Editing Hermit crab (section)

==Classification==
The hermit crabs of Paguroidea are more closely related to [[squat lobster]]s and [[porcelain crab]]s than they are to true [[crab]]s ([[Brachyura]]). Together with the squat lobsters and porcelain crabs, they all belong to the [[infraorder]] [[Anomura]], the [[sister taxon]] to Brachyura.

However, the relationship of [[king crab]]s to the rest of Paguroidea has been a highly contentious topic. Many studies based on their physical characteristics, genetic information, and combined data demonstrate the longstanding hypothesis that the king crabs in the family [[Lithodidae]] are derived hermit crabs descended from [[pagurid]]s and should be classified as a family within Paguroidea.<ref>{{cite journal |journal = [[Proceedings of the Zoological Society of London]] |author1=J. D. MacDonald |author2=R. B. Pike |author3=D. I. Williamson |year=1957 |volume=128 |issue= 2 |pages=209–257 |title= Larvae of the British Species of ''Diogenes, Pagurus, Anapagurus,''and ''Lithodes'' |doi=10.1111/j.1096-3642.1957.tb00265.x}}</ref><ref>{{cite journal |author1=C. W. Cunningham |author2=N. W. Blackstone |author3=L. W. Buss |year=1992 |title=Evolution of king crabs from hermit crab ancestors |journal=[[Nature (journal)|Nature]] |volume=355 |issue=6360 |pages=539–542 |doi=10.1038/355539a0 |pmid=1741031 |bibcode=1992Natur.355..539C|s2cid=4257029 }}</ref><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=2012-01-02 |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=dead }}</ref><ref name="Tsang2011">{{cite journal|last1= Tsang|first1=L. M.|last2= Chan|first2= T.-Y.|last3= Ahyong|first3=S. T.|last4= Chu|first4=K. H.|title= Hermit to king, or Hermit to All: Multiple Transitions to Crab-like Forms from Hermit Crab Ancestors|journal= [[Systematic Biology]]|volume= 60|issue= 5|year= 2011|pages= 616–629|doi= 10.1093/sysbio/syr063|pmid= 21835822|doi-access= }}</ref> The molecular data has disproven an alternate view based on morphological arguments that the Lithodidae (king crabs) nest with the [[Hapalogastridae]] in a separate superfamily, Lithodoidea.<ref>{{cite journal |author1=Patsy A. McLaughlin |author2=Rafael Lemaitre |year=1997 |title=Carcinization in the anomura – fact or fiction? I. Evidence from adult morphology |journal=[[Contributions to Zoology]] |volume=67 |issue=2 |pages=79–123 |doi=10.1163/18759866-06702001 |doi-access=free |s2cid=46992448 }} [http://decapoda.nhm.org/pdfs/11727/11727.pdf PDF]</ref><ref name="Grave">{{cite journal|journal=[[Raffles Bulletin of Zoology]] |year=2009 |volume=Suppl. 21 |pages=1–109 |title=A classification of living and fossil genera of decapod crustaceans |author1=Sammy De Grave |author2=N. Dean Pentcheff |author3=Shane T. Ahyong |url=http://rmbr.nus.edu.sg/rbz/biblio/s21/s21rbz1-109.pdf |display-authors=etal |url-status=dead |archive-url=https://web.archive.org/web/20110606064728/http://rmbr.nus.edu.sg/rbz/biblio/s21/s21rbz1-109.pdf |archive-date=2011-06-06 }}</ref> As such, in 2023, the family Lithodidae was placed back into Paguroidea after having been moved out of it in 2007.<ref name="Poore & Ahyong (2023)">{{Cite book |last1=Poore |first1=Gary C. B. |title=Marine Decapod Crustacea: A Guide to Families and Genera of the World |last2=Ahyong |first2=Shane T. |publisher=CRC Press |year=2023 |isbn=978-1-4863-1178-1}}</ref>

Nine families are formally recognized in the superfamily Paguroidea,<ref name="WoRMS"/> containing around 1200 species in total in 135 genera.<ref name="checklist">{{cite journal|author1=Patsy A. McLaughlin |author2=Tomoyuki Komai |author3=Rafael Lemaitre |author4=Dwi Listyo Rahayu |year=2010 |editor1=Martyn E. Y. Low |editor2=S. H. Tan |title=Annotated checklist of anomuran decapod crustaceans of the world (exclusive of the Kiwaoidea and families Chirostylidae and Galatheidae of the Galatheoidea) - Chapter: Part I – Lithodoidea, Lomisoidea and Paguroidea |journal=[[Zootaxa]] |volume=Suppl. 23 |pages=5–107 |url=http://rmbr.nus.edu.sg/rbz/biblio/s23/s23rbz005-107.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120122104557/http://rmbr.nus.edu.sg/rbz/biblio/s23/s23rbz005-107.pdf |archive-date=2012-01-22 }}</ref>
[[File:991127-Chabahar-IMG 6650-HermitCrab-2.jpg|thumb|A hermit crab from [[Chabahar]], [[Iran]]]]
* [[Calcinidae]] <small>Fraaije, Van Bakel & Jagt, 2017</small> – seven genera<ref>{{cite journal |author1=René H.B. Fraaije |author2=Barry W.M. Van Bakel |author3=John W.M. Jagt |url=https://www.bsgf.fr/articles/bsgf/abs/2017/02/bsgf160027/bsgf160027.html |title=A new paguroid from the type Maastrichtian (upper Cretaceous, the Netherlands) and erection of a new family |journal=[[Bulletin de la Société Géologique de France]] |year=2017 |volume=188 |issue=3 |pages=1–4 |doi=10.1051/bsgf/2017185 |url-access=subscription }}</ref>
* [[Coenobitidae]] <small>Dana, 1851</small> – two genera: [[Coenobita|terrestrial hermit crabs]] and the [[coconut crab]]
* [[Diogenidae]] <small>Ortmann, 1892</small> – 20 genera of "left-handed hermit crabs"
* [[Lithodidae]] <small>Samouelle, 1819</small> – 15 genera of "king crabs"
* [[Paguridae]] <small>Latreille, 1802</small> – 76 genera of "true hermit crabs"
* [[Parapaguridae]] <small>Smith, 1882</small> – 10 genera of "anemone hermit crabs"
* [[Parapylochelidae]] <small>Fraaije ''et al.'', 2012</small> – two genera<ref>{{cite journal |author1=René H. B. Fraaije |author2=Adiël A. Klompmaker |author3=Pedro Artal |year=2012 |title=New species, genera and a family of hermit crabs (Crustacea, Anomura, Paguroidea) from a mid-Cretaceous reef of Navarra, northern Spain |journal=[[Neues Jahrbuch für Geologie und Paläontologie]] |volume=263 |issue=1 |pages=85–92 |doi=10.1127/0077-7749/2012/0213}}</ref>
* [[Pylochelidae]] <small>Bate, 1888</small> – 9 genera of "symmetrical hermit crabs"
* [[Pylojacquesidae]] <small>McLaughlin & Lemaitre, 2001</small> – two genera

===Phylogeny===
The placement of Paguroidea within [[Anomura]] can be shown in the [[cladogram]] below, which also shows the king crabs of [[Lithodidae]] as [[sister taxon]] to the hermit crabs of [[Paguridae]]:<ref name=Wolfe2019>{{cite journal |last1=Wolfe |first1=Joanna M. |last2=Breinholt |first2=Jesse W. |last3=Crandall |first3=Keith A. |last4=Lemmon |first4=Alan R. |last5=Lemmon |first5=Emily Moriarty |last6=Timm |first6=Laura E. |last7=Siddall |first7=Mark E. |last8=Bracken-Grissom |first8=Heather D. |display-authors=6 |date=24 April 2019 |title=A phylogenomic framework, evolutionary timeline and genomic resources for comparative studies of decapod crustaceans |journal=Proceedings of the Royal Society B |volume=286 |issue=1901 |doi=10.1098/rspb.2019.0079 |doi-access=free |pmid=31014217 |pmc=6501934}}</ref>
{{Anomura cladogram}}

===Fossil record===
The [[fossil record]] of ''[[In situ#Biology and biomedical engineering|in situ]]'' hermit crabs using [[gastropod shell]]s stretches back to the [[Late Cretaceous]]. Before that time, at least some hermit crabs used [[ammonite]] shells instead, as shown by a specimen of ''[[Palaeopagurus|Palaeopagurus vandenengeli]]'' from the [[Speeton Clay Formation]], [[Yorkshire]], [[United Kingdom|UK]], from the [[Lower Cretaceous]],<ref>{{cite journal |author=René H. Fraaije |date=January 2003 |title=The oldest ''in situ'' hermit crab from the Lower Cretaceous of Speeton, UK |journal=[[Palaeontology (journal)|Palaeontology]] |volume=46 |pages=53–57 |doi=10.1111/1475-4983.00286 |issue=1|bibcode=2003Palgy..46...53F |s2cid=128545998 |doi-access=free }}</ref> as well as a specimen of a [[Diogenidae|diogenid]] hermit crab from the [[Upper Jurassic]] of Russia.<ref>{{Cite journal|last=Mironenko|first=Aleksandr|date=January 2020|title=A hermit crab preserved inside an ammonite shell from the Upper Jurassic of central Russia: Implications to ammonoid palaeoecology|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=537|pages=109397|doi=10.1016/j.palaeo.2019.109397|bibcode=2020PPP...53709397M|doi-access=|s2cid=210298770 }}</ref> The earliest record of the superfamily extends back to the earliest part of the Jurassic, with the oldest known species being ''[[Schobertella|Schobertella hoelderi]]'' from the late [[Hettangian]] of Germany.<ref>{{Cite journal|last1=Fraaije|first1=René|last2=Schweigert|first2=Günter|last3=Nützel|first3=Alexander|last4=Havlik|first4=Philipe|date=2013-01-01|title=New Early Jurassic hermit crabs from Germany and France|journal=Journal of Crustacean Biology|language=en|volume=33|issue=6|pages=802–817|doi=10.1163/1937240X-00002191|issn=0278-0372|doi-access=free}}</ref>

===Aquatic and terrestrial hermit crabs===
Hermit crabs can be informally divided into two groups: aquatic hermit crabs and [[Terrestrial animal|terrestrial]] hermit crabs.<ref name=":132">{{cite web |last1=W. Michael |first1=Scott |title=Aquarium Hermit Crabs |url=http://www.fishchannel.com/saltwater-aquariums/species-info/invertebrates/hermit-danger.aspx |website=Fishchannel.com}}</ref>

The land hermit crabs belong to the [[family (biology)|family]] [[Coenobitidae]]. They spend most of their life on land in [[tropical]] areas, though they require access to water to keep their gills damp or wet to survive and to reproduce.