In celebration of the end of summer, my family spent part of Labor Day weekend doing a classic Maine summer activity — beachcombing. We not only look for the special items like the rare piece of blue sea glass or a perfect sand dollar but also have a tradition of looking for the yellowest of the periwinkles that stand out among the more common brown ones washed up onto the shore. They come in a variety of colors ranging from a stripey brown to bright yellow. We call the brightest ones “lemons” and prize them for standing out.
These periwinkles are officially known as Littorina obtusata, their species name referring to their relatively flat shape and giving them their common name of flat periwinkles. They are also sometimes called smooth periwinkles because of their texture. They live on rockweed and look just like the air bladders that dot their long fronds lying over intertidal rocks and in tidepools.
Smooth periwinkles are one of three periwinkle species found in Maine. Periwinkles are some of the most recognizable and accessible species to get to know in the intertidal. You can watch one scoot slowly along the rocks, scraping off algae with its rough tongue-like radula. Or, if you carefully pick one up, you might be lucky enough to see a part of its soft body sticking out from its shell, including its wiggly antennae which sense light and dark and guide the snail on its foraging explorations. More likely than not, it will quickly retract into the safety of its shell and close its snug trap door, or operculum, that seals the vulnerable animal inside. The lore goes, however, that if you hum gently while holding a periwinkle in your hand, it will come back out of its shell. I can testify that this actually often works. I believe it has something to do with the vibrations it causes.
Among the types of Maine periwinkles, the one that is the most common is actually called the “common” periwinkle (Littorina littorea). Despite how common it is, it is actually not native to Maine. It has been here for so long, however, that many people consider it to be native or an “invasive non-invasive.” Common periwinkles were apparently brought to New England in the early 1800s, having hitched a ride on the rocks used as ballast on cargo ships. The third species of periwinkle is the least common — the rough periwinkle (Littorina saxatalis). It is the smallest ‘winkle and has the sharpest spire of the bunch along with having its predictably rough shell.
Aside from differences in appearance, each Maine periwinkle species has a unique way of reproducing. Smooth periwinkles lay their eggs in gooey bunches that hatch into tiny ‘winkles that crawl off onto the rockweed. Common periwinkles release sperm and eggs into the water column, forming planktonic baby ‘winkles that will eventually settle on something hard and complete their development. And rough periwinkle eggs actually develop inside the shell of the mother and then are born live — a rare method for an invertebrate.
Whether you like to find these bright “lemons” on the beach, prefer to hunt for them hiding among the rockweed or pick one up and hum to it to see if you can spy the secretive creature tucked inside that smooth little shell, as often is the case, there is more to see than you might at first imagine from a seemingly simple creature that is so common along the Maine seashore.
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