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.

Nick Upton / Two Montagu's crabs (Xantho hydrophilus) competing for a crevice to hide in within a rockpool, with a young Velvet swimming crab (Necora puber) moving away nearby, 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.