Oysters

A zig zag oyster - one of the distinctive molluscs on the Great Barrier Reef

Oysters belong to the group of molluscs known as Bivalves, which also includes mussels, clams, scallops and shipworms.

Unlike snails, the bivalves have no head and no radula - the raspy tongue snails use to scrape up their food. The name 'bivalve' literally means twin doors - a reference to the two shells that provide them with protection from predators.

Feeding

Like clams, oysters are sedentary filter feeders that depend on currents created by cilia in their gills to provide them with food from the surrounding water.

Habitat

Oysters attach their shells to a surface by secreting cement - literally glueing themselves to the sea bed.

Pearls of Wisdom

Oysters and clams cover irritants, such as grains of sand that get under their shells, with layers of Calcium carbonate, eventually forming pearls.

The largest pearl ever found came from a giant clam in the Philippines. It weighs more than six kilograms, looks like a human brain, and is called the Pearl of Lao-tze.