John Shaw / Sally lightfoot crabs (Grapsus grapsus) on the beach at Puerto Egas, Santiago Island, Galapagos, May.

Nick Upton / Velvet swimming crab (Necora puber) in a rock pool, waving and opening one of its claws in a threat display, Cornwall, England, UK, September.

Nick Upton / Velvet swimming crab (Necora puber) moving off, leaves frame, Cornwall, England, UK, September.

Sue Daly / Male Velvet swimming crab (Necora puber) guarding female prior to mating, Sark, British Channel Islands, UK, August.

Sue Daly / Male Velvet swimming crab (Necora puber) guarding a female prior to mating, Sark, British Channel Islands, UK, August.

SCOTLAND: The Big Picture / Harbour crab (Liocarcinus depurator) in maerl bed, South Arran Marine Protected Area, Isle of Arran, Scotland, UK, August.

SCOTLAND: The Big Picture / Harbour crab (Liocarcinus depurator) in maerl bed within no take zone, South Arran Marine Protected Area, Isle of Arran, Scotland, UK, August.

SCOTLAND: The Big Picture / Harbour crab (Liocarcinus depurator) in maerl bed, South Arran Marine Protected Area, Isle of Arran, Scotland, UK, August.

Sue Daly / Female Harbour Crab with eggs (Liocarcinus depurator) Bouley Bay, Jersey, British Channel Islands.

Franco Banfi / Portunid crab (Liocarcinus depurator), mating pair, Vevang, Norway, Atlantic Ocean.

Franco Banfi / Portunid crab (Liocarcinus depurator) scuttling across the seabed, Trondheimfjord, Norway, North Atlantic Ocean.