Hermes of Snails
The Sea Butterfly is just as pretty as it is confusing to look at. They're all in the suborder Thecosomata, a group of wing-footed snails that float at the edge of light eating plankton. Most of them have thin shells, clear bodies, and a large and beautiful adapted foot that forms two "wings." Compared to land snails, these guys are upside down with their stomach facing upwards and their shell hanging down.
They float with plankton along ocean currents hanging below the sunlight zone during day and rising at night for better feeding. To feed, they cast out mucus like a spider's web around themselves. When they feel like enough plankton has gotten trapped, it'll reel it all back in, reusing to mucus for another trap.
They're eaten by just about anything. Their role in the ecosystem is to make the energy found in plankton and debris available for larger creatures. One notable predator of theirs is evolved to eat them almost exclusively, another sea snail with wings that's totally different. You can read about Sea Angels here.
Their role so low on the food chain becomes much more important in extreme ecosystems like the arctic where these guys are prevalent. Because they are such thin shelled creatures, their bodies are easily damaged by ocean acidification. Acidification is the increase of dissolved CO2 in the water, creating Carbonic Acid. The acid binds with the calcium in shelled creatures and leeches it out of their bodies, destroying their integrity. Cold water can hold much more dissolved carbonic acid than warm water, an effect you might have noticed with soda or beer. As much as coral bleaching affects the tropics, shell degredation disrupts our arctic food chains.
As far as rating them goes, they're very pretty and I like their method of eating. However, they're almost just plankton. It feels a little irresponsible given that I just made a bleeding heart ecological plea for them, but they aren't getting a great score. Their biggest op gets called by their same name sometimes!