Ostreoidea is a
taxonomic superfamily of
bivalve marine
mollusc, sometimes simply identified as
oysters, containing two families. The ostreoids are characterized in part by the presence of a well developed axial rod. Anal flaps are known to exist within the family
Ostreidae but not within the more-primitive
Gryphaeidae. The scar from the adductor muscle is simple, with a single, central scar. In the majority, the right
valve is less convex than the left.