It's those magnificent Wingfoots again! Or "Pteropods" if you insist on being all fancy and, you know, accurate.
Pteropods are marine slugs and snails that have completely abandoned a life of slipping, sliding and sliming across the seabed. They bear two, squidgy wings which they use to swim through the sea like the marine equivalent of flying pigs. No wonder fish always look so astonished.
You can split Pteropods into two groups. Sea Butterflies are snails. They have a shell and are named after their lovely, fluttering style of swimming. The way they feed is less lovely and not at all like a butterfly. They produce a big mass of mucus which they dangle beneath like a snotty hot air balloon. Bits of food stick to it and once it's sufficiently laden, the Sea Butterfly eats the whole thing.
Then there are the Sea Angels. They're slugs, since they don't have a shell, and are named for their somewhat angelic appearance. They seem to have horns, though, which is less than angelic. And it only gets worse when they feed. Sea Angels are specialist hunters of Sea Butterflies and bear all manner of grotesque mouth parts for wrenching prey out of their shells. Yeah... "angels".
Slug Demons and Snot Balloons.
Wingfoots are so cool!