A Key to the Freshwater Mussels (Bivalvia: Unionidae) of the Hudson Bay and Lake Superior Drainages of Northern Minnesota, North Dakota, and Canada by Daniel L. Graf Department of Biology & Museum of Zoology University of Michigan, Ann Arbor MI 48109 Updated 20 July, 2000.

With the exception of the Red River of the North and its tributaries (e.g., Cvancara, 1970), the Nelson River and Lake Superior basins of northern Minnesota have been largely unstudied with respect to their freshwater mussel (Bivalvia: Unionidae) faunas (reviewed in Graf, 1997a, 1997b). While several extensive keys and handbooks are available that include the Minnesota or adjoining regions (e.g., Baker, 1928; Dawley, 1944; Burch, 1975; Eddy et al., 1982; Oesch, 1984; Cummings and Mayer, 1992), they were designed to deal with the unionid fauna of the Mississippi basin and are therefore cumbersome when dealing with these northern basins. In an effort to facilitate the study of Nelson River and Lake Superior mussels in Minnesota and North Dakota a concise key to their identification follows.

1. Pseudocardinal and lateral teeth absent. 2

Pseudocardinal and/or lateral teeth present. 5

2 (1). Umbo sculpturing double-looped. 3

Umbo sculpturing not double-looped. 4

3 (2). Umbos not extending above the hinge-line; shell small and thin, generally without rays. Utterbackia imbecillis (Say) U. imbecillis has only been confirmed from the Lake Superior Drainage (Graf & Underhill, 1997). It has recently been reported from the Lake of the Woods watershed (Hove et al., 1997).

Umbos broad and extending above the hinge-line; shell from small to large and moderately thin. Pyganodon grandis (Say) P. grandis occurs in the Red River, Lake of the Woods, and Lake Superior basins (Graf, 1997a)

4 (2). Umbo sculpturing course with a sharp posterior angle; hinge-line conspicuously thickened anterior to the umbo in the right valve and directly below the umbo in the left; shell small to medium-sized; periostracum dark; nacre often salmon colored. Strophitus undulatus (Say) S. undulatus occurs in the Red River and Lake of the Woods basins (Graf, 1997a), but it has not been reported from the Lake Superior Basin (Graf & Underhill, 1997).

Umbonal sculpturing fine with a shap posterior angle; posterior ridge wide and inflated; shell generally small and thin. Anodontoidea ferussacianus (Lea) A. ferussacianus occurs in the Red River, Lake of the Woods, and Lake Superior basins (Graf, 1997a).

5 (1). Shell laterally compressed; umbobal sculpturing strongly double-looped; lateral and/or pseudocardinal teeth generally poorly-developed. 6

Umbonal sculpturing not or only weakly double-looped; lateral and pseudocardinal teeth well-developed. 8

6 (5). Shell without flutings between the posterior ridge and posterior margin. 7

Shell with flutings between the posterior ridge and posterior margin; lateral teeth developed only as thickenings of the hinge-line. Lasmigona costata (Rafinesque) L. costata has only been confirmed from the Red River of the North (Graf, 1997a), but it has recently been reported from the Lake of the Woods drainage (Hove et al., 1997).

7 (6). Shell alate and often large; pseudocardinal teeth well-developed, lateral teeth developed only as thinkening of the hinge-line; nacre white. Lasmigona complanata (Barnes) L. complanata occurs in the Red River, Lake of the Woods, and Lake Superior basins (Graf, 1997a). [picture]

Shell not alate and small to medium-sized; lateral teeth often well-developed, delicate, and double in both valves; pseudocardinals present as a projection directly below the left umbo; nacre often tinged with salmon. Lasmigona compressa (Lea) L. compressa occurs in the Red River, Lake of the Woods, and Lake Superior basins (Graf, 1997a).

8 (5). Shell without knobs or pustules. 9

Shells with a row of raised knobs on each side of a wide sulcus. Quadrula quadrula (Rafinesque) Q. quadrula is found only in the Red River drainage (Graf, 1997a).

9 (8). Shell elongate, generally twice as long as it is high; nacre often pink or purple; periostracum dark, sometimes with green rays. 10

Shell not twice as long as high; if nacre is pink, the shell is laterally compressed and alate; otherwise, the periostracum is brown to yellow, sometimes with green rays. 11

10 (9). Nacre often pink to purple, sometimes white; periostracum generally dark but with rays; shell often largel posterior margin bluntly pointed with dorso-posterior margin extending further than the ventro-posterior margin. Ligumia recta (Lamarck) L. recta inhabits the Red River, Lake of the Woods, and Lake Superior drainages (Graf, 1997a).

Nacre purple to lavender, often white; periostracum dark; posterior margin extending further than the dorso-posterior margin. Elliptio complanata (Lightfoot) E. complanata is found only in Lake Superior (Graf & Underhill, 1997).

11 (9). Shell not alate; nacre generally white to salmon; periostracum brown to yellow, sometimes with green rays. 12

Shell alate and laterally compressed, usually with pink nacre. Potamilus alatus (Rafinesque) P. alatus has only been reported from the Red River of the North and tributaries (Graf, 1997a).

12 (11). Lateral teeth parallel to or nearly parallel with the ventral margin; periostracum light brown-orange to yellow, often with green rays. 13

Lateral teeth not parallel with the ventral margin; periostracum generall brown to yellow and lacking rays; often with a broad, shallow sulcus anterior to the posterior ridge. Fusconaia flava (Rafinesque) F. flava has been repored from only the Red River drainage (Graf, 1997a).

13 (12). Dorsal and ventral margins straight; shell drawn out posteriorly with the posterior end either square and inflated (females) or bluntly pointed (males); umbo sculpturing composed of numerous fine, wavy ridges. Lampsilis siliquoidea (Barnes) L. siliquoidea occurs in the Red River, Lake of the Woods, and Lake Superior basins (Graf, 1997a).

Ventral margin slightly rounded; shell generally inflated and more square (females) or ovate (males) than the previous species; beak sculpture composed of a few weakly double-looped ridges. Lampsilis cardium (Rafinesque) L. cardium occurs in the Red River, Lake of the Woods, and Lake Superior basins (Graf, 1997a).

References Cited Baker, F.C. 1928. The fresh water Mollusca of Wisconsin: Part II. Pelecypoda. Bulletin of the Wisconsin Geological and Natural History Survey, vol. 70, No. 2. University of Wisconsin. 495 pp. Burch, J.B. 1975. Freshwater Unionacean Clams (Mollusca: Pelecypoda) of North America. Malacological Publications. xviii + 204 pp. Cummings, K.S., C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey Manual 5. Champaign, Illinois. xiii + 194 pp. Cvancara, A.M. 1970. Mussels (Unionidae) of the Red River Valley in North Dakota and Minnesota. Malacologia 10: 57-90. Dawley, C.W. 1944. Distribution and growth studies of the Unionidae and aquatic Gastropoda found in Minnesota. Ph.D. Thesis, University of Minnesota. 307 pp. Eddy, S., A.C. Hodson, J.C. Underhill, W.D. Schmid, D.E. Gibson. 1982. Taxonomic Keys to the Common Animals of the North Central States, Exclusive of the Parasitic Worms, Terrestrial Insects, and Birds, 4th Edition. Burgess Publishing, Minneapolis, Minnesota. vi + 205 pp. Graf, D.L. 1997a. Distribution of unionoid (Bivalvia) faunas in Minnesota, USA. Nautilus 110: 45-54. Graf, D.L. 1997b. Northern redistribution of freshwater pearly mussels (Bivalvia: Unionoidea) during Wisconsin deglaciation in the southern Glacial Lake Agassiz region: a review. American Midland Naturalist 138: 37-47. Graf, D.L., J.C. Underhill. 1997. The western Lake Superior freshwater mussel (Bivalvia: Unionidae) community and its origin. Occasional Papers on Mollusks 5(74): 409-417. Hove, M. S. Strong, A. Jaconson, J. Schussler, V. Kurth. 1997. Northern Minnesota river holds three state-listed mussels. Triannual Unionid Report (13): 22. Oesch, R.D. 1984. Missouri Naiades: a Guide to the Mussels of Missouri. Missouri Department of Conservation, Jefferson City, Missouri. viii + 271 pp.