In the world's oceans, billions of tiny marine snails (a form of plankton) commute daily between surface waters, where they feed at night, to depths of several hundred meters during the day to rest while avoiding predators. Marine snails play an important role in geochemical cycles and climate: 12-13% of the global carbonate flux occurs when the calcium carbonate shells of dead snails sink to the depths, where they dissolve and contribute to atmospheric carbon and ocean acidification. But because they are difficult to study and can't be kept in the laboratory, the behavior of these animals—which bear poetic names such as sea butterflies—is poorly known, especially for the subtropical and tropical regions where their diversity is greatest.