Alex Hyde / Selection of gastropods commonly found in rockpools, clockwise from top left: Periwinkle (Littorina compressa / nigrolineata), Dogwhelk (Nucella lapillus / Thaius lapillus), Common Flat Periwinkle (Li...

Alex Hyde / Common Flat Periwinkle (Littorina obtusata / littoralis) against white background. From the Isle of Skye, Inner Hebrides, Scotland, UK.

Alex Mustard / 2020VISION / Flat periwinkle (Littorina obtusata) feeding on kelp frond, Loch Carron, Ross and Cromarty, Scotland, UK, April

Philippe Clement / Shells of the Flat periwinkle (Littorina obtusata) showing colour variation, Brittany, France

Robert Thompson / Periwinkle {Littorina obtusata} camouflaged on seaweed, Ballyhenry Point, Strangford Lough, County Down, Northern Ireland, UK, September

Philippe Clement / Flat periwinkle (Littorina obtusata) shell on beach, Mediterranean, France

Philippe Clement / Flat periwinkle (Littorina obtusata) shell, Mediterranean, France

Philippe Clement / Flat periwinkle (Littorina obtusata) shell showing the aperture, Mediterranean, France