm (2 in).