Georgette Douwma / Boxer Crab (Lybia tessellata) with sea anemones in its claws for defense. Lembeh Strait, North Sulawesi, Indonesia.

Nick Upton / Common prawns (Palaemon serratus) and a Rock goby (Gobius paganellus) feeding on a dead Montagu's crab (Xantho hydrophilus) in a rockpool, Cornwall, England, UK, September.

Juergen Freund / Mud crab (Scylla serrata) in shallow sandy water. Split level with island and thatched house on stilts. Moromahu Island, Wakatobi, South Sulawesi, Indonesia. Second Place in the Portfolio Award of the...

Hanne & Jens Eriksen / Crab-plover (Dromas ardeola) three walking in a row on mudflat, two with food in beaks. Oman, June.

Magnus Lundgren / Wild Wonders of China / Boxer crab (Lybia tessellata) carrying a sea anemone around in each of its claws, Xiaoliuqiu Island, Taiwan

Alex Mustard / Close up of a tiny Boxer crab (Lybia tessellata) as it waves the stinging anemones it holds in its claws for defence. Tulamben, Bali, Indonesia. Java Sea.

Remi Masson / Crab (Macrophthalmus japonicus), two feeding in mud. Kyushu Island, Japan. August.

Remi Masson / Crab (Cleistostoma dilatatum) in mud. Kyushu Island, Japan. August.

Remi Masson / Japanese mud crab (Macrophthalmus japonicus) feeding in mud, reflected in water. Kyushu Island, Japan. August.

Remi Masson / Crab (Uca sp) with large pincer, in mud. Kyushu Island, Japan. August.

Nick Upton / Montagu's / Furrowed crab (Xantho hydrophilus) from English Channel. South Devon, England, UK. September.

David Fleetham / Splendid round crab (Etisus splendidus) holding pieces of coral that it has broken off with its lobed claws. Philippines.

Magnus Lundgren / Wild Wonders of China / Staff from Ocean Park Conservation Fund, OPCF, and students visit Ha Pak Nai to see the juvenile Chinese horseshoe crabs, (Tachypleus tridentatus) Yuen Long District, New territories, Hong Kong, China...

Magnus Lundgren / Wild Wonders of China / Staff from Ocean Park Conservation Fund, OPCF, and students visit Ha Pak Nai to see the juvenile chinese horseshoe crabs (Tachypleus tridentatus) in a mudflats, Yuen Long District, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Juvenile chinese horseshoe crab (Tachypleus tridentatus) Ha Pak Nai wetlands, Yuen Long District, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Chinese horseshoe crab (Tachypleus tridentatus) juvenile, at Ha Pak Nai wetlands, Yuen Long District, Hong Kong, China. June, 2016.

Magnus Lundgren / Wild Wonders of China / Chinese horseshoe crab (Tachypleus tridentatus) juvenile held upside down in human hand, Ha Pak Nai wetlands, Yuen Long District, Hong Kong, China. June, 2016.

Magnus Lundgren / Wild Wonders of China / Old shells of Chinese horseshoe crab (Tachypleus tridentatus) Ha Pak Nai, Yuen Long District, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Fiddler crab (Uca) male, hiding in an old shell at Ha Pak Nai mudflat, Yuen Long District, Hong Kong, China.

Andy Trowbridge / Sacred / New Zealand Kingfisher (Todiramphus sanctus) perched on driftwood tossing a mud crab. Banks Peninsula, South Island, New Zealand. July.

Andy Trowbridge / Sacred / New Zealand Kingfisher (Todiramphus sanctus) perched on driftwood with mud crab in beak. Banks Peninsula, South Island, New Zealand. July.

Juergen Freund / Mud crabs (Scylla serrata) in the water by the mangrove roots - split level image, Mali Island, Macuata Province, Fiji, South Pacific

Juergen Freund / Mud crabs (Scylla serrata) in the water by the mangrove roots - split level image, Mali Island, Macuata Province, Fiji, South Pacific

Juergen Freund / Mud crabs (Scylla serrata) in the water by the mangrove roots - split level image, Mali Island, Macuata Province, Fiji, South Pacific

Sue Daly / Risso's crab (Xantho pilipes) Sark, British Channel Islands, September.

Nick Upton / Common prawns (Palaemon serratus) feeding on a dead Montagu's crab (Xantho hydrophilus) in a rockpool, Cornwall, England, UK, September.

Nick Upton / Common prawns (Palaemon serratus) feeding on a dead Montagu's crab (Xantho hydrophilus) in a rockpool, Cornwall, England, UK, September.

Nick Upton / Common prawns (Palaemon serratus) and a Shanny (Lipophrys pholis) feeding on a dead Montagu's crab (Xantho hydrophilus) in a rockpool, Cornwall, England, UK, September.

Nick Upton / Common prawns (Palaemon serratus) feeding on a dead Montagu's crab (Xantho hydrophilus) in a rockpool, with a a Rock goby (Gobius paganellus) swimming past, Cornwall, England, UK, September.

Nick Upton / Montagu's crab (Xantho hydrophilus) in a rockpool, showing threat posture with open claws raised, walks out of 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.

Nick Upton / Two Montagu's crabs (Xantho hydrophilus) competing for a crevice to hide in within a rockpool, Cornwall, England, UK, September.

Nick Upton / Montagu's crab (Xantho hydrophilus) moving behind a stone in a rockpool to hide in a rockpool low on the shore, near Falmouth, Cornwall, England, UK, September.

Constantinos Petrinos / Mosaic boxer crab (Lybia tesselata) female carrying its red eggs Lembeh Strait, North Sulawesi, Indonesia

Constantinos Petrinos / Juvenile mosaic reef crab (Lophozozymus pictor) Lembeh Strait, North Sulawesi, Indonesia.

Linda Pitkin / Mosaic reef crab (Lophozozymus pictor), on the reef at night Aljui Bay, Raja Ampat, West Papua, Indonesia.

Bernard Castelein / Marsh crab (Neosarmatium meinerti) collectiing mangrove tree leaves and carrying to its hole, Morombe, Madagascar

Juergen Freund / Fijian expert crab hunter with aggressive Mudcrab (Scylla serrata) in mangroves, Mali Island, Macuata Province, Fiji, South Pacific.

Juergen Freund / Mud crabs (Scylla serrata) in the water by Mangrove roots, split level image, Mali Island, Macuata Province, Fiji, South Pacific.

Juergen Freund / Mudcrab (Scylla serrata) raising claws, Sulawesi, Indonesia

Juergen Freund / Mud crabs (Scylla serrata) in the water by the mangrove roots, split level image. Mali Island, Macuata Province, Fiji, South Pacific.

Pete Oxford / Local woman with string of live Mud crabs (Scylla sp) for sale, Suva Seafood Market, Viti Levu, Fiji, South Pacific, April 2014.

Pete Oxford / Live Mud crabs (Scylla sp) for sale, Suva Seafood Market, Viti Levu, Fiji, South Pacific, April 2014.

Pete Oxford / Live Mud crabs (Scylla sp) and other seafood for sale, Suva Seafood Market, Viti Levu, Fiji, South Pacific, April 2014.

Pete Oxford / Live Mud crabs (Scylla sp) for sale, Suva Seafood Market, Viti Levu, Fiji, South Pacific, April 2014.

Pete Oxford / Live Mud crabs (Scylla sp) for sale, Suva Seafood Market, Viti Levu, Fiji, South Pacific, April 2014.

Pete Oxford / Live Mud crabs (Scylla sp) for sale, Suva Seafood Market, Viti Levu, Fiji, South Pacific, April 2014.

Pascal Kobeh / Boxer / Pompom crab (Lybia tessellata) holding its eggs on hard coral, Manado, Indonesia. Sulawesi Sea.

Pascal Kobeh / Boxer / Pompom crab (Lybia tesselata) with eggs underneath, Manado, Indonesia. Sulawesi Sea.

Ernie Janes / Oystercatcher (Haematopus ostralegus) feeding on crab as tide recedes, Norfolk, East Anglia, England, UK, February.

Sue Daly / Montagu's or Furrowed Crab (Xantho hydrophilus) on sea shore, Sark, British Channel Islands.

Sue Daly / Risso's crab (Xantho pilipes) on sea shore, Guernsey, British Channel Islands.

Anup Shah / Long-tailed macaques (Macaca fascicularis) foraging on the mudflats at low tide. Bako National Park, Sarawak, Borneo, Malaysia.

Anup Shah / Long-tailed macaque (Macaca fascicularis) female carrying a baby under her belly walking across the mudflats of a mangrove swamp revealed at low tide - wide angle perspective. Bako National Park, Sar...

Anup Shah / Long-tailed macaque (Macaca fascicularis) walking through the mudflats of a mangrove swamp revealed at low tide - wide angle perspective. Bako National Park, Sarawak, Borneo, Malaysia. Mar 2010.

Anup Shah / Long-tailed macaque (Macaca fascicularis) walking through the mudflats of a mangrove swamp revealed at low tide - wide angle perspective. Bako National Park, Sarawak, Borneo, Malaysia. Mar 2010.

Franco Banfi / Button crab (Paractaea monodi) on encrusting red sponge, Ponza Island, Italy, Tyrrhenian Sea, Mediterranean

Cyril Ruoso / Giant Mud Crab (Scylla serrata) with claws spread wide in defensive posture, Mahakam Delta, Indonesia

Nick Upton / Herring gull (Larus argentatus) eating a Shore crab (Carcinus maenas) which it has caught in the Looe estuary at low tide, Cornwall, UK, June.

Nick Upton / Herring gull (Larus argentatus) pecking at a Shore crab (Carcinus maenas) which it has caught in the Looe estuary at low tide, Cornwall, UK, June.

Fabio Liverani / Freshwater Crab (Potamon fluviatile) on pile of mud dug out of hole. Foreste Casentinesi National Park, Italy, August.

Fabio Liverani / Freshwater Crab (Potamon fluviatile) on pile of mud dug out of hole. Foreste Casentinesi National Park, Italy, August.

Fabio Liverani / Freshwater Crab (Potamon fluviatile) on pile of mud dug out of hole. Foreste Casentinesi National Park, Italy, August.

Tim Laman / Silas, headman of Kabilo Village holding a Giant Mud Crab, caught whilst spearfishing at night from canoes in Mayalibit Bay. Waigeo Island, West Papua, Indonesia, April 2007

Michele Westmorland / Mud crab on the banks of the Indian river, Dominica, West Indies, Caribbean. July.

Tim Laman / Photographer's muddy feet from walking through mangrove mud with a fiddler crab emerging from hole between the feet, Bako National Park, Sarawak, Borneo, Malaysia. June 2006

Tim Laman / Fiddler crab {Uca sp} emerging from its burrow in the mangrove mud to forage during low tide, Sundarban Forest, Khulna Province, Bangladesh.

Tim Laman / Mudskippers {Periophthalmus sp} climbing into the shell of a mangrove crab on the mud flats at low tide, Sundarbans, Khulna Province, Bangladesh.

Tim Laman / Fiddler crab {Uca sp} emerging from its burrow in the mangrove mud to forage during low tide, Sundarban Forest, Khulna Province, Bangladesh.

Bernard Castelein / Mud crab ( Lydia annulipes) Zanzibar, Tanzania

Willem Kolvoort / Fiddler crab (male Uca genus) on muddy coast near Paramaribo, Suriname

Kim Taylor / Mud crab {Scylla serrata} emerging from its turret amongst mangrove, Trinidad, West Indies.

Kim Taylor / Fiddler crabs {Uca tangeri} feeding in mud at low tide. Africa.

Michael & Patricia Fogden / Fiddler Crab (Uca sp) in mud, Darwin, Northern Territory, Australia

Anup Shah / Crab eating / Long tailed macaque (Macaca fascicularis) feeding on crab at low tide in mangrove area, Sumatran Coast Indonesia

Anup Shah / Long-tailed Macaque (Macaca fascicularis) juvenile foraging in mangrove swamp, Bako National Park, Sarawak, Borneo, Malaysia

Piotr Naskrecki / Japanese Horseshoe Crab (Tachypleus tridentatus) in shallow, muddy waters very close to the shore, Japan

Alan James / Mud runner crab {Goneplax rhomboides} on seabed, UK

Jack Perks / Thornback ray (Raja clavata) entering frame and feeding on Green crab (Carcinus maenas) before leaving frame, followed by Spurdog (Squalus acanthias) which swims through frame. Whiting (Merlangius mer...

Joel Sartore / Photo Ark / Boxer crab (Lybia tessellata) portrait, National Aquarium, Abu Dhabi. Captive, occurs in Indo-Pacific Ocean.

Alex Mustard / Shaggy crab (Zalasius dromiaeformiss) resting on the seabed at night, Bitung, North Sulawesi, Lembeh Strait, Molucca Sea.

Tony Wu / Pair of Mud crabs (Scylla sp.) preparing to mate in late summer, where male is on top and female upside-down beneath. Sea of Japan, Yamaguchi Prefecture, Japan.

Tony Wu / Female Mud crab (Scylla sp.) carrying eggs during late summer. Sea of Japan, Yamaguchi Prefecture, Japan.

Ripan Biswas / Mangrove horseshoe crabs (Carcinoscorpius rotundicauda) pair mating in mud at dawn, Sunderban tiger reserve, West Bengal, India.

Andy Trowbridge / New Zealand kingfisher (Todiramphus sanctus) in flight with Mud crab in beak, Banks Peninsula, South Island, New Zealand.

Alex Mustard / Hoary rubble crab (Banareia palmeri) gripping on to a sea rod, Grand Cayman, Cayman Islands, Caribbean Sea.

David Fleetham / An endemic Hawaiian pom-pom crab / Boxer crab (Lybia edmondsoni) carrying a juvenile Anemone (Triactis producta) in its claws as a defense mechanism. A mutualistic symbiosis, with the anemone being tr...

Tony Wu / Japanese horseshoe crabs (Tachypleus tridentatus) eggs deposited in shallow gravel and mud, Japan, Pacific Ocean.

Claudio Contreras / Mexican fiddler crab (Leptuca crenulata) small male displaying with larger individual behind, Morua Estuary, near Rocky Point (Puerto Peñasco), Gulf of California, Mexico, June.

Claudio Contreras / Mexican fiddler crab (Leptuca crenulata) small male displaying with larger individual behind, Morua Estuary, near Rocky Point (Puerto Peñasco), Gulf of California, Mexico, June.

Claudio Contreras / Mexican fiddler crab (Leptuca crenulata) small male displaying with larger individual behind, Morua Estuary, near Rocky Point (Puerto Peñasco), Gulf of California, Mexico, June.

Claudio Contreras / Mexican fiddler crab (Leptuca crenulata) small male displaying with larger individual behind, Morua Estuary, near Rocky Point (Puerto Peñasco), Gulf of California, Mexico, June.

Bruce Thomson / Orange clawed fiddler crab (Uca coarctata) male in tidal mud flat, Manly, Brisbane, Australia.

Bruce Thomson / Two toned fiddler crab (Uca vomeris) male in tidal mud flat, Manly, Brisbane, Australia.

David Fleetham / Pom-pom crab / Mosaic boxer crab (Lybia tesselata) carrying large egg mass and its associated Anemone (Triactis producta), used for defense. that it carries around in its claws, using them for defense...