Oysters for sale, snack time, at a market in London.
The common name oyster is used for a number of different groups of bivalve mollusks, most of which live in marine or brackish water. The shell consists of two usually highly calcified valves which surround a soft body. Gills filter plankton from the water, and strong adductor muscles are used to hold the shell closed.
The oyster is used as a metaphor in an idiomatic saying, "The world is your oyster", which means that the whole world is laid out before you like a wonderful living buffet