On the lateral margin of the myophore plate in Mytilopsisleucophaeata is a small projection or apophysis. It is absent in zebra and quagga mussels.
All three dreissenid mussels have a shelf or myophore plate located anteriorly on the internal portion of the shell. Only Mytilopsis leucophaeata has an apophysis or projection on the lateral margin of its myophore plate (as indicated by an arrow). This protrusion, used for muscle attachment, is absent in both zebra and quagga mussels. It can be observed using a good hand lens or dissecting microscope.
For further information, see Myophore Plate.
Adult Identification Information
Zebra Mussel Identification