A flat, roughly circular oyster with a straight hinge line and a shell built in overlapping layers rather than solid folds. The outside is dark green to black with pale radial rays and rows of flattened scales along the growth edges; the inside is thick, brilliant nacre, ringed by the dark band around the margin that gives the species both its English name and margaritifera, pearl-bearing. Width reaches about 30 cm (12 in), though most animals on the reef are half that. A tuft of byssal threads anchors it, so it can be detached without breaking the shell.
It attaches to coral rock, drop-offs, lagoon patch reefs and wreck structure between about 1 and 40 m (3 and 130 ft), usually singly and often tucked into a crevice with only the gape showing. Feeding is by filtration. Pearls form when a foreign particle lodges in the mantle and is walled off in nacre, and this species supported the historic 🌊 Red Sea pearl fishery centered on the Dahlak Archipelago and the Farasan Islands - a trade that ran for centuries before cultured pearls ended it in the twentieth century.
- flat, rounded shell with a straight hinge line
- dark green-black exterior with pale radial rays
- interior brilliant nacre, dark band around the margin
