anterior adductor muscle

They also lack an anterior adductor muscle and do not secrete byssal threads, like mussels do.

The main muscular system in bivalves is the posterior and anterior adductor muscles, although the anterior muscles may be reduced or even lost in some species.

The interior of the shell is white with a broad pallial line, large anterior adductor muscle scar and smaller posterior adductor muscle scar.

In sedentary or recumbent bivalves that lie on one valve, such as the oysters and scallops, the anterior adductor muscle has been lost and the posterior muscle is positioned centrally.

However the placement of the umbo and anterior adductor muscle plus tooth size in the solitary fossil do not match H. minuta and thus Sánchez did not place the specimen into H. minuta.

The chalky buttercup can be distinguished by the fact that the interior of the valves are white rather than yellow and that the scars formed by the anterior adductor muscles slope at an angle of 30 to the pallial line.