1) Family ostreidae 2) Mollusk family 3) Oysters 
The Ostreidae, the true oysters, include most species of molluscs commonly consumed as oysters. Pearl oysters are not true oysters, and belong to the order Pterioida. Like scallops, true oysters have a central adductor muscle, which means the shell has a characteristic central scar marking its point of attachment. The shell tends to be irregular a...
(from the article `bivalve`) ...close attachment of one valve to a hard surface, and although some groups still retain byssal attachment (family Anomiidae), others have forsaken ...
[n] - oysters
family Ostreidae noun oysters