The Mussels of Nebraska

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Page 22 of 118

15 AWhile studying the Naiad-shells of the upper Ohio-drainage, the fact was forced upon my mind, that certain species which inhabit headwaters and smaller streams are represented, in the larger streams, by different, but very similar forms, which are distinguished from them chiefly by one character, namely obesity. The headwater-forms are rather compressed or flat, the large-river-forms more convex and swollen. I also found that in the rivers of medium size intergrades between the extremes are actually present.@ Often termed APlasticity@, this variability in shell shape led to each different form or shape being described and named as a new species. For instance, there are almost 80 different synonyms for the Eastern elliptio (Elliptio complanata). 29 The same thing was noted for the work done by Samuel Aughey in Nebraska in 1877 where he reported 83 taxa for Nebraska. Since then, 25 have since been combined and only 31 of the remaining 58 may have been accurately identified. 23 Well, so what? Well, please keep in mind that the shell you have in your hand may not exactly match the photos in a guidebook. I have observed this in Nebraska with the variability in the shells of the Giant floater. In the Salt Valley lakes around Lincoln, they are quite thin, glossy and a dark greenish brown. A little to the west, in the Big Blue River, the shells are thicker with a rough, brown/black exterior. Out west, in the southwest irrigation reservoirs, they have a moderately thick shell that is a glossy light tan with dark rings. So. . . look for the key identification characters and eliminate those that don't match. Then compare what is left and see if one fits. The Species Accounts The species accounts include a page summarizing biological information and a page of photographs A distribution map is included in the map section at the end of this guide. Photographs The photopage will attempt to include photos of an adult with exterior, interior and side views, a juvenile and an enlargement showing the beak sculpture. For most species I also cut a shell in half the long way and included a photo of this cross-section. The photographs illustrate the typical condition of shell found in Nebraska. That can vary from pristine to relict condition. For several species, live or fresh dead shell have never been

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