You may look for pearls in a plate of oysters on the half shell, but you won't find the type of pearl used to make jewellery in your meal. Pearl-producing oysters -- the kind that make fine, round pearls -- are large and inedible. Edible varieties of oysters are small, tender and harvested all over the world.
The Virginica, or Eastern, oyster is found primarily along the North American coastline from northern Canada to the Gulf of Mexico. Also known by the species name Crassostrea virginica they are commonly found off of New York, Massachusetts, Maryland, Florida and Louisiana, and have many different regional names including Bluefleet, Box and Breton Sound. These oysters are best eaten raw, especially those harvested farther north.
The Pacific oyster is native to Japan and was imported to North American waters to replenish the depleted oyster population off the West Coast in the 1920s. Pacific oysters are now cultivated locally in North America and Europe. Larger Pacific oysters, while edible, are rarely eaten raw. Smaller types, such as the Totten and the Mad River, are commonly served raw on the half shell. The Pacific oyster is also known by its species name Crassostrea gigas.
The European oyster is small, expensive and popular in France, Great Britain and the United States. European oysters, which have the species name Ostrea edulis, are always served raw. They are also known as Belon, Dorset or flat oysters.
The Portuguese oyster, or Crassostrea angulata, is native to Portugal and Spain. The Portuguese oyster has been largely replaced with the Pacific oyster in Europe due a dramatic population reduction in the late 1960s and early 1970s. Portuguese oysters are usually served cooked rather than raw.
The Olympia oyster was once the primary oyster of the North American West Coast. Due to over-harvesting, the Olympia oyster, also known as Ostrea lurida, nearly became extinct and has been largely replaced by the Pacific oyster in North America. Olympia oysters are tiny and flavourful, and usually served raw.