Family Ostreidae

Shell size to 50 mm; shell outline ovate, otherwise very variable. Edge of lower valve raised and crenulated. Edge of upper valve with fine denticles. Muscle scar central. Color gray, sometimes with greenish tinges. Interior of shell nacreous, grayish to greenish. Ostrea stentina Payraudeau, 1826 is restricted to the eastern Atlantic.

Shell size to 45 mm; shell outline variable: usually elongate when attached to sea whips; rounded when living on rocks or other hard substrates. Sometimes with central ridge and branching ribs. Claw-like projections on these ribs serve to attach the bivalve onto the stem of a sea whip. Inner margins with tiny, pimple-like denticles. Color reddish- to dark-brown.

Shell size to 150 mm; shell thick and heavy, usually narrow and elongate, but extremely variable in shape. Upper valve flatter, smaller than lower valve; lower valve convex. Shell outline variable. Shell margins usually undulating. Umbones long and curved. Color dirty- to light-gray, sometimes striped or flecked with brown, internally white with muscle scar deep purple. Lives attached to mangrove roots, rocks, other oyster shells. Species represent the northern counterpart of Crassostrea rhizophorae.