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

Nick Upton / Common Hermit crab (Pagurus bernhardus) in a Common periwinkle shell crawling over floor of a rockpool, Crail, Fife, UK, July.

Nick Upton / Common limpets (Patella vulgata), Common barnacles (Balanus balanoides) and a yellow Rough periwinkle (Littorina saxatilis) nestling in depressions and under an overhang in sandstone rocks high on the...

Nick Upton / Dense gathering of Common periwinkles (Littorina liitorea) of all ages in a rockpool lined with Coralweed (Corallina officinalis) and Irish moss (Chondrus crispus), North Berwick, East Lothian, July

Nick Upton / Dense aggregation of Common periwinkles (Littorina littorea) in a rockpool, North Berwick, East Lothian, UK, July

Nick Upton / Adult Common periwinkle (Littorina liitorea) with well worn shell on rocks encrusted with Common barnacles (Semibalanus balanoides) exposed at low tide, Crail, Fife, July

Nick Upton / Dense gathering of adult and young Common periwinkles (Littorina liitorea) on red sandstone rocks exposed at low tide, North Berwick, East Lothian, July.

Nick Upton / Dense gathering of adult and young Common periwinkles (Littorina liitorea) on red sandstone rocks exposed at low tide, North Berwick, East Lothian, July.

Nick Upton / Dense aggregation of adult and young Common periwinkles (Littorina littorea) in a rockpool, North Berwick, East Lothian, UK, July.

Nick Upton / Dense aggregation of Common periwinkles (Littorina littorea) in a rockpool alongside a variety of red algae, Crail, Fife, UK, July

Nick Upton / Two Common periwinkles (Littorina littorea) crawling over a boulder in a rockpool, Crail, Fife, Lothian, UK, July

Nick Upton / Common periwinkle (Littorina littorea) crawling over rockpool floor, North Berwick, East Lothian, UK, July