The Mighty Periwinkle

Jul 25th, 2011 | By | Category: Youth Blog

A Common Periwinkle trail

You can draw a periwinkle!

Have you ever heard of an animal that carries its skeleton on its back? Well, that’s what periwinkles do, plus a whole lot more.

Periwinkles are some of the ocean’s slug-like creatures, belonging to the Gastropod family. The skeleton that they carry on their back is called an exoskeleton. “Exo” means outside. Humans like you have their skeletons inside their bodies.

Since periwinkles have a soft body under their shell, they are able to pull inside their shell and use its operculum like a door to shut and tightly seal the opening on their shell so they are protected from predators and from drying out during low tide. They can also hide from enemies under rocks and sea debris. That was their hiding place until the 1800’s when humans discovered periwinkles on the coast of North America.

Periwinkles are well-adapted creatures that are used to their rocky habitat, even when waves pound on them every few seconds. For how small they are, they are very tough. They are even tough enough to erode rocks over time! Let me tell you how they do that.

Periwinkles eat the algae that grows on the rocks along the ocean shore. They scrape at the algae with their radula which is sort of like their tongue. They scrape at the algae so much, over time, the radula scrapes the rock too.

I didn’t know this until I read a book called The Seaside Naturalist by Deborah A. Coulombe and I’ve learned a lot from that book. It is an illustrated guide to the creatures of the seashore. It teaches me a lot in a very simple way.

Back to the periwinkles, they also leave tracks in the sand when they crawl over it. I took some pictures of the cool tracks when I saw them in Maine. At first I didn’t know why the tracks were there, but then I followed them and found a periwinkle at the end. These trails have mucus in them, which makes the trails. They make the mucus through their foot (a part under the shell). The foot is covered with layers of slimey snot! For kids who don’t live near an ocean and have never seen a periwinkle, they look like garden snails with a shell. (I wonder what cool creatures live in the Midwest that I have never seen, if you know of any, let me know!)

One periwinkle has adapted to living out of the water for short periods of time, and this is called the Common periwinkle, or Littorina Littorea found from Maine to Maryland and is even eaten by some people (UGH!) The Common periwinkle is able to stay out of water by producing extra red blood cells, which provide it with more oxygen when it breathes.

Other than the Common periwinkle, there are 19 other species of periwinkles in North America. Common periwinkles are the most ‘common’ to see, so if you see one, chances are it is that kind. Or you might get lucky and find a Bleeding tooth, Nerita peloronta, with a reddish blood color on the side of its shell. A Four-toothed gastropod has four tooth-shaped pieces on the bottom of its shell. Or you might get extra-lucky and find a Zebra nerite, Puperita pupa a gastropod that has black and white stripes on its shell.

Periwinkles are pretty smart for their size. When the tide goes out, the periwinkle will go with the water and sit on the rocks deeper out in the water. When the tide comes in, that’s when they make their trails.

Periwinkles might be small, but they sure are interesting!

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