Lanx subrotunda. This limpet-shaped species evolved in the turbulent waters of large rivers in the western United States. Most other species of its family have shells with high, coiled spires. The streamlined shape of Lanx is an obvious advantage against getting swept away by strong currents.
John B. Burch (photographer; copyright holder), Mollusk Division, Museum of Zoology, University of Michigan-Ann Arbor
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