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

Juergen Freund / Arrow crab on sponge (Stenorhynchus seticornis) Caribbean

Juergen Freund / Arrow crab on brain coral {Stenorhynchus seticornis} Caribbean Sea, Cuba

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

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

Shane Gross / Arrow crab (Stenorhynchus seticornis) on coral. Eleuthera, Bahamas.

Pascal Kobeh / Yellowline arrow crab (Stenorhynchus seticornis / lanceolatus), Canary Islands

SCOTLAND: The Big Picture / Common spider crab (Macropodia rostrata) on maerl, South Arran Marine Protected Area, Isle of Arran, Scotland, UK, August.

SCOTLAND: The Big Picture / Common spider crab (Macropodia rostrata) on maerl, South Arran Marine Protected Area, Isle of Arran, Scotland, UK, August.

Graham Eaton / Yellowline Arrow Crab (Stenorhynchus seticomis) in an Azure Vase Sponge (Callyspongia plicifera). St Lucia, West Indies, July.

Michele Westmorland / Spotted Moray Eel (Gymnothorax moringua) with mouth open, and Arrow crab (Stenorhynchus seticornis) in healthy coral reef system, Dominica, West Indies, Caribbean.

Michele Westmorland / Spotted Moray Eel (Gymnothorax moringua) with mouth open, and Arrow crab (Stenorhynchus seticornis) in healthy coral reef system, Dominica, West Indies, Caribbean.

Chris Newbert / Arrow Crab (Stenorhynchus seticornis) in Anemone (Heteractis sp) 60 feet deep, Caribbean

Doug Perrine / Diver photographs Arrow crab {Stenorhynchus seticornis} on spnge, St Croix, Caribbean

Michael & Patricia Fogden / Magenta-throated Woodstar (Calliphlox bryantae) hummingbird male flying near Latin American Lady Orchid (Stenorrhynchos speciosum) cloud forest, Costa Rica

Michael & Patricia Fogden / Magenta-throated Woodstar (Calliphlox bryantae) hummingbird male flying near Latin American Lady Orchid (Stenorrhynchos speciosum) cloud forest, Costa Rica

Norbert Wu / Arrow Crab (Stenorhynchus seticornis) long spindly arms around central arrow-shaped body, Caribbean

Constantinos Petrinos / Spotted moray eel {Gymnothorax moringua} and spider crab {Stenorhynchus seticornis} Bonaire, Caribbean

Juergen Freund / Arrow crab (Stenorhynchus seticornis) on fan coral. Caribbean

Roberto Rinaldi / Arrow crab (Stenorhynchus setircornis), Belize

Roberto Rinaldi / Arrow crab (Stenorhynchus setircornis), Belize.

Angelo Giampiccolo / Arrow crab (Stenorhynchus seticornis) on tube sponge at night, Belize Cayes, Caribbean.

Angelo Giampiccolo / Arrow crab (Stenorhynchus seticornis) in tube sponge at night, Belize Cayes, Caribbean.

Angelo Giampiccolo / Arrow crab (Stenorhynchus seticornis) on a tube sponge at night, Belize Cayes, Caribbean.

Angelo Giampiccolo / Arrow crab (Stenorhynchus setircornis) on tube sponge, at night in the Belize Cayos, Caribbean.

Angelo Giampiccolo / Arrow crab (Stenorhynchus seticornis) in a tube sponge at night, Belize Cayes, Caribbean.

Angelo Giampiccolo / Arrow crab (Stenorhynchus seticornis) inside tube sponge at night, Belize Cayes, Caribbean.

Roberto Rinaldi / Yellowline arrow crab (Stenorhynchus seticornis), on white gorgonian sea fan / lace sea fan (Eunicella singularis), Cayos Cochinos, Honduras.

Jordi Chias / Arrow crabs (Stenorhynchus lanceolatus) pair, female underneath male after mating, male is guarding the fertilised eggs from other male Arrow crabs, protected from predators by Sea urchin quills, Gran...

Alex Mustard / Arrow crab (Stenorhynchus seticornis) resting in its home inside a Brown tube sponge (Agelas conifera), Grand Cayman, Cayman Islands, Caribbean Sea.

David Hall / Yellowline arrow crab (Stenorhynchus seticornis) feeding on an unidentified segmented worm, probably a polychaete tube worm (Sabellidae), Dominica, Caribbean, Western Atlantic Ocean.

David Hall / Yellowline arrow crab (Stenorhynchus seticornis) living in association with Giant Caribbean sea anemone (Condylactis gigantea), Dominica, Caribbean.

Claudio Contreras / Panamic arrow crab (Stenorhynchus debilis), on fan coral, San Rafaelito Lighthouse Islet, Balandra National Protected Area, near La Paz, Gulf of California (Sea of Cortez), Mexico, September

Claudio Contreras / Panamic arrow crab (Stenorhynchus debilis), Puerto Escondido, Loreto Bay National Park, Gulf of California (Sea of Cortez), Mexico, August

Claudio Contreras / Yellowline arrow crab (Stenorhynchus seticornis), Cozumel Island, Caribbean Sea, Mexico.

Claudio Contreras / Yellowline arrow crab (Stenorhynchus seticornis), Cozumel Island, Caribbean Sea, Mexico.

Claudio Contreras / Yellowline arrow crab (Stenorhynchus seticornis) with featherstar, Cienaga de Zapata National Park, Matanzas Province, Cuba.

Franco Banfi / Several arrow crab (Stenorhynchus lanceolatus) and green moray, South Tenerife, Canary Island.

Franco Banfi / Couple of Arrow Crab (Stenorhynchus lanceolatus) mating in front of a sea urchin, South Tenerife, Canary Islands, Atlantic Ocean.

Robert Pickett / Arrow Crab (Stenorhynchus seticornis) occurs in Atlantic Ocean, captive.