Species of the Week

Periwinkles (Littorina spp.)

Illustration from "Discover Nature at the Seashore", Lawlor 1992

We have 3 species of periwinkle in our area - the Common Periwinkle (L. littorea), the Rough Periwinkle (L. saxatilis), and the Smooth Periwinkle (L. obtusata, also called the Flat Periwinkle or Yellow Periwinkle). All have the same general rounded "snail" shape and spend their time grazing on algae in the intertidal, but there are a few ways to tell them apart. The first way is by the height of the spire (the pointy end of the shell). The Smooth Periwinkle has a very low spire, the Common Periwinkle has a blunt and often worn down spite, and the Rough Periwinkle has a relatively high pointy spire. Another way is by looking at the color and grooves of the shell. The Common Periwinkle is usually brownish to black with a white "lip" and has many fine grooves. The Rough Periwinkle is usually yellow-gray with deep grooves. The Smooth Periwinkle varies in color from whitish-yellow to darker brown, and has almost invisible grooves. One final way to distinguish these three is by where they are found. The Rough Periwinkle prefers to be higher in the intertidal than the other two species. The Smooth Periwinkle is usually found on rockweed (Fucus spp.) and knotted wrack (Ascophyllum nodosum), while the Common Periwinkle has a broader range. The Common Periwinkle is actually an introduced species from Europe and as the name suggests, is more common than the other two species.