Editing Crab (section)

==Classification==
The [[infraorder]] Brachyura contains approximately 7,000 species in 98 [[family (biology)|families]],<ref name="Ling"/><ref name="Ng"/> as many as the remainder of the [[Decapoda]].<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 |pages=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 |url-status=dead }}</ref> The evolution of crabs is characterized by an increasingly robust body, and a reduction in the [[Abdomen#Arthropoda|abdomen]]. Although many other groups have undergone similar processes, [[carcinisation]] is most advanced in crabs. The [[telson]] is no longer functional in crabs, and the [[uropod]]s are absent, having probably evolved into small devices for holding the reduced abdomen tight against the [[Sternum (arthropod)|sternum]].

In most decapods, the [[gonopore]]s (sexual openings) are found on the legs. Since crabs use their first two pairs of [[pleopod]]s (abdominal appendages) for sperm transfer, this arrangement has changed. As the male abdomen evolved into a slimmer shape, the gonopores have moved toward the midline, away from the legs, and onto the sternum.<ref>{{cite journal |author=M. de Saint Laurent |year=1980 |title=Sur la classification et la phylogénie des Crustacés Décapodes Brachyoures. II. Heterotremata et Thoracotremata Guinot, 1977 |journal=[[Comptes rendus de l'Académie des sciences]] |volume=t. 290 |pages=1317–1320}}</ref> A similar change occurred, independently, with the female gonopores. The movement of the female gonopore to the sternum defines the [[clade]] [[Eubrachyura]], and the later change in the position of the male gonopore defines the [[Thoracotremata]]. It is still a subject of debate whether a [[Monophyly|monophyletic group]] is formed by those crabs where the female, but not male, gonopores are situated on the sternum.<ref name="Martin & Davis"/>

===Families===
Numbers of extant and extinct (†) species are given in brackets.<ref name="DeGrave"/> The superfamily [[Eocarcinoidea]], containing ''[[Eocarcinus]]'' and ''[[Platykotta]]'', was formerly thought to contain the oldest crabs; it is now considered part of the [[Anomura]].<ref name="Chablais">{{cite journal |author1=Jérôme Chablais |author2=Rodney M. Feldmann |author3=Carrie E. Schweitzer |year=2011 |title=A new Triassic decapod, ''Platykotta akaina'', from the Arabian shelf of the northern United Arab Emirates: earliest occurrence of the Anomura |journal=[[Paläontologische Zeitschrift]] |volume=85 |issue=1 |pages=93–102 |doi=10.1007/s12542-010-0080-y |bibcode=2011PalZ...85...93C |s2cid=5612385 |url=http://decapoda.nhm.org/pdfs/31744/31744.pdf |archive-url=https://web.archive.org/web/20120319132343/http://decapoda.nhm.org/pdfs/31744/31744.pdf |archive-date=2012-03-19 |url-status=live }}</ref>
{{Multiple image
| direction = vertical
| align = right
| width = 220
| header = Examples of different crab sections
| image1 = Dromia personata.jpg
| caption1 = ''[[Dromia personata]]'' ([[Dromiacea]]: [[Dromiidae]])
| image2 = Ranina ranina.jpg
| caption2 = ''[[Ranina ranina]]'' ([[Raninoida]]: [[Raninidae]])
| image3 = Corystes cassivelaunus.jpg
| caption3 = ''[[Corystes cassivelaunus]]'' ([[Heterotremata]]: [[Corystidae]])
| image4 = Ocypode quadrata.jpg
| caption4 = ''[[Ocypode quadrata]]'' ([[Thoracotremata]]: [[Ocypodidae]])
| image5 = Goneplax rhomboides 2.jpg
| caption5 = ''[[Goneplax rhomboides]]''
}}
* '''Section †[[Callichimaeroida]]'''
** †[[Callichimaeroidea]] (1†)<ref>{{cite journal |last1=Luque |first1=J. |last2=Feldmann |first2=R. M. |last3=Vernygora |first3=O. |last4=Schweitzer |first4=C. E. |last5=Cameron |first5=C. B. |last6=Kerr |first6=K. A. |last7=Vega |first7=F. J. |last8=Duque |first8=A. |last9=Strange |first9=M. |last10=Palmer |first10=A. R. |last11=Jaramillo |first11=C. |title=Exceptional preservation of mid-Cretaceous marine arthropods and the evolution of novel forms via heterochrony |journal=Science Advances |date=24 April 2019 |volume=5 |issue=4 |pages=eaav3875 |doi=10.1126/sciadv.aav3875|pmid=31032408 |pmc=6482010 |bibcode=2019SciA....5.3875L }}</ref>
* '''Section [[Dromiacea]]'''
** †[[Dakoticancroidea]] (6†)
** [[Dromioidea]] (147, 85†)
** [[Glaessneropsoidea]] (45†)
** [[Homolodromioidea]] (24, 107†)
** [[Homoloidea]] (73, 49†)
* '''Section [[Raninoida]]''' (46, 196†)
* '''Section [[Cyclodorippoida]]''' (99, 27†)
* '''Section [[Eubrachyura]]'''
** '''Subsection [[Heterotremata]]'''
*** [[Aethroidea]] (37, 44†)
*** [[Bellioidea]] (7)
*** [[Bythograeoidea]] (14)
*** [[Calappoidea]] (101, 71†)
*** [[Cancroidea]] (57, 81†)
*** [[Carpilioidea]] (4, 104†)
*** [[Cheiragonoidea]] (3, 13†)
*** [[Corystoidea]] (10, 5†)
*** †[[Componocancroidea]] (1†)
*** [[Dairoidea]] (4, 8†)
*** [[Dorippoidea]] (101, 73†)
*** [[Eriphioidea]] (67, 14†)
*** [[Gecarcinucoidea]] (349)
*** [[Goneplacoidea]] (182, 94†)
*** [[Hexapodoidea]] (21, 25†)
*** [[Leucosioidea]] (488, 113†)
*** [[Majoidea]] (980, 89†)
*** [[Orithyioidea]] (1)
*** [[Palicoidea]] (63, 6†)
*** [[Parthenopoidea]] (144, 36†)
*** [[Pilumnoidea]] (405, 47†)
*** [[Portunoidea]] (455, 200†)
*** [[Potamoidea]] (662, 8†)
*** [[Pseudothelphusoidea]] (276)
*** [[Pseudozioidea]] (22, 6†)
*** [[Retroplumoidea]] (10, 27†)
*** [[Trapezioidea]] (58, 10†)
*** [[Trichodactyloidea]] (50)
*** [[Xanthoidea]] (736, 134†) <ref name="Mendoza2022">{{cite journal |title=A comprehensive molecular phylogeny of the brachyuran crab superfamily Xanthoidea provides novel insights into its systematics and evolutionary history |author1=Jose C.E. Mendoza |author2=Kin Onn Chan |author3= Joelle C.Y. Lai |author4=Brent P. Thoma |author5=Paul F. Clark |author6=Danièle Guinot |author7=Darryl L. Felder |author8=Peter K.L. Ng |journal=[[Molecular Phylogenetics and Evolution]] |volume=177 |year=2022 |pages=107627 |doi=10.1016/j.ympev.2022.107627 |pmid=36096461 |doi-access=free|bibcode=2022MolPE.17707627M }}</ref>
** '''Subsection [[Thoracotremata]]''' <ref name="Tsang2022">{{cite journal |title=Molecular phylogeny of Thoracotremata crabs (Decapoda, Brachyura): Toward adopting monophyletic superfamilies, invasion history into terrestrial habitats and multiple origins of symbiosis |author1=Chandler T.T. Tsang |author2=Christoph D. Schubart |author3=Ka Hou Chu |author4=Peter K.L. Ng |author5=Ling Ming Tsang |journal=[[Molecular Phylogenetics and Evolution]] |volume=177 |year=2022 |pages=107596 |doi=10.1016/j.ympev.2022.107596 |pmid=35914646 |doi-access=free|bibcode=2022MolPE.17707596T }}</ref>
*** [[Cryptochiroidea]] (46)
*** [[Grapsoidea]] (493, 28†)
*** [[Ocypodoidea]] (304, 14†)
*** [[Pinnotheroidea]] (304, 13†)

Recent studies have found the following [[superfamily (taxonomy)|superfamilies]] and [[family (biology)|families]] to not be [[monophyletic]], but rather [[paraphyletic]] or [[polyphyletic]]:<ref name="Ling"/><ref name="Wolfe2019"/><ref name="Tsang2022" /><ref name="Mendoza2022" />

* The [[Thoracotremata]] superfamily [[Grapsoidea]] is polyphyletic
* The [[Thoracotremata]] superfamily [[Ocypodoidea]] is polyphyletic
* The [[Heterotremata]] superfamily [[Calappoidea]] is polyphyletic
* The [[Heterotremata]] superfamily [[Eriphioidea]] is polyphyletic
* The [[Heterotremata]] superfamily [[Goneplacoidea]] is polyphyletic
* The [[Heterotremata]] superfamily [[Potamoidea]] is paraphyletic with respect to [[Gecarcinucoidea]], which is resolved by placing [[Gecarcinucidae]] within [[Potamoidea]]
* The [[Majoidea]] families [[Epialtidae]], [[Mithracidae]] and [[Majidae]] are polyphyletic with respect to each other
* The [[Dromioidea]] family [[Dromiidae]] may be paraphyletic with respect to [[Dynomenidae]]
* The [[Homoloidea]] family [[Homolidae]] is paraphyletic with respect to [[Latreilliidae]]
* The [[Xanthoidea]] family [[Xanthidae]] is paraphyletic with respect to [[Panopeidae]]