Littorina saxatilis has a rounded shell, up
to 1/2 inch in width. It is sometimes difficult to identify rough
periwinkles, since they closely resemble the juvenile common periwinkle.The
opening or aperture of the shell is large and rounded, with an outer
lip that sticks out slightly. Shell color can vary, as shown in the
image above- yellowish white, greenish, reddish, brown, or white. Current
research is attempting to explain the color variation. One theory is
that the color variation is tied to the substrate color, which suggests
an adaptation related to camoflauge. The green color of L.
saxatilus is most likely caused by a green algae that
burrows into the snail's shell.
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Here's an idea...
If the rocky shore is accessible to you, make your own observations
about shell color in rough periwinkles. First identify which color
variations you will focus on. Second select your location. Third
make comparisons and take notes on what you observe about where you
find particular colors in specific intertidal areas. While you are
compiling your observations, make note of the surrounding environment,
type of substrate and color, the time of day, season, the time of
the tide cycle, the weather-these all may influence your observations.
You will need to repeat your observations a few times to see a pattern.
Once you have some information, write a statement that sums up what
you observed, i.e. "Rough periwinkles that are mostly white
in color always appeared in and around barnacles at low tide during
the first week in June 2005 at Blake's Cove."
Send your statement to Mitzi and see it posted on the website.
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