Shells adapted to resist crab attack by their long spire into which animal can retreat, and by their thick shell which resists crushing by crabs and constricts the aperture to reduce access for attack. Usually found on sheltered shores which favour the crab, Carcinus maenas.

Left: Spire 55% of shell height. South Wales, October 2023. © P. Challinor

Right: Spire height (1) 43% of shell height. Menai Strait, Wales. August 2009.