Crab
The brown crab Cancer pagurus wears a thick exoskeleton of highly mineralized chitin. This species belongs to the Brachyura, known as true crabs. Yet another group called horseshoe crabs lives in the late Ordovician period of Canada around 445 million years ago. These ancient creatures belong to Chelicerata alongside spiders and scorpions. Their body plan differs significantly from true crabs despite sharing an armored carapace. True crabs and many Anomura groups like king crabs evolved independently through carcinisation. This process created similar body forms across multiple decapod lineages without a single common ancestor. Scientists describe this polyphyletic nature as having multiple evolutionary origins rather than one natural group. The result is a diverse collection of animals that look alike but do not share a recent lineage.
A pea crab measures only a few millimeters wide while the Japanese spider crab spans up to several meters with its legs. The coconut crab Birgus reaches lengths of up to half a meter and weighs over four kilograms on Pacific islands. It stands as the largest terrestrial arthropod existing today. Porcelain crabs hide under rocks and often shed limbs to escape predators. The hairy stone crab Lomisidae moves slowly along the Australian shore covered in brown hair for camouflage. King crabs Lithodidae live mainly in cold deep water yet resemble brachyurans more closely than hermit crabs. Patagurus rex lives at depths of 400 metres near Polynesia with a unique carapace structure. These variations show how different species adapted their physical forms to survive specific environments.
The tufted ghost crab Ocypode cursor consumes insects and other terrestrial animals while remaining semi-terrestrial. Parasitic pea crabs Pinnotheridae live inside bivalve molluscs feeding on their hosts' food supplies. The mottled crab Grapsus albolineatus eats algae preferring filamentous types over leafy varieties. Yellow moon crabs Ashtoret lunaris hunt small animals as carnivores. Porcelain crabs filter plankton from seawater using long feathery bristles on their mouthparts. Some 1,300 crab species inhabit freshwater environments across eight families. Christmas Island red crabs migrate annually to the sea to lay eggs despite living on land as adults. Tree crabs breathe air through lungs and take over mollusc shells for protection after molting.
Crabs account for approximately 20% of all marine crustaceans caught or farmed worldwide totaling 1.5 million tonnes each year. The Asian blue crab Portunus trituberculatus represents one-fifth of that total catch volume alone. Brown crabs Cancer pagurus provide sweet delicate meat for British cuisine where dressed crab remains a traditional meal. Commercial fisheries operate in Scotland and South West England harvesting these creatures regularly. Blue crabs Callinectes sapidus support major operations along the Atlantic coast and Gulf of Mexico in North America. Crab cakes traditionally use Chesapeake Bay specimens though other regions now contribute significantly to production. Goa and Mozambique prepare crab curry flavored with chilis garlic coconut and local spices. Snow crab males kano-gani and females kobako-gani appear as sushi delicacies in Ishikawa prefecture Japan during winter months.
Greek mythology features Karkinos a crab aiding the Lernaean Hydra against Heracles though it sometimes appears omitted from retellings. Astrologers may have introduced this element through Mesopotamian influence linking Hercules labors to Zodiac signs. Moche people of ancient Peru worshipped nature and frequently depicted crabs in pottery and murals. Albrecht Dürer painted Eriphia verrucosa meticulously in 1495 likely during his visit to Venice on the Adriatic coast. The Barbizet Studio created monumental crab table chargers between 1850 and 1890 using glazed earthenware techniques. Gao Qipei painted Crabs and Chrysanthemums in ink and light watercolour on paper between 1672 and 1734. Rudyard Kipling wrote The Crab that Played with the Sea describing how tides rise and fall due to a giant creature's movements. Malay mythology attributes ocean tides to water rushing into the Navel of the Seas where a gigantic crab searches for food twice daily.
Caribbean hermit crabs Coenobita clypeatus live up to thirty years in captivity when their needs are met properly. Owners must simulate coastal rainforest conditions within substantial tanks containing sand and coconut fibre substrates. These crabs require controlled air temperature and humidity levels throughout their lifespan. Freshwater pools alongside correctly formulated salt water pools remain essential components of any habitat setup. Moulting demands digging capabilities so substrate depth matters significantly for successful molting cycles. Hermit crabs breathe air through lungs unlike many marine relatives yet still need access to both fresh and salt water sources. Aquarium trade relies heavily on these species despite their complex environmental requirements for long-term survival.
Zoologist Joanna Wolfe notes a popular internet joke claiming everything will eventually evolve into crabs as ultimate forms. This meme parodies the genuine process of carcinisation occurring across at least five decapod groups independently. Evolutionary palaeobiologist Matthew Wills explains that evolutionary pressures apply specifically to marine environments favoring armoured protection. Predation living in crevices and wave-swept habitats drive adaptations like broad compact bodies and sideways scuttling abilities. Humans or other animals do not share these specific evolutionary pressures driving crab-like traits. The scientific reality shows distinct lineages converging on similar forms rather than all life progressing toward one endpoint. Decapods span multiple crab-like groups including true crabs but excluding unrelated organisms entirely.
Common questions
What is the scientific classification of the brown crab Cancer pagurus?
The brown crab Cancer pagurus belongs to the Brachyura group known as true crabs. This species wears a thick exoskeleton made of highly mineralized chitin.
When did horseshoe crabs live in Canada during the Ordovician period?
Horseshoe crabs lived in Canada around 445 million years ago during the late Ordovician period. These ancient creatures belong to Chelicerata alongside spiders and scorpions.
How much does the coconut crab Birgus weigh on Pacific islands?
The coconut crab Birgus weighs over four kilograms while reaching lengths of up to half a meter. It stands as the largest terrestrial arthropod existing today.
Which Asian blue crab Portunus trituberculatus represents one-fifth of global catch volume?
The Asian blue crab Portunus trituberculatus represents one-fifth of the total annual catch volume worldwide. Crabs account for approximately 1.5 million tonnes caught or farmed each year globally.
Who painted Eriphia verrucosa meticulously in 1495 during his visit to Venice?
Albrecht Dürer painted Eriphia verrucosa meticulously in 1495 likely during his visit to Venice on the Adriatic coast. This artwork documents the species with high detail.