Sergio Hanquet / Arrow crab (Sternorhynchus lanceolatus). Tenerife, Canary Islands.

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

Steven David Miller / Sand bubble patterns created by Sand bubbler crabs (Scopimera inflata), Cape Hillsborough National Park, Queensland, Australia. September.

Juergen Freund / Wide-angle timelapse of Sand bubbler crabs (Dotillidae) feeding, filtering detritus and plankton from sand and discarding the processed sand as pellets, which cover the beach, Wet Tropics World Herita...

Juergen Freund / Sand bubbler crabs (Dotillidae) feeding, filtering detritus and plankton from sand and discarding the processed sand as pellets, which cover the beach, Wet Tropics World Heritage Area, Cape Tribulatio...

David Fleetham / Hawaiian pom-pom / boxer crab (Lybia edmondsoni)with anemones (Triactis sp) that it carries around holding with the claws and using them for defense, waving in front of the possible aggressor. An exam...

Ingo Arndt / Rear view of Horseshoe crab (Limulus polyphemus) with trail in sand, Delaware Bay, Delaware, USA, May

Ingo Arndt / Blue Crab (Discoplax hirtipes) with claws raised in defensive / aggressive posture, endemic to Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Blue Crab (Discoplax hirtipes) with claws raised in defensive / aggressive posture, endemic to Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crab (Gecarcoidea natalis) blurred view of vast number of individuals moving along their annual migration route, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Robber / Coconut Crab (Birgus latro) close up of head and legs, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) crossing closed road, during annual migration, Christmas Island, Indian Ocean, Australian Territory, November 2009.