Pteropods are pelagic snails; this is Cavolinia gibbosa, a thecosome in the family Cavoliniidae. They live in the water column and retain shells, like their terrestrial cousins. Parapodia are used for swimming, and extend from the shell of the animal. This individual trawled from between 1,500 meters depth and the surface, Gulf of Mexico, 2016. Image courtesy of the DEEPEND project.