Physella gyrina. The light band (varix) on the shell shown here was caused by the snail's much slower growth during the winter. While the shell growth was slower at the varix, a thicker shell was produced at this site (which masks the dark mantle [skin covering the viscera] of the snail's body, that elsewhere shows through the translucent shell).
John B. Burch (photographer; copyright holder), Mollusk Division, Museum of Zoology, University of Michigan-Ann Arbor
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