Oysters are bivalves, meaning their soft bodies are encased in hinged shells. They are also filter feeders, a diverse group of animals that includes sponges, flamingos, and baleen whales. These creatures eat by pulling water through their bodies and across specialized feeding organs—and then pushing out the leftovers.
Wrapped within an oyster’s tough shell are delicate layered gills used for breathing and feeding. Miniscule hairlike structures called cilia line these gills and guide plankton and algae into the mollusk’s mouth. They also catch other gunk dirtying the water column, like nitrogen, sediment, and even metals.