More about the Common periwinkle
The Common periwinkle can be found in
concentrations of up to several hundred per square metre in most beach
environments. They are even common in estuaries, where freshwater mixes
with salt water, because they are able to tolerate water with a salinity
down to 10 parts per thousand. They can even be found on soft bottoms,
but there must be a few hard objects such as rocks, piles, seaweed or
mussel banks for it to flourish.
It is quite easy to find periwinkles, when
they creep along a sand bottom, they usually leave a 1 cm
wide trail after them. Normally they move at a speed of
about 1-2,5 m an hour, but if they are in a real hurry they
can attain speeds of up to 5 m an hour. It is asserted that
periwinkles return to the "hard bottom" after they have been
out rumaging after food on the sand. You can test to see if
this is true on the beaches you visit.
Glue their shell
The Common periwinkle combats dehydration
very well. Periwinkles can survive out of the water for several weeks.
They protect themselves by withdrawing into their shells and closing the
aperture with a hornlike lid (operkulum) that is situated above their
foot. When they have withdrawn into the shell, they have trouble holding
onto the substrate. To avoid falling off stones
and rocks into deep water, they secrete a mucus from their foot that
hardens in the air. This "glues" the shell lightly onto the rock.
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