Article | Updated 7 years ago

Clay Bryce, courtesy WA Museum
Encrusted Pinctada maxima pearlshell situated in a ‘garden bottom’ of sponges, corals and bedrock.
Image of an underwater scene

Pinctada species are bivalves of great beauty and great age. These shells, with their mother-of-pearl interiors, belong to the Mollusca, the most diverse marine phylum on earth. The group is ancient, with a fossil record dating back almost 550 million years. They are related to well-known groups such as gastropods (snails), cephalopods (octopus), scaphopods (tusk shells) and other bivalves (clams, edible oysters and mussels).

Australia is home to nine species of Pinctada, four of which are found in the tropical coastal waters of northern Australia – Pinctada maxima, Pinctada albina, Pinctada imbricata fucata, Pinctada margaritifera – often in prolific quantities. Pinctada maxima is one of the most sought-after species; these bivalves have enormous shells, with very white and thick nacre, and produce some of the largest and most lustrous pearls in the world.

Image of an underwater scene

Encrusted Pinctada maxima pearlshell situated in a ‘garden bottom’ of sponges, corals and bedrock.
Image copyright WA Museum 

Pinctada Family Tree

KINGDOM       Animalia

PHYLUM         Mollusca

CLASS            Bivalvia

ORDER           Pterioida

FAMILY          Pteriidae

GENUS           Pinctada

SPECIES        Various (four species found in northern Australian waters: P. maxima, P. albina, P. imbricata fucata, P. margaritifera)

Pinctada maxima pearl oysters are often referred to simply as MOP (mother of pearl). They occur in two different varieties: the white or silver-lipped oyster and the gold-lipped oyster. This species is common in the coastal waters of northern Australia, which has led to it being collected in abundant quantities. Relatively impervious to changes in temperature and humidity, P. maxima is attractive and can readily be carved. These oysters are renowned as the source of the ‘South Sea Pearls’.

As the name would suggest, adult P. maxima are the largest pearl oysters in the world. The largest individual specimen ever recorded, which was found in the Torres Strait, measured 250 x 282 millimetres.

3D Structure

The genus Pinctada was formally named by the German naturalist Peter Friedrich Röding in 1798. There are many different species of Pinctada, and recent genetic studies of pearlshell DNA are now challenging older versions of the Pinctada classification.