Range: Worldwide

Habitat: Marine shorelines

Size: 1.5 inches (4 cm) shell length

Diet: Algae, invertebrate eggs and larvae and more

Threats: Birds, fish, fluke worms, crabs, sea stars and more

Lifespan: Five years in the wild

Transcript:

Today on Animal Fact Files we’re discussing periwinkles. Periwinkles are also known simply as “winkles,” and some species are referred to as edible periwinkles because humans eat them. Periwinkles are snails. They’re mostly marine snails, meaning they predominantly live in the ocean, but these invertebrates can tolerate brackish water and even freshwater for short periods of time. In some parts of the world, such as the United States, any small, marine snail with a spiral shell may be referred to as a periwinkle, or a pennywinkle, but this video is focusing specifically on the Littorina genus and their relatives. Periwinkles have spiral shells which help withstand wave action– the shell makes it so waves can not as easily knock the snail from where it’s grazing.

Periwinkles live world wide, and they most frequently inhabit coastlines. This is also known as the littoral zone to which their genus name alludes. Periwinkles spend a majority of their time on rocky shores with solid or pebbled stone, mud flats, and sometimes even the roots of mangrove trees or among blades of marsh grass. They form massive aggregations where there may be thousands of periwinkles in a 10 square foot (1 m^2) area. It’s also not uncommon for them to gather in crevices. These snails are small with shells rarely reaching more than 1.5 inches (4 cm) in length. Like land snails, they have tentacles that help them sense the world around them with sight and taste. They also have a shell lid, known as an operculum, which they use to seal in moisture and seal out predators.

Periwinkles are eaten by a variety of species. Birds such as gulls, knots, and especially ducks, all consume these tasty molluscs. Periwinkles are actually part of a parasitic cycle in which they are an intermediary host to fluke worms. The snails eat bird poop– bet you didn’t see that one coming! Although these trematodes ultimately need to end up in a bird to reproduce, they first must pass through a periwinkle snail which is then eaten by a fish, which is then consumed by the final host– a bird. Many fish species eat periwinkles including flounders! Crabs, sea stars, worms, and even other snails also eat periwinkles! All these predators might seem like a detriment to the snails, but if left unchecked, periwinkles could completely erode the shoreline!

These invertebrates gather in massive numbers. They eat by using a tooth-cover tongue– called a radula, to scrape at the surface of the substrate they live on. A group of them can slowly, over time, change the shape of a rock, or potentially even make it disappear altogether if given enough time. Although periwinkles are technically herbivores, specifically targeting algae and grasses, their method of eating means they ingest not just animal material in the form of eggs and larvae of other animals, they also take in inorganic matter, like rocks! So it’s important for them to have predators to keep the ecosystem in balance.

Although these are snails, periwinkles have separate sexes. Not only that, they have many different reproduction strategies. Some broadcast spawn and their floating eggs are fertilized externally, drifting through the waves for about a week before the larvae settle to the seafloor. Others Release their eggs so they’ll collect in seaweed and remain there for a few weeks before hatching. Others brood their eggs, keeping them close until they hatch and are only released at that point looking like teeny, tiny versions of the adults. It takes about a year for them to reach reproductive size, and they can live for 5 years in the wild, or potentially longer– some people report periwinkles living over a decade in home aquariums!

Okay I saved this last little bit of information for the end because it, personally, makes my skin crawl. Let this be your warning: if barnacles bother you, look away now! When periwinkles die, their shells are often recycled as homes for hermit crabs. Other animals also use periwinkle shells for their homes, including barnacles. In fact, these boring arthropods will actually take up residence on a periwinkle shell while the snail is still alive!

For more facts on periwinkles, check out the links below. Give a thumbs up if you learned something new today. Thank you to our Patrons SpikeSpiegel93, Dad, and everyone else for their support of this channel! And thank you for watching Animal Fact Files!