Sea butterflies’ shells determine how the snails swim
Sea butterflies flit through the ocean on gossamer wings, each species with a style of its own. These tiny marine snails, or thecosomes, migrate up to surface waters at night to feed and sink to deeper waters during the day to hide from predators. But exactly how they move through the water has remained a mystery, as these delicate creatures survive only a couple days in captivity. New videos of sea butterflies in an aquarium reveal that snail species swim and sink at different angles and speeds, depending on the sizes and shapes of their shells, researchers report online September 7 in Frontiers in Marine Science. The finding could help biologists better understand marine snail migration, and inspire new designs for underwater robots (SN: 1/3/18). Mechanical engineer David Murphy of the University of South Florida in Tampa and colleagues videotaped seven species of sea butterflies collected off Bermuda. The catch included two tiny...