Crab — Mediated Wiki

{{Short description|Group of crustaceans}} {{good article}} {{pp-move-indef|small=yes}} {{Use British English|date=November 2025}} {{Use dmy dates|date=November 2025}}

{{About|the crustaceans|other uses}} [[File:Cancer pagurus.jpg|thumb|upright=1.35|''Cancer pagurus'', the edible or brown crab (Brachyura)]] '''Crabs''' are decapod crustaceans, either the Brachyura (the "true crabs") or various groups within the closely related Anomura (hermit crabs and allies), characterised by having a heavily armoured shell, their tail segments concealed under the body, the ability to run sideways, and the habit of hiding in rocky crevices. They do not form a single natural group or clade, but have convergently evolved multiple times from the ancestral decapod body plan through carcinisation, the process of creating this set of characteristics. As a group, they are thus polyphyletic, meaning they have multiple evolutionary origins.

Crabs vary in size from the pea crab, a few millimeters wide, to the Japanese spider crab, with a leg span up to {{convert|4|m|ft|abbr=on}}. Many crabs are free-living marine omnivores; others are specialist herbivores or carnivores, while some are parasitic. A substantial number of species are adapted to freshwater or other non-marine habitats.

Crabs make up about 20% of the marine crustaceans that are caught or farmed for human consumption. In British cuisine, dressed crab is a traditional seafood meal, while in Goa and Mozambique, crab curry is a typical dish. Crabs feature in Greek and Malay mythology, and as the astrological sign Cancer. They have appeared in art in media including pottery, paintings, blouse panels, and book illustrations. Hermit crabs are often kept in aquariums and as pets. A popular meme jokes that everything will evolve into crabs, based inaccurately on the genuine evolutionary trend within the decapods.

== Diversity ==

=== Taxonomic range ===

==== Phylogeny ====

Crabs are not a single taxonomic group.<ref name="Keiler 2014"/> Instead, alongside the Brachyura or true crabs, are multiple groups of the Anomura that are called crabs, including the hermit crabs, mole crabs, king crabs, and porcelain crabs.<ref name="Bracken-Grissom 2013">{{cite journal |last1=Bracken-Grissom |first1=Heather D. |last2=Cannon |first2=Maren E. |last3=Cabezas |first3=Patricia |last4=Feldmann |first4=Rodney M. |last5=Schweitzer |first5=Carrie E |last6=Ahyong |first6=Shane T. |last7=Felder |first7=Darryl L. |last8=Lemaitre |first8=Rafael |last9=Crandall |first9=Keith A. |display-authors=5 |title=A comprehensive and integrative reconstruction of evolutionary history for Anomura (Crustacea: Decapoda) |journal=BMC Evolutionary Biology |volume=13 |issue=1 |date=2013 |pmid=23786343 |pmc=3708748 |doi=10.1186/1471-2148-13-128 |doi-access=free |page=128 |bibcode=2013BMCEE..13..128B }}</ref> A distantly-related group of arthropods, the horseshoe crabs, with an armoured carapace but a quite different body plan, is a member of the Chelicerata, the group that includes the spiders and scorpions.<ref name="Garw3">{{cite journal |last1=Garwood |first1=R. J. |last2=Dunlop |first2=J. |date=13 November 2014 |title=Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders |journal=PeerJ |volume=2 |article-number=e641 |doi=10.7717/peerj.641 |pmc=4232842 |pmid=25405073 |bibcode=2014PeerJ...2.e641G |doi-access=free}}</ref> The crab body form and associated behaviour have arisen independently at different times in multiple groups of decapod crustaceans ('''boldface''' in tree).<ref name="Keiler 2014">{{cite journal |author1=Jonas Keiler |author2=Stefan Richter |author3=Christian S. Wirkner |year=2014 |title=Evolutionary morphology of the organ systems in squat lobsters and porcelain crabs (Crustacea: Decapoda: Anomala): an insight into carcinization |journal=Journal of Morphology |volume=276 |issue=1 |pages=1–21 |doi=10.1002/jmor.20311 |pmid=25156549 |bibcode=2015JMorp.276....1K |s2cid=26260996 }}</ref>

{{clade |label1=Arthropoda |1={{clade |label1=Chelicerata |sublabel1=''Middle Cambrian'' |1={{clade |label1=Xiphosura |1=('''horseshoe crabs''') 75 px |sublabel1=''Late Ordovician'' |2=other chelicerates (spiders, scorpions) }} |label2=Mandibulata |2={{clade |1=other crustaceans |label2=Decapoda |2={{clade |1=other decapods (prawns, shrimps, lobsters) |2={{clade |label1=Brachyura |sublabel1=''Early Jurassic'' |1=('''"true" crabs''')<ref>{{cite journal |author1=C. L. Morrison |author2=A. W. Harvey |author3=S. Lavery |author4=K. Tieu |author5=Y. Huang |author6=C. W. Cunningham |year=2001 |title=Mitochondrial gene rearrangements confirm the parallel evolution of the crab-like form |journal=Proceedings of the Royal Society B: Biological Sciences |volume=269 |issue=1489 |pages=345–350 |url=http://www.biology.duke.edu/cunningham/pdfs/Morrison%20et%20al.pdf |doi=10.1098/rspb.2001.1886 |pmid=11886621 |pmc=1690904 |access-date=2010-03-26 |archive-date=2010-06-10 |archive-url=https://web.archive.org/web/20100610111946/http://www.biology.duke.edu/cunningham/pdfs/Morrison%20et%20al.pdf |url-status=live }}</ref> 75 px |label2=Anomura |sublabel2=''Late Triassic '' |2={{clade |1={{clade |label1=Porcellanidae |sublabel1=''Late Jurassic'' |1=('''porcelain crabs''')<ref name="Keiler 2014"/> 75 px |2=Munididae (squat lobsters) }} |2={{clade |1={{clade |1=Parapaguridae (deep water sea anemone hermit crabs) |2={{clade |1=Lomisidae ('''hairy stone crabs''')<ref>{{cite journal |author1=Jonas Keiler |author2=Stefan Richter |author3=Christian S. Wirkner |year=2016 |title=Revealing their innermost secrets: an evolutionary perspective on the disparity of the organ systems in anomuran crabs (Crustacea: Decapoda: Anomura) |journal=Contributions to Zoology |volume=85 |issue=4 |pages=361–386 |doi=10.1163/18759866-08504001 |doi-access=free }}</ref> 75 px |2=Aeglidae }} }} |2={{clade |1=Hippidae (mole crabs or sand crabs) 75 px |label2=Paguroidea |sublabel2=''Late Cretaceous'' |2={{clade |label1=Lithodidae |sublabel1=''Late Cenozoic'' |1=('''king crabs''')<ref>{{cite journal |last1=Keiler |first1=Jonas |last2=Richter |first2=Stefan |last3=Wirkner |first3=Christian S. |year=2013 |title=Evolutionary morphology of the hemolymph vascular system in hermit and king crabs (Crustacea: Decapoda: Anomala) |journal=Journal of Morphology |volume=274 |issue=7 |pages=759–778 |doi=10.1002/jmor.20133|pmid=23508935 |bibcode=2013JMorp.274..759K |s2cid=24458262 }}</ref><ref>{{cite journal |last1=Keiler |first1=Jonas |last2=Richter |first2=Stefan |last3=Wirkner |first3=Christian S. |year=2015 |title=The anatomy of the king crab Hapalogaster mertensii Brandt, 1850 (Anomura: Paguroidea: Hapalogastridae) – new insights into the evolutionary transformation of hermit crabs into king crabs |journal=Contributions to Zoology |volume=84 |issue=2 |pages=149–165 |doi=10.1163/18759866-08402004 |doi-access=free }}</ref> 75 px |label2=Paguridae |2={{clade |1=''Birgus latro'' ('''coconut crab''') 75 px |2='''''Patagurus rex'''''<ref>{{cite web |title=Remarkable new true crab-like hermit discovered |url=https://www.floridamuseum.ufl.edu/science/remarkable-new-true-crab-like-hermit-discovered/ |website=Florida Museum |date=13 December 2013 |publisher=University of Florida |access-date=December 9, 2020 |archive-date=October 25, 2020 |archive-url=https://web.archive.org/web/20201025134235/https://www.floridamuseum.ufl.edu/science/remarkable-new-true-crab-like-hermit-discovered/ |url-status=live }}</ref> 75 px |3=(other hermit crabs) 70px }} }} }} }} }} }} }} }} }} }}

==== Specific groups ====

===== Chelicerata =====

Horseshoe crabs (Xiphosura) are an ancient group within the Chelicerata, known from the late Ordovician of Canada, around 445 million years ago.<ref name="Rudkin 2008">{{cite journal |last1=Rudkin |first1=David M. |author2=Young, Graham A. |author3=Nowlan, Godfrey S. |year=2008 |title=The oldest horseshoe crab: a new xiphosurid from Late Ordovician Konservat-Lagerstätten deposits, Manitoba, Canada |journal=Palaeontology |volume=51 |issue=1 |pages=1–9 |doi=10.1111/j.1475-4983.2007.00746.x |doi-access=free |bibcode=2008Palgy..51....1R }}</ref> Their bodies are divided into an anterior prosoma (fused head and thorax) and a posterior opisthosoma, or abdomen. The upper surface of the prosoma is covered by a semicircular carapace (top part of the shell), while the underside bears five pairs of walking legs and a pair of pincer-like chelicerae. The mouth is on the underside of the prosoma, between the bases of the walking legs.<ref>{{cite book |last=Barnes |first=Robert D. |year=1982 |title=Invertebrate Zoology |publisher=Holt-Saunders International |location=Philadelphia |pages=590–595 |isbn=978-0-03-056747-6}}</ref>

===== Decapoda =====

Crab-like decapods span multiple groups:

* True crabs (Brachyura) are generally covered with a thick exoskeleton (jointed shell), composed primarily of highly mineralized chitin.<ref>{{cite journal |last1=Boßelmann |first1=F. |author2=Romano, P. |author3=Fabritius, H. |author4=Raabe, D. |author5=Epple, M. |date=25 October 2007 |title=The composition of the exoskeleton of two crustacea: The American lobster Homarus americanus and the edible crab ''Cancer pagurus'' |journal=Thermochimica Acta |volume=463 |issue=1–2 |pages=65–68 |doi=10.1016/j.tca.2007.07.018|bibcode=2007TcAc..463...65B }}</ref><ref>{{cite journal |last1=Chen |first1=P. |author2=Lin, A. Y. |author3=McKittrick, J. |author4=Meyers, M. A. |date=May 2008 |title=Structure and mechanical properties of crab exoskeletons |journal=Acta Biomaterialia |volume=4 |issue=3 |pages=587–596 |doi=10.1016/j.actbio.2007.12.010 |pmid=18299257 }}</ref> Males often have larger claws than females.<ref>{{cite web |last=Sweat |first=L. H. |url=http://www.sms.si.edu/irLspec/Pachyg_transv.htm |title=''Pachygrapsus transversus'' |publisher=Smithsonian Institution |access-date=20 January 2010 |date=21 August 2009 |archive-date=20 June 2017 |archive-url=https://web.archive.org/web/20170620100625/http://www.sms.si.edu/irLspec/Pachyg_transv.htm |url-status=live }}</ref> * Porcelain crabs (Porcellanidae) are small flattened decapods that hide under rocks. They often shed limbs to escape predators.<ref>{{cite book |first1=Gary C. B. |last1=Poore |first2=Shane T. |last2=Ahyong |year=2004 |title=Marine decapod Crustacea of southern Australia: a guide to identification |publisher=CSIRO Publishing |isbn=978-0-643-06906-0 |chapter=Porcellanidae Haworth, 1825 |pages=242–246 |chapter-url=https://books.google.com/books?id=ZZWnuGc0xlMC&pg=PA242}}</ref> * The hairy stone crab (Lomisidae) is a slow-moving crab of the Australian shore. It is camouflaged with brown hair.<ref>{{cite web |url=http://www.museum.vic.gov.au/crust/mov1711t.html |year=1996 |title=Hairy Stone Crab |publisher=Museum Victoria |access-date=2006-08-15 |archive-url=https://web.archive.org/web/20060411140558/http://www.museum.vic.gov.au/crust/mov1711t.html |archive-date=2006-04-11 |url-status=dead }}</ref> * Hermit crabs (Paguroidea) have heavily armoured crab-like claws, but in place of a carapace, they inhabit empty scavenged gastropod mollusc shells to protect their fragile bodies.<ref>{{cite WoRMS |last1=McLaughlin |first1=Patsy |last2=Türkay |first2=Michael |year=2011 |title=Paguroidea |db=Paguroidea |id=106687 |access-date=25 November 2011}}</ref><ref>{{cite journal |last=Hazlett |first=B. A. |date=1981 |title=The Behavioral Ecology of Hermit Crabs |url=https://www.annualreviews.org/doi/10.1146/annurev.es.12.110181.000245 |journal=Annual Review of Ecology and Systematics |volume=12 |issue=1 |pages=1–22 |doi=10.1146/annurev.es.12.110181.000245 |bibcode=1981AnRES..12....1H |url-access=subscription |archive-date=17 July 2021 |access-date=19 November 2025 |archive-url=https://web.archive.org/web/20210717235616/https://www.annualreviews.org/doi/10.1146/annurev.es.12.110181.000245 |url-status=live }}</ref> * King crabs (Lithodidae) live mainly in cold deep water. They resemble brachyurans but are more closely related to hermit crabs.<ref>{{cite book |last1=Poore |first1=Gary C. B. |last2=Ahyong |first2=Shane T. |author-link2=Shane T. Ahyong |title=Marine Decapod Crustacea: A Guide to Families and Genera of the World |chapter=Anomura |pages=311–317 |publisher=CRC Press |year=2023 |isbn=978-1-4863-1178-1}}</ref> * The coconut crab (''Birgus'') is a large terrestrial hermit crab of islands in the Pacific and Indian oceans.<ref name="Schueman 2025"/> * ''Patagurus rex'' is a specialised hermit crab from Polynesia, living at a depth of 400 metres. Its carapace is unique but enough to make it look crab-like.<ref name="Anker 2013">{{cite journal |last1=Anker |first1=Arthur |last2=Paulay |first2=Gustav |title=A remarkable new crab-like hermit crab (Decapoda: Paguridae) from French Polynesia, with comments on carcinization in the Anomura |journal=Zootaxa |date=22 October 2013 |volume=3722 |issue=2 |doi=10.11646/zootaxa.3722.2.9 }}</ref>

=== Size and shape ===

Crabs vary in size from the pea crab, a few millimeters wide,<ref name="Baker 2023">{{cite web |last1=Baker |first1=Nick |title=Pea crabs guide: what they are and their lifecycle |url=https://www.discoverwildlife.com/animal-facts/insects-invertebrates/pea-crabs-guide |website=Discover Wildlife |access-date=4 November 2025 |date=1 February 2023}}</ref> to the Japanese spider crab, with a leg span up to {{convert|4|m|ft|abbr=on}}.<ref>{{cite web |url=http://na.oceana.org/en/explore/creatures/japanese-spider-crab |title=Japanese spider crab ''Macrocheira kaempferi'' |publisher=Oceana North America |access-date=2009-01-02 |archive-url=https://web.archive.org/web/20091114041143/http://na.oceana.org/en/explore/creatures/japanese-spider-crab |archive-date=2009-11-14 }}</ref> The coconut crab is the largest terrestrial arthropod, and indeed the largest extant terrestrial invertebrate, at up to {{convert|40|cm|in|0|abbr=on}} long and weighing up to {{convert|4.1|kg|lb|frac=4|abbr=on}}.<ref name="Schueman 2025">{{cite web |last=Schueman |first=Lindsey Jean |title=Inside the world of coconut crabs: The largest land arthropod |url=https://www.oneearth.org/species-of-the-week-coconut-crab/ |website=One Earth |access-date=5 November 2025 |date=6 October 2025}}</ref>

<gallery class=center mode=nolines widths=180 heights=180 caption="Smallest and largest"> File:Crabe petit pois (Pinnotheres pisum) dans les aquariums de mareis.jpg|Adult pea crab, one of the smallest species, a few millimetres across<ref name="Baker 2023"/> File:Birgus latro 171058756 (cropped).jpg|Coconut crab, the largest terrestrial arthropod, weighing up to {{convert|4.1|kg|lb|frac=4|abbr=on}} File:Macrocheira kaempferi.jpg|Japanese spider crab, with a leg span of as much as {{convert|4|m|ft|abbr=on}} </gallery>

=== Feeding methods ===

Many crabs are free-living marine omnivores, feeding on a mixture of algae, small animals such as molluscs, polychaete worms, other crustaceans, and detritus.<ref name="Chartosia 2010"/> Others are more specialised: the mottled crab ''Grapsus albolineatus'', for example, is herbivorous, feeding mainly on algae and preferring the more nutritious filamentous algae to leafy (foliose) algae,<ref>{{cite journal |last1=Kennish |first1=R |last2=Williams |first2=G. A. |date=1997 |title=Feeding preferences of the herbivorous crab Grapsus albolineatus: the differential influence of algal nutrient content and morphology |url=http://hub.hku.hk/handle/10722/57250 |journal=Marine Ecology Progress Series |volume=147 |pages=87–95 |doi=10.3354/meps147087 |bibcode=1997MEPS..147...87K |doi-access=free |url-access=subscription }}</ref> while the yellow moon crab ''Ashtoret lunaris'' is carnivorous.<ref name="Yamada 2013">{{cite journal |last1=Yamada |first1=Hideaki |last2=Kobayashi |first2=Masato |last3=Sato |first3=Taku |last4=Kawabata |first4=Yuuki |title=Effects of artificial seaweed and water depth on vulnerability of juvenile black-spot tuskfish Choerodon schoenleinii to carnivorous crab Ashtoret lunaris |journal=Nippon Suisan Gakkaishi |volume=79 |issue=5 |date=2013 |issn=0021-5392 |doi=10.2331/suisan.79.797 |doi-access=free |pages=797–803 |url=https://www.jstage.jst.go.jp/article/suisan/79/5/79_13-00023/_pdf |access-date=4 November 2025}}</ref> The porcelain crabs are plankton feeders, filtering their prey from seawater using long feathery bristles on their mouthparts.<ref name=Allen>{{cite book |first=Gerald R. |last=Allen |year=1997 |title=Tropical Marine Life |series=Periplus Nature Guides |publisher=Tuttle Publishing |isbn=978-962-593-157-9 |chapter=Anemone crab ''Neopetrolisthes maculatus'' |page=35 |chapter-url=https://books.google.com/books?id=vpMSjJ5DVDYC&pg=PA35}}</ref> The tiny soft-bodied oyster crab is a kleptoparasite of oysters, living inside the host's shell and eating its food.<ref name="Walters 2024">{{cite journal |last1=Walters |first1=Linda J. |last2=Busch |first2=Sidney J. |last3=Vermeulen |first3=Sophia |last4=Craig |first4=Casey A. |title=Entanglement and ingestion of microfibers by the oyster pea crab Zaops ostreum, an endosymbiont of the eastern oyster Crassostrea virginica |journal=Marine Pollution Bulletin |volume=201 |date=2024 |doi=10.1016/j.marpolbul.2024.116251 |article-number=116251 |pmid=38479324 |bibcode=2024MarPB.20116251W |url=https://linkinghub.elsevier.com/retrieve/pii/S0025326X24002285|url-access=subscription }}</ref>

<gallery class=center mode=nolines widths=180 heights=130 caption="Diverse feeding methods"> File:Grapsus albolineatus in natural environment. Eriyadu, Maldives.jpg|The mottled lightfoot crab is herbivorous. File:Ashtoret lunaris (cropped).jpg|The yellow moon crab is carnivorous. File:Porcellana platycheles millport (mouthparts detail).jpg|Porcelain crabs are filter feeders, using feathery bristles on their mouthparts. </gallery>

=== Ecological niches ===

The tufted ghost crab ''Ocypode cursor'' is semi-terrestrial, consuming terrestrial animals such as insects.<ref name="Chartosia 2010">{{cite journal |last1=Chartosia |first1=Niki |title=Diet Composition of Five Species of Crabs (Decapoda, Brachyura) that Show a Gradual Transition from Marine to Terrestrial Life |journal=Crustaceana |date=2010 |volume=83 |issue=10 |pages=1181–1197 |doi=10.1163/001121610X533502 |jstor=41038629 |bibcode=2010Crust..83.1181C |url=https://www.researchgate.net/publication/261934839}}</ref> Other species, including the pea crabs (Pinnotheridae), are parasitic, living inside hosts such as bivalve molluscs.<ref name="Baker 2023"/> The tree crab or Caribbean hermit crab is terrestrial as an adult,<ref name="Farrelly 2005"/> only returning to the ocean to spawn.<ref name="Nieves 2003">{{cite journal |first1=Ángel M. |last1=Nieves-Rivera |author2=Ernest H. Williams, Jr. |s2cid=53587978 |year=2003 |title=Annual migrations and spawning of ''Coenobita clypeatus'' (Herbst) on Mona Island (Puerto Rico) and notes on inland crustaceans |journal=Crustaceana |volume=76 |issue=5 |pages=547–558 |doi=10.1163/156854003322316191 |jstor=20105594 |bibcode=2003Crust..76..547W }}</ref> It feeds on plants and by scavenging,<ref>{{cite journal |last1=Linton |first1=Stuart |last2=Greenaway |first2=Peter |title=A review of feeding and nutrition of herbivorous land crabs: adaptations to low quality plant diets |journal=Journal of Comparative Physiology B |date=6 February 2007 |volume=177 |issue=3 |pages=269–286 |doi=10.1007/s00360-006-0138-z |pmid=17279390 |s2cid=23721149 |url=https://figshare.com/articles/journal_contribution/20818345 }}</ref> and like other hermit crabs, takes over a mollusc shell for protection, breathing air with a lung.<ref name="Farrelly 2005">{{cite journal |last1=Farrelly |first1=C.A. |last2=Greenaway |first2=P. |title=The morphology and vasculature of the respiratory organs of terrestrial hermit crabs (Coenobita and Birgus): gills, branchiostegal lungs and abdominal lungs |journal=Arthropod Structure & Development |date=January 2005 |volume=34 |issue=1 |pages=63–87 |doi=10.1016/j.asd.2004.11.002 |bibcode=2005ArtSD..34...63F }}</ref> Some 1,300 species of crabs in 8 families are adapted to freshwater.<ref name="Yeo">{{cite journal |first1=Darren C. J. |last1=Yeo |author2=Peter K. L. Ng |author3=Neil Cumberlidge |author4=Célio Magalhães |author5=Savel R. Daniels |author6=Martha R. Campos |year=2008 |title=Global diversity of crabs (Crustacea: Decapoda: Brachyura) in freshwater |journal=Hydrobiologia |volume=595 |issue=1 |pages=275–286 |doi=10.1007/s10750-007-9023-3 |series=Developments in Hydrobiology, vol. 198 |editor1=E. V. Balian |editor2=C. Lévêque |editor3=H. Segers |editor4=K. Martens |publisher=Springer |bibcode=2008HyBio.595..275Y |isbn=978-1-4020-8258-0 |url=http://scholarbank.nus.edu.sg/handle/10635/102459 }}</ref> Christmas Island red crabs make an annual mass migration to the sea to lay their eggs.<ref name="Red Crabs">{{cite web |date=1 December 2013 |title=Red crabs – video footage of the migration |publisher=Parks Australia |url=http://www.parksaustralia.gov.au/christmas/people-place/red-crabs.html |access-date=3 December 2013 |archive-date=3 July 2014 |archive-url=https://web.archive.org/web/20140703153052/http://parksaustralia.gov.au/christmas/people-place/red-crabs.html |url-status=dead }}</ref>

<gallery class=center mode=nolines widths=200 heights=130 caption="Diverse ecological niches"> File:Zaops ostreum.jpg|The oyster crab<br/>(centre, orange-coloured) is a kleptoparasite of oysters. File:Caribbean hermit crab.JPG|The Caribbean hermit crab is mainly terrestrial. File:Freshwater crab (Potamon potamios) Nazilli.jpg|Among many species of freshwater crab, ''Potamon potamios'' lives in or near rivers. File:Christmas Island Crabs on annual migration (cropped).JPG|Christmas Island red crabs on their annual migration to the sea </gallery>

== Similarity of body plan through carcinisation ==

Most crabs are members of the Brachyura, sometimes called "true crabs", with around 7,000 species.<ref name="Martin & Davis">{{cite book |url=http://atiniui.nhm.org/pdfs/3839/3839.pdf |title=An Updated Classification of the Recent Crustacea |author1=Joel W. Martin |author2=George E. Davis |year=2001 |page=132 |publisher=Natural History Museum of Los Angeles County |access-date=2009-12-14 |archive-date=2013-05-12 |archive-url=https://web.archive.org/web/20130512091254/http://atiniui.nhm.org/pdfs/3839/3839.pdf }}</ref> Several other groups of decapod crustaceans among the Anomura, such as king crabs and porcelain crabs, have a similar appearance; all have convergently evolved through the process of carcinisation to the crab body form and way of life. Crabs are thus not a single taxonomic group or clade, but are polyphyletic.<ref>{{cite journal |last=Borradaile |first=Lancelot Alexander |author-link=Lancelot Alexander Borradaile |title=Crustacea. Part II. Porcellanopagurus: an instance of carcinization |journal=British Antarctic ("Terra Nova") Expedition, 1910. Natural History Report. Zoology |year=1916 |volume=3 |number=3 |pages=111–126}}</ref><ref>{{cite journal |last1=Martin |first1=J. W. |last2=Abele |first2=L. G. |title=Phylogenetic relationships of the genus ''Aegla'' (Decapoda: Anomura: Aeglidae), with comments on anomuran phylogeny |journal=Journal of Crustacean Biology |year=1986 |volume=6 |number=3 |pages=576–612 |doi= 10.1163/193724086X00406 |bibcode=1986JCBio...6..576. }}</ref><ref>{{cite journal |last1=McLaughlin |first1=P. A. |last2=Lemaitre |first2=R. |title=Carcinization in the Anomura - fact or fiction? I. Evidence from adult morphology |journal=Contributions to Zoology |year=1997 |volume=67 |number=2 |pages=79–123 |doi=10.1163/18759866-06702001 |doi-access=free}}</ref><ref>{{cite journal |last=Scholtz |first=G. |title=Evolution of crabs - history and deconstruction of a prime example of convergence |journal=Contributions to Zoology |year=2014 |volume=83 |number=2 |pages=87–105 |doi=10.1163/18759866-08302001 |doi-access=free}}</ref> Many crabs can run swiftly sideways ("crabwise"), though others walk forwards,<ref name="Sleinis 1980">{{cite journal |title=Locomotion in a forward walking crab |first1=Sally |last1=Sleinis |first2=Gerald E. |last2=Silvey |journal=Journal of Comparative Physiology A |volume=136 |issue=4 |year=1980 |doi=10.1007/BF00657350 |pages=301–312 |s2cid=33455459 }}</ref> and some can swim.<ref name="Hazerli 2020">{{cite journal |last1=Hazerli |first1=Dennis |last2=Richter |first2=Stefan |title=Why "swimming crabs" are able to swim – The importance of the axial skeleton: A comparison between the "swimming crab" Liocarcinus depurator and two other brachyuran crabs (Cancer pagurus, Carcinus maenas) using μCT and 3D-reconstruction |journal=Arthropod Structure & Development |volume=59 |date=2020 |doi=10.1016/j.asd.2020.100972 |article-number=100972 |pmid=33039754 |bibcode=2020ArtSD..5900972H }}</ref>

The carcinised body form is defined by Keiler and colleagues (2014) as having the following attributes:<ref name="Keiler 2014"/>

* "The carapace is flatter than it is broad and possesses lateral margins." * "The sternites are fused into a wide sternal plastron which possesses a distinct emargination on its posterior margin." * "The pleon is flattened and strongly bent, in dorsal view completely hiding the tergites of the fourth pleonal segment, and partially or completely covers the plastron."

[[File:Crab vs lobster body plan.svg|thumb|center|upright=2.5|Crab body plan, its adaptations illustrated by comparison with a lobster (undersides shown) ]]

== Interactions with humans ==

=== Fisheries and food ===

Crabs make up some 20% of all marine crustaceans caught, farmed, and consumed worldwide, amounting to 1.5 million tonnes annually. One species, the Asian blue crab ''Portunus trituberculatus'', accounts for one-fifth of that total. Other commercially important taxa include ''Portunus pelagicus'', several species in the genus ''Chionoecetes'', the blue crab (''Callinectes sapidus''), ''Charybdis'' spp., ''Cancer pagurus'', the Dungeness crab (''Metacarcinus magister''), and ''Scylla serrata'', each of which yields more than 20,000 tonnes annually.<ref>{{cite web |title=Global Capture Production 1950–2004 |url=http://www.fao.org/figis/servlet/TabLandArea?tb_ds=Capture&tb_mode=TABLE&tb_act=SELECT&tb_grp=COUNTRY |archive-url=https://web.archive.org/web/20160123085332/http://www.fao.org/figis/servlet/TabLandArea?tb_ds=Capture&tb_mode=TABLE&tb_act=SELECT&tb_grp=COUNTRY |archive-date=23 January 2016 |access-date=26 August 2006 |publisher=Food and Agriculture Organization}}</ref>

<gallery class=center mode=nolines widths=190 heights=140 caption="Crab fisheries"> File:Untitled - panoramio - karlee ladyk (11).jpg|Small-scale crab fishing File:King crab pots.jpg|Commercial king crab traps, awaiting the crabbing season File:Crab fishing boat.png|Crab boat in the Bering Sea File:Catching crabs.jpg|Hauling in a crab trap </gallery>

In Western Europe, much of the crab meat is from the brown crab ''Cancer pagurus'', noted for its sweet, delicate flavour. The United Kingdom hosts significant fisheries of this species, with major operations in Scotland and the South West of England.<ref>{{cite web |publisher=Nautilus Consultants |date=2009 |title=Future Management of Brown Crab in the UK and Ireland (IPF_D123) |url=http://www.seafish.org/media/Publications/SR633_NautilusBrownCrabManagement_D123_Final.pdf |website=www.seafish.org |archive-url=https://web.archive.org/web/20110906174800/https://www.seafish.org/media/Publications/SR633_NautilusBrownCrabManagement_D123_Final.pdf |archive-date=6 September 2011 }}</ref> Dressed crab is a traditional seafood meal in British cuisine made of the meat of the brown crab served in its own shell.<ref>{{cite web |title=How to dress a crab |url=https://www.bbc.co.uk/food/recipes/dressedcrab_90206 |publisher=BBC |access-date=24 September 2023}}</ref>

In North America, there are commercial fisheries for the blue crab ''Callinectes sapidus'' along the Atlantic coast of the United States, and in the Gulf of Mexico. The fishery was centered on the Chesapeake Bay, but other places are increasing in importance.<ref name="Cascorbi">{{cite web |first=Alice |last=Cascorbi |date=February 14, 2004 |title=Seafood Report: Blue Crab, ''Callinectes sapidus'' |work=Seafood Watch |publisher=Monterey Bay Aquarium |url=http://www.montereybayaquarium.org/cr/cr_seafoodwatch/content/media/MBA_SeafoodWatch_BlueCrabReport.pdf |access-date=September 12, 2012 |archive-url=https://web.archive.org/web/20130728194105/http://www.montereybayaquarium.org/cr/cr_seafoodwatch/content/media/MBA_SeafoodWatch_BlueCrabReport.pdf |archive-date=2013-07-28 }}</ref> Crab cakes are traditionally made from Chesapeake Bay crabs.<ref>{{cite book |url=https://books.google.com/books?id=hs3z0zZWxpYC&pg=PA81 | title=500 Things to Eat Before It's Too Late: and the Very Best Places to Eat Them |publisher=Houghton Mifflin Harcourt |last=Stern |first=Jane |date=4 June 2009 |page=81 |isbn=978-0-547-41644-1 }}</ref><ref>{{cite web |title=The History of Maryland Crab Cakes - Brookside Inn Restaurant - Oxford |url=https://nearsay.com/c/732124/272370/the-history-of-maryland-crab-cakes|website=nearsay.com |access-date=12 May 2020 |archive-url=https://web.archive.org/web/20221027123845/https://connect2local.com/l/272370/c/732124/the-history-of-maryland-crab-cakes |archive-date=27 October 2022 }}</ref>

In Goa and Mozambique, crab curry is a typical dish, flavoured with chilis, garlic, coconut, and spices.<ref>{{cite web |url=http://www.receitasemenus.net/caril-caranguejo-mocambique/|title=Caril de Caranguejo (Moçambique) - ReceitaseMenus.net |first=Luis |last=Ferreira |website=Receitasemenus.net |access-date=10 September 2017}}</ref>

In Ishikawa prefecture, Japan, both the meat and the eggs of the snow crab are served as sushi in wintertime. The male is known as ''kano-gani'', the female as ''kobako-gani''. The short fishing season for the females makes ''kobako-gani'' sushi a rare delicacy.<ref>{{cite magazine |last=Osamu |first=Sawaji |title=Ishikawa Wintertime Sushi |magazine=Highlighting Japan |date=February 2023 |url=https://www.gov-online.go.jp/pdf/hlj/20230201/hlj202302_20-21_Ishikawa_Wintertime_Sushi.pdf |access-date=6 November 2025 |pages=20–21}}</ref>

<gallery class=center mode=nolines widths=190 heights=140 caption="Dishes made with crab"> File:Crab meat in shell with salad and Marie Rose sauce.jpg|Dressed crab with salad<br/>and Marie Rose sauce File:Bartley's.jpg|Crab cakes with sweet potato fries, coleslaw, and tartar sauce File:Caril_de_caranguejo.jpg|Goan style crab curry File:Kobako crab sushi (32301286552).jpg|''Kobako-gani'' sushi with snow crab meat and eggs </gallery>

=== In culture ===

Both the constellation Cancer and the astrological sign Cancer are named after the crab, and depicted as such.<ref>{{cite book |first=B. B. |last=Rossi |year=1969 |title=The Crab Nebula: Ancient History and Recent Discoveries |publisher=Center for Space Research, Massachusetts Institute of Technology |id=CSR-P-69-27 |url=https://ntrs.nasa.gov/search.jsp?R=19700008151}}</ref> In Greek mythology, ''Karkinos'' was a crab that came to the aid of the Lernaean Hydra as it battled the hero Heracles.<ref>{{Cite book |last=Barreiro |first=Rafael Fontán |url=https://books.google.com/books?id=8gzRgDCh9NkC&pg=PA107 |title=Diccionario de la mitología |date=2007-05-16 |publisher=EDAF |isbn=978-84-414-0397-0 |language=es}}</ref> The crab is at best a secondary character in the myth, and sometimes omitted altogether. This has been explained by the suggestion that it was introduced into the myth by Mesopotamian influence, as astrologers tried to associate the Labours of Hercules with the twelve signs of the Zodiac.<ref>{{Cite web |title=AAGC – Cancer |url=http://www.astrosurf.com/aagc/gt_historia_constelaciones/cancer.htm |access-date=2022-04-18 |website=www.astrosurf.com}}</ref><ref name="Graves 2017">{{cite book |last=Graves |first=Robert |url=https://books.google.com/books?id=R9k1DwAAQBAJ&q=the%20greek%20myths%20robert%20graves |chapter=The Labours of Hercules |title=The Greek Myths: The Complete and Definitive Edition |date=2017 |orig-year=1958 |publisher=Penguin Books |isbn=978-0-241-98338-6}}</ref>

<gallery class=center mode=nolines widths=180 heights=180 caption="Mythology and astrology"> File:Lernaean Hydra Louvre CA598 n2.jpg|The crab ''Karkinos'' attacking Herakles as he fights the Lernaean Hydra. Attic lekythos pot, "the Diosphos Painter",<br/>500–475 BC File:Sidney Hall - Urania's Mirror - Cancer.jpg|The constellation of Cancer, the crab, from Urania's Mirror,<br/>c. 1825 </gallery>

Crabs have appeared in art since ancient times in many different media. The Moche people of ancient Peru worshipped nature, especially the sea,<ref>{{cite book |first=Elizabeth |last=Benson |title=The Mochica: A Culture of Peru |location=New York |publisher=Praeger Press |year=1972 |isbn=978-0-500-72001-1}}</ref> and often depicted crabs in their art.<ref>{{cite book |first=Katherine |last=Berrin |title=The Spirit of Ancient Peru: Treasures from the Museo Arqueológico Rafael Larco Herrera |location=New York |publisher=Thames and Hudson |year=1997 |page=216 |isbn=978-0-500-01802-6}}</ref> Among the many later representations, the German artist Albrecht Dürer made a meticulous painting of the crab ''Eriphia verrucosa'' in 1495; since the species lives on the Adriatic coast, he likely painted the animal when he visited Venice.<ref>{{cite web |title=Crab (Eriphia Spinifrons) |url=https://www.boijmans.nl/en/collection/artworks/78054/crab-eriphia-spinifrons |publisher=Museum Boijmans Van Beuningen |access-date=19 November 2025}}</ref> Quite a different artistic portrayal is the monumental crab table setting charger created by the Barbizet Studio that made glazed earthenware pottery between 1850 and 1890.<ref>{{cite web |title=Charger |url=https://cincinnatiartmuseum.org/art/explore-the-collection?id=11295884 |publisher=Cincinnati Art Museum |access-date=19 November 2025}}</ref> In China, Gao Qipei (1672–1734) painted ''Crabs and Chrysanthemums'' in ink and light watercolour on paper.<ref>{{cite web |title=Crabs and Chrysanthemums: Gao Qipei |url=https://www.brooklynmuseum.org/objects/110409 |publisher=Brooklyn Museum |access-date=19 November 2025}}</ref> In Panama, the Guna people of the San Blas Islands make Mola appliqué blouse panels decorated with motifs such as crabs from the waters of the Caribbean.<ref>{{cite web |last1=Vazquez de Arthur |first1=Andrea |title=Fashioning Identity: Mola Textiles of Panamá |url=https://www.clevelandart.org/articles/fashioning-identity-mola-textiles-panama |publisher=Cleveland Museum of Art |access-date=19 November 2025 |date=8 October 2020}}</ref>

<gallery class=center mode=nolines widths=180 heights=180 caption="In different media through the centuries">  File:Albrecht Dürer 108.jpg|Crab by Albrecht Dürer, gouache and watercolour on paper, Germany, 1495 File:Brooklyn Museum - Crabs and Chrysanthemums - Gao Qipei.jpg|''Crabs and Chrysanthemums'', Gao Qipei, ink and light colour on paper, China, 18th century File:Charger attributed to the Barbizet Studio, c. 1850, Cincinnati Art Museum.jpg|Charger attributed to the Barbizet Studio, glazed earthenware, c. 1850  File:Crab in Mola (blouse panel), Cuna (Kuna) Indians, Honolulu Museum of Art, 3740.1 (cropped).JPG|''Mola'' appliqué blouse panel, Nulanega Island, Panama, 20th century </gallery>

One of Rudyard Kipling's ''Just So Stories'', "The Crab that Played with the Sea", tells the story of a gigantic crab who made the waters of the sea go up and down like the tides.<ref>{{cite book |last=Kipling |first=Rudyard |author-link=Rudyard Kipling |title=Just So Stories |title-link=Just So Stories |date=1902 |publisher=Macmillan |chapter=The Crab that Played with the Sea |chapter-url=http://etc.usf.edu/lit2go/79/just-so-stories/1297/the-crab-that-played-with-the-sea/}}</ref> The paleontologist Richard Fortey has identified Kipling's giant crab as a horseshoe crab.<ref>{{cite web |title=Just So Science: The Crab that Played with the Sea |url=https://www.bbc.co.uk/programmes/b04795tq |publisher=BBC |access-date=6 November 2025}}</ref> In Malay mythology, ocean tides were believed to be caused by water rushing in and out of a hole in the Navel of the Seas (''Pusat Tasek''), where "there sits a gigantic crab which twice a day gets out in order to search for food".<ref>{{cite book |title=Malay Magic |last=Skeat |first=Walter William |author-link=Walter William Skeat (anthropologist) |publisher=Macmillan |year=1900 |location=London |pages=1–15 |chapter=Chapter 1: Nature |chapter-url=https://www.gutenberg.org/files/47873/47873-h/47873-h.htm#s1.2}}</ref>

[[File:Just so stories for litle children (1902) (14761888306).jpg|thumb|center|upright|Illustration for "The Crab that Played with the Sea" (in ''Just So Stories''), Rudyard Kipling, 1902]]

=== As pets ===

Hermit crabs are commonly kept as pets and used in the marine aquarium trade.<ref name="Bracken-Grissom 2013"/> A popular species is the Caribbean hermit crab, ''Coenobita clypeatus''. They can live for 30 years in captivity if their requirements, including simulating a coastal rainforest, are met. The size of tank must be substantial. There must be a substrate of sand and coconut fibre that they can dig in to facilitate moulting. The temperature and humidity of the air must be controlled. A pool of fresh water and a pool of correctly formulated salt water are both necessary.<ref name="Sinclair 2025">{{cite web |last=Sinclair |first=Melissa Scott |title=It's the Most Misunderstood Pet in America. If Only You Knew Where It Came From—and What It's Capable Of. |website=Slate Magazine |date=19 August 2025 |url=https://slate.com/technology/2025/08/hermit-crab-lifespan-beach-pet-cage-breeding.html |access-date=6 November 2025}}</ref>

[[File:Pet hermit crabs (cropped).jpg|thumb|center|upright=0.9|Hermit crabs in an aquarium]]

=== Meme ===

The zoologist Joanna Wolfe, writing in ''Scientific American'', notes a popular meme which jokes that crabs are the "ultimate forms"<ref name="Wolfe 2025"/> of life as "everything will eventually evolve into a crab".<ref name="Wolfe 2025"/> Sara Kiley Watson, writing in ''Popular Science'', comments that the joke "comes from an actual truth", that decapods span multiple crab-like groups, including the true crabs but not limited to them.<ref name="Watson 2020">{{cite web |last=Watson |first=Sara Kiley |title=Why everything eventually becomes a crab |url=https://www.popsci.com/story/animals/why-everything-becomes-crab-meme-carcinization/ |publisher=Popular Science |access-date=19 November 2025 |date=14 December 2020}}</ref> Wolfe explains that the meme parodies the genuine process of carcinisation which has taken place in at least five different groups of decapods, but that the process does not apply to humans or other animals.<ref name="Wolfe 2025">{{cite magazine |last=Wolfe |first=Joanna |title=Crab Memes Amplify Mistaken Ideas about Evolution |magazine=Scientific American |date=27 February 2025 |url=https://www.scientificamerican.com/article/crab-memes-amplify-mistaken-ideas-about-evolution/ |access-date=5 November 2025 |archive-date=27 February 2025 |archive-url=https://web.archive.org/web/20250227231154/https://www.scientificamerican.com/article/crab-memes-amplify-mistaken-ideas-about-evolution/ |url-status=live }}</ref> The evolutionary palaeobiologist Matthew Wills comments that all the crabs are decapods, and the evolutionary pressures apply in a marine environment where defence, living in crevices, and being wave-swept favour armoured protection, a broad compact body, and the ability to scuttle sideways.<ref name="Swallow 2025">{{cite news |last=Swallow |first=Bea |title=Why does evolution keep creating 'imposter crabs'? |url=https://www.bbc.co.uk/news/articles/cly7d7erz80o |access-date=17 October 2025 |work=BBC News |date=17 October 2025 |archive-date=2 March 2026 |archive-url=https://web.archive.org/web/20260302172542/https://www.bbc.co.uk/news/articles/cly7d7erz80o |url-status=live }}</ref>

[[File:Purple rock crabs (Leptograpsus variegatus) lurking in a crevice under Lion Rock.jpg|thumb|center|upright=1.4|Decapods have repeatedly evolved a crablike body form under the pressures of predation and wave action. A broad low body, an armoured carapace, and the ability to scuttle sideways into a rock crevice all work well in a marine environment. This does not mean that all animals will evolve the same adaptations, as the crab meme wrongly suggests.<ref name="Swallow 2025"/>]]

== References ==

Category:Crabs Category:Arthropod common names Category:Chelicerata Category:Convergent evolution Category:Decapods Category:Polyphyletic groups