Pearl oyster

The black-lip pearl oyster (Pinctada margaritifera) is a large saltwater shellfish that lives on tropical coral reefs. Its shell is dark grey-brown or green on the outside, often with white spots, and shiny mother-of-pearl on the inside. Adults are usually about 20 to 25 centimetres tall.

It is common across the Indo-Pacific and is best known for making pearls, including the famous Tahitian black pearls. People harvest it in the wild and also raise it on farms. The Persian Gulf, here shown near Bahrain, has long been famous for pearl diving. The name 'black-lip' comes from the dark colour around the edge of the shell's inner surface.

How a pearl forms

A pearl begins when something irritating gets inside the oyster, such as a parasite or a tiny particle. To protect itself, the oyster covers the object with thin layers of shiny nacre, the same material that lines its shell. Over time, a small pearl grows. It is a popular myth that a grain of sand is the usual cause. The pearls of this species are generally considered the highest-quality pearls of all the pearl oysters.

Life on the reef

The oyster attaches itself to rocks, coral and barnacles with strong threads called a byssus. It lives from the low-tide line down to about 75 metres, in clear water with few nutrients, and it feeds by filtering tiny particles from the water. Its range stretches from the Red Sea and Persian Gulf to French Polynesia, Australia, Japan and the coasts of India. Many other animals, including sponges, worms and fish, live around pearl oyster beds.

On the globe

The model shows a black-lip pearl oyster in the Persian Gulf near Bahrain. Look for its rough outer shell and shiny mother-of-pearl inside.