Oysters are bivalve mollusks characterized by having two unequal shells, one upper and one lower, which allow them to close hermetically to protect themselves. The shells can vary in size and shape, but are usually dark gray or brown in color. They are filter feeders that feed on plankton and other microorganisms present in the water.
They are one of the most appreciated seafood in gastronomy, and different varieties can be found depending on their origin and characteristics. Some of the best known species are the flat oyster and the Pacific oyster.