Pinctada maxima is a species of pearl oyster, a marine bivalve mollusk in the family Pteriidae, the pearl oysters. There are two different color varieties: the Gold-lipped oyster and the Silver-lipped oyster. These bivalves are the largest pearl oysters in the world. They have a very strong inner shell layer composed of nacre, also known as "mother of pearl" and are important to the cultured pearl industry as they are cultivated to produce South Sea pearls.
The South Sea pearl or Philippine pearl was declared by Philippine President Fidel Ramos as the national gem in 1996 through Proclamation No. 905. The oyster and pearl are depicted on the reverse side of the Philippine New Generation Currency Series 1,000-peso bill.