{{Short description|Extinct class of arthropods}} {{Use dmy dates|date=May 2024}} {{Automatic taxobox | fossil_range = Middle Cambrian-Late Ordovician {{Fossilrange|Cambrian Stage 3|Katian|latest=Early Devonian}}<ref name="Parry2024"></ref> <small>Possible --Silurian and Devonian records</small> | image = 20191028 Megacheirans Leanchoilia Haikoucaris Yohoia Fortiforceps.png | image_upright = 1.3 | image_caption = ''Alalcomenaeus'' (top left), ''Fortiforceps'' (top right), ''Haikoucaris'' (middle), ''Leanchoilia'' (bottom left) and ''Yohoia'' (bottom right). | taxon = Megacheira | authority = Hou and Bergström, 1997 | subdivision_ranks = Groups | subdivision = See text }} '''Megacheira''' (from Ancient Greek μέγας (''mégas''), meaning "great", and χείρ (''kheír''), meaning "hand", also historically '''great appendage arthropods''') is an extinct class of early Paleozoic predatory arthropods defined by their possession of spined "great appendages".<ref>{{Cite journal| doi = 10.1111/j.1096-3642.2009.00562.x| title = A new arthropod from the Early Cambrian of North Greenland, with a 'great appendage'-like antennula| date = March 2010| orig-date = 26 February 2010 <!-- first online publication -->| last1 = Stein | first1 = Martin| journal = Zoological Journal of the Linnean Society| volume = 158| issue = 3| pages = 477–500}}</ref> Their taxonomic position is controversial, with studies generally either considering them stem-group euarthropods, or stem-group chelicerates.<ref name=":5">{{Cite journal |last=Aria |first=Cédric |date=26 April 2022 |title=The origin and early evolution of arthropods |url=http://paleorxiv.org/4zmey/download |journal=Biological Reviews |volume=97 |issue=5 |language=en |pages=1786–1809 |doi=10.1111/brv.12864 |pmid=35475316 |s2cid=243269510 |issn=1464-7931 |access-date=8 May 2024 |archive-date=8 May 2024 |archive-url=https://web.archive.org/web/20240508131708/http://paleorxiv.org/4zmey/download |url-status=live }}</ref><ref>{{cite journal |last1=Liu |first1=Cong |last2=Fu |first2=Dongjing |last3=Wu |first3=Yu |last4=Zhang |first4=Xingliang |title=Cambrian euarthropod Urokodia aequalis sheds light on the origin of Artiopoda body plan |journal=iScience |date=July 2024 |volume=27 |issue=8 |article-number=110443 |doi=10.1016/j.isci.2024.110443|doi-access=free |pmid=39148713 |pmc=11325232 |bibcode=2024iSci...27k0443L }}</ref> The homology of the great appendages to the cephalic appendages of other arthropods is also controversial. Uncontested members of the group were present in marine environments worldwide from the lower Cambrian to the upper Ordovician.
== Morphology == {{multiple image | align = center | perrow = | image1 = 20190911 Megacheira Great Appendages.png | caption1 = Comparison of megacheiran great appendages | image2 = 20210701 Yohoia tenuis great appendage mobility.gif | caption2 = Movement range of the great appendage of ''Yohoia'' | total_width = 525 | direction = horizontal }} [[File:Tanglangia longicaudata reconstruction.png|thumb|3D model of ''Tanglangia longicaudata.'' en=endopod, ex=exopod]]
Megacheirans are defined by their possession of uniramous (unbranched) "great appendages", which are their first pair of head appendages. The first one or two proximalmost segments/podomeres closest towards the body are spineless (it has been argued that the supposed first of the two proximal podomeres is actually an arthrodial membrane<ref name=":4" />), while the remaining 3–4 more distal podomeres towards the ends of the limbs each typically bear a single upward pointing spine attached towards the distal (towards the tip) end of the segment, with the spineless proximal segment/s typically being connected to the spined distal segments by an elbow-like joint, which curled upwards.<ref name=":12">{{Cite journal |last1=Haug |first1=Joachim T. |last2=Waloszek |first2=Dieter |last3=Maas |first3=Andreas |last4=Liu |first4=Yu |last5=Haug |first5=Carolin |date=March 2012 |title=Functional morphology, ontogeny and evolution of mantis shrimp-like predators in the Cambrian: MANTIS SHRIMP-LIKE CAMBRIAN PREDATORS |journal=Palaeontology |language=en |volume=55 |issue=2 |pages=369–399 |doi=10.1111/j.1475-4983.2011.01124.x|doi-access=free }}</ref><ref name=":4" /> The great appendages have been interpreted as raptorial limbs involved in predation, with those of some genera such as ''Yohoia'' being structurally comparable to the raptorial maxillipeds of mantis shrimp.<ref name=":12" /> The spines on the great appendages of leanchoilid megacheirans such as ''Leanchoilia'' and ''Yawunik'' are elongated and whip-like, suggesting an antennae-like sensory role alongside predatory function.<ref name="Aria et al., 2015">{{cite journal |last1=Aria |first1=Cédric |last2=Caron |first2=Jean-Bernard |last3=Gaines |first3=Robert |date=2015 |title=A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny |journal=Palaeontology |volume=58 |issue=4 |pages=629–660 |doi=10.1111/pala.12161|s2cid=86443516 |doi-access=free |bibcode=2015Palgy..58..629A }}</ref> The body is divided into the head and the trunk, with the upper surface of the body being covered in overlapping tergites (upper body plates). On the head behind the great appendages and on the trunk were attached pairs of biramous (divided into two branches) limbs running along the body. The biramous limbs of megacheirans are homonomous (i.e. having little differentiation from each other), with endopods (the lower, leg-like branches) typically divided into seven segments/podomeres, and paddle-shaped exopods (the upper limb branches), which are fringed with thin lamellae. The morphology of the terminal telson segment is variable.<ref name=":4">{{Cite journal |last1=Aria |first1=Cédric |last2=Zhao |first2=Fangchen |last3=Zeng |first3=Han |last4=Guo |first4=Jin |last5=Zhu |first5=Maoyan |date=December 2020 |title=Fossils from South China redefine the ancestral euarthropod body plan |journal=BMC Evolutionary Biology |language=en |volume=20 |issue=1 |page=4 |doi=10.1186/s12862-019-1560-7 |issn=1471-2148 |pmc=6950928 |pmid=31914921 |doi-access=free |bibcode=2020BMCEE..20....4A }}</ref> The biramous limbs of at least some megacheirans have been suggested bear exites.<ref>{{Cite journal |last1=Liu |first1=Yu |last2=Edgecombe |first2=Gregory D. |last3=Schmidt |first3=Michel |last4=Bond |first4=Andrew D. |last5=Melzer |first5=Roland R. |last6=Zhai |first6=Dayou |last7=Mai |first7=Huijuan |last8=Zhang |first8=Maoyin |last9=Hou |first9=Xianguang |date=30 July 2021 |title=Exites in Cambrian arthropods and homology of arthropod limb branches |journal=Nature Communications |volume=12 |issue=1 |page=4619 |doi=10.1038/s41467-021-24918-8 |pmid=34330912 |pmc=8324779 |issn=2041-1723|doi-access=free |bibcode=2021NatCo..12.4619L }}</ref> == Taxonomy == Several subdivisions within the group are recognised including Jianfengiidae (including ''Fortiforceps'', ''Jianfengia'', ''Sklerolibyon'' and possibly ''Parapeytoia'') which are known from the Early Cambrian of China, as well as the Cheiromorpha (containing at least ''Yohoia'', ''Haikoucaris'', and Leanchoiliidae), known with certainty from the Early-Mid Cambrian of North America, China and Australia, which is distinguished from Jianfengiidae by having a fewer number of body segments (20+ in Jianfengiidae, as compared to typically only 11 to 13 in Cheiromorpha). The monophyly of Megacheira is uncertain, with some studies recovering the group as paraphyletic.<ref name=":4" /> The latest unambiguous megacheiran is the leanchoiliid ''Lomankus'' from the Upper Ordovician of North America.<ref name="Parry2024">{{Cite journal |last=Parry |first=Luke A. |last2=Briggs |first2=Derek E.G. |last3=Ran |first3=Ruixin |last4=O'Flynn |first4=Robert J. |last5=Mai |first5=Huijuan |last6=Clark |first6=Elizabeth G. |last7=Liu |first7=Yu |date=October 2024 |title=A pyritized Ordovician leanchoiliid arthropod |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982224013678 |journal=Current Biology |language=en |doi=10.1016/j.cub.2024.10.013|doi-access=free }}</ref>
''Parapeytoia'' from the Cambrian of China which was formerly misinterpreted as a radiodont was later suggested to be a member of this group.<ref>{{Cite journal |last=Stein |first=Martin |date=1 March 2010 |title=A new arthropod from the Early Cambrian of North Greenland, with a 'great appendage'-like antennula |url=https://academic.oup.com/zoolinnean/article/158/3/477/3798454 |journal=Zoological Journal of the Linnean Society |language=en |volume=158 |issue=3 |pages=477–500 |doi=10.1111/j.1096-3642.2009.00562.x |issn=0024-4082 |url-access=subscription |access-date=29 October 2019 |archive-date=3 November 2019 |archive-url=https://web.archive.org/web/20191103021239/https://academic.oup.com/zoolinnean/article/158/3/477/3798454 |url-status=live }}</ref><ref>{{Cite book |last1=Xian-Guang |first1=Hou |url=https://books.google.com/books?id=2YWhDgAAQBAJ&q=Tanglangia&pg=PA184 |title=The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life |last2=Siveter |first2=David J. |last3=Siveter |first3=Derek J. |last4=Aldridge |first4=Richard J. |last5=Pei-Yun |first5=Cong |last6=Gabbott |first6=Sarah E. |last7=Xiao-Ya |first7=Ma |last8=Purnell |first8=Mark A. |last9=Williams |first9=Mark |date=24 April 2017 |publisher=John Wiley & Sons |isbn=978-1-118-89638-9 |language=en |access-date=10 May 2021 |archive-date=8 May 2024 |archive-url=https://web.archive.org/web/20240508131607/https://books.google.com/books?id=2YWhDgAAQBAJ&q=Tanglangia&pg=PA184#v=snippet&q=Tanglangia&f=false |url-status=live }}</ref><ref>{{Cite journal |last1=Daley |first1=Allison C. |last2=Budd |first2=Graham E. |last3=Caron |first3=Jean-Bernard |last4=Edgecombe |first4=Gregory D. |last5=Collins |first5=Desmond |date=20 March 2009 |title=The Burgess Shale Anomalocaridid Hurdia and Its Significance for Early Euarthropod Evolution |journal=Science |language=en |volume=323 |issue=5921 |pages=1597–1600 |doi=10.1126/science.1169514 |issn=0036-8075 |pmid=19299617 |bibcode=2009Sci...323.1597D |s2cid=206517995}}</ref> Possible megacheirans include ''Enalikter'' described from the Silurian of the United Kingdom, and ''Bundenbachiellus'' from the Early Devonian of Germany;<ref>{{Cite journal |last1=Siveter |first1=Derek J. |last2=Briggs |first2=Derek E. G. |last3=Siveter |first3=David J. |last4=Sutton |first4=Mark D. |last5=Legg |first5=David |last6=Joomun |first6=Sarah |date=7 March 2014 |title=A Silurian short-great-appendage arthropod |journal=Proceedings of the Royal Society B |volume=281 |issue=1778 |article-number=20132986 |doi=10.1098/rspb.2013.2986 |pmc=3906945 |pmid=24452026}}</ref><ref>{{Cite journal |author1=Derek J. Siveter |author2=Derek E. G. Briggs |author3=David J. Siveter |author4=Mark D. Sutton |author5=David Legg |author6=Sarah Joomun |year=2015 |title=''Enalikter aphson'' is an arthropod: a reply to Struck ''et al.'' (2014) |journal=Proceedings of the Royal Society B |volume=282 |issue=1804 |article-number=20142663 |doi=10.1098/rspb.2014.2663 |pmc=4375861}}</ref> due to their possession of great appendage-like cephalic appendages. However, their relationship to megacheirans has been questioned, due to the uncertain homology of their appendages.<ref>{{Cite journal |last=Aria |first=Cédric |date=October 2022 |title=The origin and early evolution of arthropods |url=http://paleorxiv.org/4zmey/download |journal=Biological Reviews |language=en |volume=97 |issue=5 |pages=1786–1809 |doi=10.1111/brv.12864 |pmid=35475316 |s2cid=243269510 |issn=1464-7931 |access-date=8 May 2024 |archive-date=8 May 2024 |archive-url=https://web.archive.org/web/20240508131708/http://paleorxiv.org/4zmey/download |url-status=live }}</ref> ''Kootenichela'' has been suggested to be a chimera of various arthropod taxa.<ref name=":4" /> Previous inclusion of some "bivalved" genera such as ''Forfexicaris'', ''Ovalicephalus'', and ''Occacaris'' to Megacheira was questioned by later investigations.<ref name=":0">{{Cite journal |last1=Ortega-Hernández |first1=Javier |last2=Janssen |first2=Ralf |last3=Budd |first3=Graham E. |date=1 May 2017 |title=Origin and evolution of the panarthropod head – A palaeobiological and developmental perspective |journal=Arthropod Structure & Development |volume=46 |issue=3, ''Evolution of Segmentation'' |pages=354–379 |doi=10.1016/j.asd.2016.10.011 |issn=1467-8039 |pmid=27989966|doi-access=free |bibcode=2017ArtSD..46..354O }}</ref> The Late Cambrian Orsten taxon ''Oelandocaris'' typically considered to be a crustacean relative, has also been suggested in some studies to be a megacheiran.<ref>{{Cite journal |last1=Aria |first1=Cédric |last2=Caron |first2=Jean-Bernard |date=May 2017 |title=Burgess Shale fossils illustrate the origin of the mandibulate body plan |url=http://www.nature.com/articles/nature22080 |journal=Nature |language=en |volume=545 |issue=7652 |pages=89–92 |doi=10.1038/nature22080 |pmid=28445464 |bibcode=2017Natur.545...89A |s2cid=4454526 |issn=0028-0836 |url-access=subscription |access-date=12 January 2023 |archive-date=23 September 2022 |archive-url=https://web.archive.org/web/20220923174326/https://www.nature.com/articles/nature22080 |url-status=live }}</ref>
{{gallery|Artistic reconstructions of Fortiforceps foliosa and Sklerolibyon maomima gen. et sp. nov. in early Cambrian Gondwanian seas.png|Life reconstruction of ''Fortiforceps'' (left) and ''Sklerolibyon'' (right)|Jianfengia reconstruction.png|Life restoration of ''Jianfengia''|2012 Leanchoilia superlata 06.png|Closeup of great appendages of ''Leanchoilia superlata''|Y._kootenayi.png|Life restoration of ''Yawunik''|File:Parry et al. 2024 f03 (reconstruction).png|Life restoration of ''Lomankus''|File:Oestokerkus megacholix reconstruction.png|Life restoration of ''Oestokerkus''|||width=200|height=180|align=center}}
=== List of genera ===
* †''Tanglangia'' * †''Oelandocaris''? * †Jianfengiidae ** ''Sklerolibyon'' ** ''Jianfengia'' ** ''Parapeytoia''? ** ''Fortiforceps'' * †Kootenichelidae? ** ''Kootenichela''? ** ''Worthenella''? ** ''Pseudoiulia''? * †Cheiromorpha ** ''Yohoia'' ** ''Haikoucaris'' ** Leanchoiliida *** Enaliktidae? **** ''Enalikter''? **** ''Bundenbachiellus''? *** Leanchoiliidae **** ''Actaeus'' **** ''Alalcomenaeus'' **** ''Leanchoilia'' **** ''Oestokerkus'' **** ''Yawunik'' **** ''Kanoshoia'' **** ''Lomankus''
=== Relationship to other arthropods === {{Main|Arthropod head problem}}
Megacheirans are either suggested to be stem-group chelicerates (the group containing arachnids, sea spiders and horseshoe crabs, among other extinct groups) or stem-group arthropods outside the split between Chelicerata and the other major group of living arthropods, Mandibulata (which includes crustaceans, insects, centipedes and millipedes, among others).<ref name=":5" /> The former hypothesis is based on the chelicerae-like morphology of the great appendages,<ref>{{Cite journal |last1=Chen |first1=Junyuan |last2=Waloszek |first2=Dieter |last3=Maas |first3=Andreas |date=2004 |title=A new 'great-appendage' arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages |journal=Lethaia |language=en |volume=37 |issue=1 |pages=3–20 |bibcode=2004Letha..37....3C |doi=10.1080/00241160410004764 |issn=1502-3931}}</ref><ref name=":3">{{Cite journal |last=Chen |first=Jun-Yuan |date=2009 |title=The sudden appearance of diverse animal body plansduring the Cambrian explosion |journal=The International Journal of Developmental Biology |volume=53 |issue=5–6 |pages=733–751 |doi=10.1387/ijdb.072513cj |issn=1696-3547 |pmid=19557680 |doi-access=free}}</ref><ref name=":2">{{Cite journal |last1=Haug |first1=Joachim T. |last2=Waloszek |first2=Dieter |last3=Maas |first3=Andreas |last4=Liu |first4=Yu |last5=Haug |first5=Carolin |date=March 2012 |title=Functional morphology, ontogeny and evolution of mantis shrimp-like predators in the Cambrian: MANTIS SHRIMP-LIKE CAMBRIAN PREDATORS |journal=Palaeontology |language=en |volume=55 |issue=2 |pages=369–399 |doi=10.1111/j.1475-4983.2011.01124.x |s2cid=82841481 |doi-access=free}}</ref> alongside neuroanatomy<ref name=":1">{{Cite journal |last1=Tanaka |first1=Gengo |last2=Hou |first2=Xianguang |last3=Ma |first3=Xiaoya |last4=Edgecombe |first4=Gregory D. |last5=Strausfeld |first5=Nicholas J. |date=17 October 2013 |title=Chelicerate neural ground pattern in a Cambrian great appendage arthropod |journal=Nature |volume=502 |issue=7471 |pages=364–367 |bibcode=2013Natur.502..364T |doi=10.1038/nature12520 |pmid=24132294 |s2cid=4456458}}</ref> and the presence of a reduced labrum<ref>{{Cite journal |last1=Liu |first1=Yu |last2=Ortega-Hernández |first2=Javier |last3=Zhai |first3=Dayou |last4=Hou |first4=Xianguang |date=25 June 2020 |title=A Reduced Labrum in a Cambrian Great-Appendage Euarthropod |journal=Current Biology |language=en |volume=30 |issue=15 |pages=3057–3061.e2 |bibcode=2020CBio...30E3057L |doi=10.1016/j.cub.2020.05.085 |issn=0960-9822 |pmid=32589912 |s2cid=220057956 |doi-access=free}}</ref> resembling those of modern chelicerates. The proponents of this hypothesis argue that chelicerae and the great appendages are homologous structures.<ref>{{Cite journal |last1=Tanaka |first1=Gengo |last2=Hou |first2=Xianguang |last3=Ma |first3=Xiaoya |last4=Edgecombe |first4=Gregory D. |last5=Strausfeld |first5=Nicholas J. |date=17 October 2013 |title=Chelicerate neural ground pattern in a Cambrian great appendage arthropod |url=http://www.nature.com/articles/nature12520 |url-status=live |journal=Nature |language=en |volume=502 |issue=7471 |pages=364–367 |bibcode=2013Natur.502..364T |doi=10.1038/nature12520 |issn=0028-0836 |pmid=24132294 |s2cid=4456458 |url-access=subscription |archive-url=https://web.archive.org/web/20221016211810/https://www.nature.com/articles/nature12520 |archive-date=16 October 2022 |access-date=12 January 2023}}</ref> Other studies suggest that the megacheirans are stem-group arthropods based on the argument that the great appendages are homologous to the frontal appendages of stem-group arthropods like ''Isoxys'' and radiodonts. This identity is disputed, with other authors suggesting that the frontal appendages of radiodonts are homologous to the labrum of modern arthropods.<ref name=":4" /> Some studies have suggested based on brain and nervous system anatomy that while some megacheirans are stem-chelicerates, others are stem-mandibulates.<ref>{{Cite journal |last1=Strausfeld |first1=N. J. |last2=Andrew |first2=D. R. |last3=Hou |first3=X. |last4=Hirth |first4=F. |year=2025 |title=Brain anatomy of the Cambrian fossil ''Jianfengia multisegmentalis'' informs euarthropod phylogeny |journal=Nature Communications |volume=16 |doi=10.1038/s41467-025-62849-w |pmc=12394709 |pmid=40877252 |doi-access=free |article-number=7938}}</ref>
Cladogram of Arthropoda after Aria et al. 2020, showing megacheirans (as indicated by the orange bar) as a paraphyletic stem group to modern arthropods:<ref name=":4" />
{{clade |label1=Arthropoda (''s. l.'') |1={{clade |1=†''Opabinia'' 100px |2={{clade |1=†''Anomalocaris'' 100px |2={{clade |1=†Hurdiidae 100px |label2=Deuteropoda |2={{clade |1=†Isoxyidae 100px |2={{clade |bar1=orange |label1=†Jianfengiidae |1={{clade |1=†''Jianfengia'' 100px |2={{clade |1=†''Sklerolibyon'' 100px |2={{clade |1=†''Fortiforceps'' 100px |2=†''Parapeytoia'' 100px }}}}}} |2={{clade |bar1=orange |1=†''Yohoia'' 100px |2={{clade |bar1=orange |1={{clade |1=†''Haikoucaris'' 100px |2=†Leanchoiliidae 100px }} |2={{clade |label1=Chelicerata |1={{clade |1=Pycnogonida (sea spiders) 100px |2={{clade |1=†Habeliida 100px |2=Euchelicerata 100px 100px }}}} |label2=Antennulata |2={{clade |1={{clade |1=†''Kiisortoqia'' 100px |2=†Artiopoda (including Trilobita) 100px }} |2={{clade |1=†''Marrella'' 100px |2={{clade |1=†''Aquilonifer'' 100px |2=Mandibulata 100px 100px }}}}}}}}}}}}}}}}}}}}}}|style=font-size:85%}}
Placement of monophyletic Megacheira at the base of Chelicerata, after Parry et al. 2024:<ref name="Parry2024"></ref><sup>supplemental material</sup> {{clade |label1=Arthropoda (''s. l.'') |1={{clade |1=†''Opabinia'' 100px |2={{clade |1=†Radiodonta (e.g. ''Anomalocaris'') 100px |label2=Deuteropoda |2={{clade |1={{extinct}}''Fengzhengia'' 100px |2={{extinct}}''Kylinxia'' 100px |3={{clade |label1=Total group Mandibulata |1={{clade |1={{clade |1=†''Kiisortoqia'' 100px |2={{extinct}}''Bushizheia'' 100px }} |2={{clade |1=†Isoxyidae 100px |2={{clade |1=†Artiopoda (including Trilobita) 100px |2={{clade |1=†Fuxianhuiida 100px |2={{clade |1=†Hymenocarina 100px |2=Mandibulata (crown group) 100px 100px }}}}}}}}}} |label2=Pan-Chelicerata |2={{clade |1={{clade |1=†''Habelia'' 100px |2={{clade |1=†''Mollisonia'' 100px |2={{clade |1=Xiphosura (horseshoe crabs) 100px |2={{clade |1=†''Dibasterium'' 100px |2=†''Offacolus'' 100px }}}}}}}} |label2=Megacheira |2={{clade |1={{clade |1=†''Haikoucaris'' 100px |label2=Leanchoiliidae |2={{clade |1=†''Oestokerkus'' 100px |2={{clade |1=†''Yawunik'' 100px |2=†''Alalcomenaeus'' 100px }} |3={{clade |1=†''Lomankus'' 100px |2=†''Leanchoilia'' 100px }}}}}} |2={{clade |1={{clade |1=†''Tanglangia'' 100px |2=†''Yohoia'' 100px }} |label2=Jianfengiidae |2={{clade |1= †''Fortiforceps'' 100px |2={{clade |1=†''Sklerolibyon'' 100px |2=†''Jianfengia'' 100px }}}}}}}}}}}}}}}}}}|style=font-size:85%}}Placement of megacheirans (represented by orange bar) as a paraphyletic assemblage at the base of total-group Chelicerata, after Lerosey-Aubril and Ortega-Hernández (2026):<ref name=":02">{{Cite journal |last=Lerosey-Aubril|first=Rudy|last2=Ortega-Hernández|first2=Javier|date=2026-04-01|title=A chelicera-bearing arthropod reveals the Cambrian origin of chelicerates|url=https://www.nature.com/articles/s41586-026-10284-2|journal=Nature|language=en|pages=1–7|doi=10.1038/s41586-026-10284-2|issn=1476-4687|doi-access=free}}</ref>{{clade|{{clade |label1=Pan-Chelicerata |1={{clade | bar1=orange |1={{clade |1=†''Jianfengia'' 100px |2=†''Sklerolibyon'' 100px }} |2={{clade |1=†''Fortiforceps'' 100px | bar1=orange |2=†''Yohoia'' 100px | bar2=orange |3={{clade | bar1=orange |1=†''Haikoucaris'' 100px |2=†Leanchoiliidae 100px | bar2=orange }} |4={{clade |1=†Mollisoniida 100px |2={{clade |1=†''Wisangocaris'' 100px |2=†''Habelia'' 100px |3={{clade |1=†''Sanctacaris'' 100px |2=†''Utahcaris'' }} |label4=chelicerae present |4={{clade |1=†''Megachelicerax'' 100px |2={{clade |1=†''Offacolus'' 100px |2={{clade |1={{clade |1=†''Setapedites'' 100px |2=†''Dibasterium'' 100px }} |2={{clade |1=†''Weinbergina'' 100px |2={{clade |1=†''Venustulus'' 100px |2={{clade |1=Pycnogonida (sea spiders) 100px |2={{clade |1=Xiphosura (horseshoe crabs) 100px |2={{clade |1=Arachnida 100px |2=†Eurypterida (sea scorpions) 70px }}}}}}}}}}}}}}}}}}}}}}}}}}|style=font-size:85%}}
==References== {{Reflist|30em}}
{{Megacheira}} {{Taxonbar|from=Q1946246}} {{Authority control}}
Category:Megacheira Category:Arthropod classes Category:Prehistoric protostome classes