The flat oyster is oval, almost circular shaped. The shell is almost flat on one side and the other side is deeply cupped. The flat side is usually attached to hard substrata. The shell has circular radiating ridges on the outside, the inside is smooth. The oysters reproduce between May and August, by releasing larvae that will live pelagic for about two weeks. In the sixties this species almost became extinct, after a disease and a cold winter. Because oyster were being cultivated and had an important commercial value, it was decided to import Crassostrea gigas until the native flat oyster had recovered. Currently Crassostrea gigas has removed the flat oyster almost completly in Zeeland.

About 150 mm in diameter.

The outside is grey-brown to blue-brown. The inside is white to grey-white.

From the shallows up to a depth of 50 metres.

North Eastern Atlantic from Norway till the Mediterranean and Black sea.