Smooth Periwinkle (Littorina obtusata) is a small mollusk of the New England coastline who lives in association with Knotted Wrack, Bladder Wrack, and other types of marine algae. Smooth Periwinkle's nearly flat spire is distinctive among local periwinkles. Most of the individuals I've noticed have been yellow (another common name for this species is Northern Yellow Periwinkle), but shell color is variable, and may instead be red, brown, green, or multi-colored. To learn more about this mollusk, check out this species ID card offered by the Gulf of Maine Research Institute.
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