David Fleetham / Hawaiian swimming crab (Charybdis hawaiensis) regenerating claw after losing it, Hawaii, USA, Pacific Ocean.

Joel Sartore / Photo Ark / Lesser blue crab (Callinectes similis) portrait, Gulf Specimen Marine Lab, Florida, USA. Captive.

Joel Sartore / Photo Ark / Iridescent swimming crab (Portunus gibbesii) dorsal view, Gulf Specimen Marine Lab and Aquarium. Captive.

Joel Sartore / Photo Ark / Lesser blue crab (Callinectes similis) close up, moving antennae and mandibles, Gulf Specimen Marine Lab. Captive.

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

David Fleetham / Ocellate swimming crab (Portunus sebae) on sandy sea floor, photographed off Singer Island, Atlantic Ocean, Florida, USA.

Sergio Hanquet / Swimming crab (Cronius ruber) Canary Islands, Tenerife. Invasive species.

Sergio Hanquet / Swimming crab (Cronius ruber) Canary Islands, Tenerife. Invasive species.

Sergio Hanquet / Swimming crab (Cronius ruber) Canary Islands, Tenerife. Invasive species.