This Identification Section was authored by:
Dr. S. Jerrine Nichols
U.S. Geological Survey
Great Lakes Research Center
1451 Green Road
Ann Arbor, MI 48105
Zebra mussels are not the only freshwater bivalve molluscs that are found in North America, nor are they the only introduced species. Because of this, it is important to be able to distinguish between zebra mussels and members of the other two bivalve superfamilies that occur in North American freshwater habitats.
Zebra mussels, Dreissena polymorpha, belong to the superfamily Dreissenacea. The quagga mussel, Dreissena bugensis, is the other introduced dreissenid bivalve in North America. D. bugensis and the native brackish water bivalve, the false dark mussel - Mytilopsis leucophaeata, are the two bivalves that are most likely to be confused with D. polymorpha.
If one examines the ventral shell margin and ventral shell edge of the mussels, differences are visible. Zebra mussels have a concave or flattened bottom and an acutely angled shell margin. Both features provide additional stability for the attached mussel. If one places representatives from all three species on a flat dish, the zebra mussel will be the only one able to stay upright. Both quagga mussels and Mytilopsis have a convex ventral edge and a rounded ventral or bottom margin.
The other North American bivalve superfamilies are the Unionacea and Corbiculacea (Burky 1983).
A wide variety of Unionacea can be found in North America.
The superfamily Corbiculacea contains two major families: the Corbiculidae and the Sphaeriidae.
The Corbiculidae were introduced to North America in the early 1900’s from Asia.
The Sphaeriidae are tiny clams that live in freshwater lakes, streams, rivers, ponds, and ephemeral habitats.
Unionid and sphaeroid species are native to North America and are easy to distinguish from the dreissenids or the Corbicula. The Corbiculidae were introduced to North America in the early 1900s and have also presented biofouling problems, but to a lesser extent than zebra mussels. Information is provided to aid in the identification and understanding of the three species of closely related bivalves (dreissenid) and members of the two remaining bivalve superfamilies - Unionacea and Corbiculacea.
The ability to detect and monitor present and future infestations of the zebra mussel is dependent upon the ability to separate the immature and adult stages from other similar native and introduced mussel species. While adult zebra mussels are fairly easy to separate from other mussel species, identification of the immatures is quite difficult. This CD includes two computer-based identification systems that will greatly reduce the learning curve associated with the identification of both the zebra and quagga mussel. For more information on identification of the zebra mussel, the quagga mussel, or the use of these systems, please click on the appropriate green/underlined topic heading listed below. Please note that users must access the computer-based identification system through the Information Manager.
Genetic Studies of the Zebra Mussel and the Discovery of the Quagga Mussel in North America