Littorina littorea

This is an animal that I spend a lot of time with.  The common periwinkle or little winkle (they have big winkles in Europe) is an introduced species that has become ubiquitous in nearly every Northeast US coastal habitat.  Even though this snail is not native I tend to use the terms "introduced" or "non-native" rather than "invasive" when describing this species.  Terminology related to human introduction can be controversial and I find it varies widely between environmental educators and conservationists.  The reason I choose to describe the periwinkle L. littorea as non-native and not invasive is that it is now a part of the ecology.  It's done whatever damage it's going to do and is now a major presence in the New England inter-tidal. The idea of controlling it or removing it is a joke.  Just go to any inter-tidal in New England, but especially a rocky inter-tidal, a  place like Brant Rock in Marshfield, and you will quickly come to see why I know the l. littorea is here to stay.  This idea of shrugging our shoulders and sort of giving in to invasives is, as I say, a controversial one.  I don't want to dwell on the nuances of the conversation here but if you're interested I recommend the book Out of Eden by Alan Burdick.

That being said, some scientists have put forth the idea that it was the very introduction of L. littorea probably in the mid 19th century that transformed much of the New England coast from marsh flats to rocky inter-tidal.  Perwinkles are voracious grazers and preferentially consume the algae and detritus that hold marsh substrate together.  All snails use a structure called a radula to scrape their food from surfaces (check out this video from youtube) and as these snails became more and more numerous they began scraping the rocks clean.

So besides the unfortunate status of this animal as a once invader I LOVE this snail.  They are one of the world's best observation animals because they are hardy, small, easy to transport and if left unmolested will begin moving around a tank pretty quickly.  They do have the slightly unfortunate requirement of salt water but unlike other inter-tidal inverts they are fairly indifferent to temperature changes.  If you live near the coast in the northeast I highly recommend trying these out with students.