Pearl Oyster

pearl oyster the common name of Pinctada maxima and P. margaritifera, edible bivalves of SE Asia. They are not true oysters, but there is a general resemblance. P. maxima may measure 30 cm (1') and has shells which are at first yellow but later purplish-black. The inside is of a pearly brilliance; and there may be an actual pearl inside as well. P. margaritifera is dark inside.