Pearl Oysters

the common name for marine and fresh-water bivalve mollusks in whose mantles pearls can form. Marine oysters of the genus Pinctada, with round shells, live in tropical waters and are harvested for their pearls. In Japan they are raised. Freshwater oysters of the species P. margaritifera, with kidney-shaped shells, live in temperate climates in rivers with pure, clear water. The insides of oyster shells are covered with a thick layer of mother-of-pearl, which is used to make buttons and other articles.