Pinctada margaritifera, commonly known as the black-lip pearl oyster, is a species of pearl oyster, a saltwater mollusk, a marinebivalvemollusk in the family Pteriidae. This species is common in the Indo-Pacific within tropical coral reefs.
The ability of P. margaritifera to produce pearls means that the species is a valuable resource to humans. The oysters are harvested wild from coral reefs and are also commonly grown in aquaculture, both primarily taking place in the Indo-Pacific region.
Description
Internal appearance of shell
The common name of this species refers to the black coloring along the margins of the interior of the shell. Externally the shell is dark grayish brown or green, though white spots are common across the shell. Adults usually reach between 20 and 25 centimetres (7.9 and 9.8 in) in height. A distinctive feature of the species is that the hinge has no teeth.
(The genera Pinctada and Pteria are often confused. In Pinctada, the hinge is long and straight, the long end of the shell forms a right angle to the hinge, and the left valve is slightly deeper than the right. In the genus Pteria, the shell width is much longer than its height and the angle of the hinge is prominent and pronounced.)
This species is commonly farmed and harvested for pearls, and there is general consensus that the quality of pearls from Pinctada margaritifera is the highest quality out of all the pearl oysters. Pearls form when a parasite or other irritant enters into the oyster and nacre is released by the oyster to coat the object, eventually creating a small pearl. It is a popular myth that sand is a common irritant that induces pearl nucleation, however, this is very rarely, if ever, the case. Bivalves are able to flush sand from their bodies extremely effectively, and studies of pearl nuclei have shown that the overwhelming majority form from parasitic incursion, other organic irritants, or even tissue damage. The oyster's release of the nacre serves as an adaptation of the immune system to isolate the invasive particle and irritation. P. margaritifera in particular produces gray or black pearls.
The benthic ecology of the region is a significant factor in the rate of production and the quality of pearls. Rocky, gravelly bottoms and low silt concentrations are preferable, and currents are necessary to keep the water clean with fresh phytoplankton and removal of fecal matter. Stronger currents cause faster but lower quality pearl development.
