Nick Upton / Flat periwinkle (Littorina obtusata / littoralis) yellow form crawling over rocks exposed at low tide, Cornwall, UK, March.

Nick Upton / Flat periwinkle (Littorina obtusata), yellow form crawling over Spiral wrack (Fucus spiralis). Treyarnon Bay, Cornwall England, UK. September.

Nick Upton / Flat periwinkle (Littorina obtusata), yellow form from Atlantic Ocean. Cornwall, England, UK. September.

Alex Hyde / Common Hermit Crab (Pagurus bernhardus) in Flat Periwincle shell (Littorina obtusata). Isle of Mull, Scotland, UK. June.

Sue Daly / Smooth periwinkles (Littorina obtusata) on kelp, Derrible Bay, Sark, British Channel Islands.

Alex Hyde / Common Hermit Crab (Pagurus bernhardus) in shell of Edible Periwinkle (Littorina littorea). This close up shows the compound eyes. Northumberland, UK. May.

Alex Hyde / Common Hermit Crab (Pagurus bernhardus) in shell of Edible Periwinkle (Littorina littorea). Photographed on a white background in mobile field studio. Northumberland, UK. May.

Alex Hyde / Common Hermit Crab (Pagurus bernhardus) in shell of Edible Periwinkle (Littorina littorea). Photographed on a white background in mobile field studio. Northumberland, UK. May.

MYN / Carsten Krieger / Flat Periwinkle (Littorina obstusata) from rock pool, County Clare, Republic of Ireland, August. Meetyourneighbours.net project

MYN / Carsten Krieger / Flat Periwinkle (Littorina obtusata) from tide pool, County Clare, Republic of Ireland, August. Meetyourneighbours.net project

MYN / Carsten Krieger / Flat Periwinkle (Littorna obtusata) on Bladderwrack (Fucus vesiculosus) from tide pool, County Clare, Republic of Ireland, December. Meetyourneighbours.net project

Nick Upton / European oyster drill / Sting winkle (Ocenebra erinacea) a pest of oyster beds, on rocks low on the shore alongside Acorn barnacles (Balanus perforatus) exposed at low tide, with seaweed, rock pools a...