Largest pearl oyster

The world's largest species of pearl oyster is the South Sea or Philippine pearl oyster Pinctada maxima, which grows up to 30 cm in diameter, i.e., roughly the size of a dinner plate. It exists in two different intraspecific colour varieties – the white-lipped and the gold-lipped, being distinguished from one another by the colour of the outer edge of their shell's interior. They also produce a range of different coloured pearls, including white, silver, champagne and gold. This species is native to the seas around the Philippines (where its pearl is officially recognized as that country's national gem), as well as Indonesia, Australia and Fiji, usually at a depth of 5–30 m, but sometimes as deep as 60 m.

Pearl oysters belong to an entirely separate taxonomic order – Pterioida, the feathered oysters – from that of true oysters, which are housed in the order Ostreoida. The latter includes the edible oysters, which can occasionally produce pearls but they are invariably small and of very poor quality.

Other molluscs loosely referred to as oysters are the thorny oysters (more closely related to scallops) and the saddle oysters (certain saltwater clams).