Artiopoda

{{Short description|Group of extinct arthropods}} {{Automatic taxobox | fossil_range = {{fossil_range|Cambrian|Permian|Early Cambrian - Late Permian}} | image = Misszhouia.png | image_caption = ''Misszhouia'', a nektaspid | image2 = 20200415_Cheloniellon_calmani.png | image2_caption = ''Cheloniellon'', a cheloniellid | taxon = Artiopoda | authority = Hou and Bergstrom, 1997 | subdivision_ranks = Subgroups | subdivision = *†''Siriocaris''? *†''Squamacula'' *†''Thulaspis'' *†''Urokodia'' <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 |pmid=39148713 |pmc=11325232 |bibcode=2024iSci...27k0443L |url=https://www.cell.com/iscience/pdf/S2589-0042(24)01668-7.pdf}}</ref> *†''Falcatamacaris'' *†''Molaria'' *†''Bailongia'' *†''Notchia''?<ref>{{cite journal |last1=Lerosey-Aubril |first1=Rudy |title=Notchia weugi gen. et sp. nov.: a new short-headed arthropod from the Weeks Formation Konservat-Lagerstätte (Cambrian; Utah) |journal=Geological Magazine |date=March 2015 |volume=152 |issue=2 |pages=351–357 |doi=10.1017/S0016756814000375 |bibcode=2015GeoM..152..351L }}</ref> *†'''Strabopida'''? *†'''Protosutura''' **†''Acanthomeridion'' **†''Zhiwenia'' **†''Australimicola'' *†'''Trilobitomorpha''' **†''Retifacies''? **†''Pygmaclypeatus''? **†''Campanamuta''? **†''Kwanyinaspis'' **†''Arthroaspis'' **†''Tonglaiia''<ref name="Zhu2023">{{cite journal |last1=Zhu |first1=Y. |last2=Zeng |first2=H. |last3=Liu |first3=Y. |last4=Zhao |first4=F. |title=New artiopodan euarthropods from the Chengjiang fauna (Cambrian, Stage 3) at Malong, Yunnan, China |journal=Acta Palaeontologica Polonica |date=2023 |volume=68 |doi=10.4202/app.01080.2023|doi-access=free }}</ref> **†'''Nektaspida''' **†'''Trilobita''' **†'''Agnostida'''?(Traditionally included within Trilobita) **†'''Conciliterga''' **†'''Xandarellida''' (=Petalopleura) *†'''Vicissicaudata''' **†''Sidneyia'' **†''Emeraldella'' **†''Etainia'' **†''Kodymirus'' **†''Eozetetes'' **†''Tardisia'' **†''Carimersa'' **†'''Cheloniellida''' **†'''Aglaspidida''' | subdivision_ref = }} '''Artiopoda''' is a clade of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997<ref>Hou, X. & Bergström, J. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, No. 45. Scandinavian University Press, Oslo, 22 Dec 1997: 116 pp.[http://foreninger.uio.no/ngf/FOS/pdfs/F&S_45.pdf]</ref> to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomorpha. Trilobites, in part due to abundance of findings owing to their mineralized exoskeletons, are by far the best recorded, diverse, and long lived members of the clade. Other members, which lack mineralised exoskeletons, are known mostly from Cambrian deposits.<ref>{{Cite journal |last1=Schmidt |first1=Michel |last2=Hou |first2=Xianguang |last3=Zhai |first3=Dayou |last4=Mai |first4=Huijuan |last5=Belojević |first5=Jelena |last6=Chen |first6=Xiaohan |last7=Melzer |first7=Roland R. |last8=Ortega-Hernández |first8=Javier |last9=Liu |first9=Yu |title=Before trilobite legs: ''Pygmaclypeatus daziensis'' reconsidered and the ancestral appendicular organization of Cambrian artiopods |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=2022 |volume=377 |issue=1847 |article-number=20210030 |doi=10.1098/rstb.2021.0030 |pmid=35125003 |biorxiv=10.1101/2021.08.18.456779 }}</ref>

==Description== [[File:Retifacies diagram.webp|left|thumb|Morphology of Cambrian artiopod ''Retifacies'', showing the morphology of the limbs (E, F) Key for limb morphology: exopod (exo) exite (exi) protopodite (pt) podomere (pd) spine/setae (s) terminal claw (tc)]] According to Stein and Selden (2012) artiopods are recognised by the possession of filiform (elongate and relatively thin) antennae, limbs with bilobate exopods (upper branches), with the proximal (closest to base of the limb) lobe being elongate and bearing a lamella, while the distal (further from the limb base) lobe is paddle-shaped and setiforous (bearing hair-or bristle like structures). The limb endopod (inner, leg-like branch) has seven podomeres/segments, with first four podomeres bearing inward facing (endite) structures, while podomeres five and six are stenopodous (cylindrical and stout). Common plesiomorphies (ancestral traits) also include the antennules and at least three sets of post-antennular limbs being attached to the head shield, the postantennular limbs having no or little differentiation into distinct morphologies, and broad paratergal folds which contribute to the dorsoventrally (along the up-down axis) flattened look of artiopods.<ref name=":0">{{Cite journal |last1=Stein |first1=Martin |last2=Selden |first2=Paul A. |date=June 2012 |title=A restudy of the Burgess Shale (Cambrian) arthropod Emeraldella brocki and reassessment of its affinities |journal=Journal of Systematic Palaeontology |language=en |volume=10 |issue=2 |pages=361–383 |doi=10.1080/14772019.2011.566634 |bibcode=2012JSPal..10..361S |issn=1477-2019 |s2cid=55018927}}</ref> The limbs of artiopods have also been suggested to bear exites, which were described as similar those of the megacheiran ''Leanchoilia'' and probably not homologous to those present in crustaceans.<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=2021-07-30 |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>

{{gallery|The American journal of science (1896) (17966037580) (cropped).jpg|Restoration of the trilobite ''Triarthrus eatoni''|Naraoia magna reconstruction.png|Restoration of ''Naraoia magna'' (Nektaspida)|File:Sidneyia minor.png|Life restoration of ''Sidneyia'' (Vicissicaudata)|Sinoburius_7.png|Diagram of ''Sinoburius'' (Xandarellida)|Olenoides_serratus_male_diagrammatic_reconstruction.svg|Diagram of ''Olenoides serratus'' (Trilobita)|width=200|height=250|20240212_Aglaspis_spinifer.png|Life restoration of ''Aglaspis'' (Aglaspidida)|File:20240121 Tegopelte gigas diagrammatic reconstruction.png|Life restoration of ''Tegopelte'' (Conciliterga)|File:Pleuroctenium granulatum.JPG|Life restoration of ''Pleuroctenium'' (Agnostida)}}

== Taxonomy == === Internal taxonomy === The Artiopoda have been considered by many studies to consist of two major clades; one reusing Trilobitomorpha to encompass trilobites, nektaspids, concilitergans and xandarellids, and the other called Vicissicaudata encompassing aglaspidids, xenopods and cheloniellids.<ref>{{Cite journal|last1=Ortega-Hernández|first1=Javier|last2=Legg|first2=David A.|last3=Braddy|first3=Simon J.|date=February 2013|title=The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda|journal=Cladistics|language=en|volume=29|issue=1|pages=15–45|doi=10.1111/j.1096-0031.2012.00413.x|pmid=34814371 |bibcode=2013Cladi..29...15O |s2cid=85744103 }}</ref> A small group, Protosutura, comprising ''Zhiwenia'', ''Acanthomeridion'' and ''Australimicola,'' has been recognised based on the shared presence of simple sutures on the top (dorsal surface) of the carapace where it splits during ecdysis (moulting), and a short tailspine. This group is often placed basal to the Trilobitomorpha-Vicissicaudata split,<ref name="BETA">{{cite journal |last1=Du |first1=Kun-sheng |last2=Ortega-Hernández |first2=Javier |last3=Yang |first3=Jie |last4=Zhang |first4=Xi-guang |date=June 2019 |title=A soft-bodied euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports a new clade of basal artiopodans with dorsal ecdysial sutures |journal=Cladistics |volume=35 |issue=3 |pages=269–281 |doi=10.1111/cla.12344 |pmid=34622993}}</ref> alongside other taxa like ''Squamacula''. These relationships are not always recovered.<ref name="Berks2023">{{cite journal |last1=Berks |first1=H. O. |last2=Lunde Nielsen |first2=M. |last3=Flannery-Sutherland |first3=J. |last4=Thorshøj Nielsen |first4=A. |last5=Park |first5=T.-Y. S. |last6=Vinther |first6=J. |date=2023 |title=A possibly deep branching artiopodan arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland) |journal=Papers in Palaeontology |volume=9 |issue=3 |article-number=e1495 |doi=10.1002/spp2.1495|doi-access=free |bibcode=2023PPal....9E1495B }}</ref>

=== Relationships with other arthropods === The relationship of Artiopoda with the two major clades of modern arthropods, Chelicerata (the group of sea spiders, horseshoe crabs and arachnids such as spiders and scorpions) and Mandibulata (which contains insects, crustaceans, centipedes and millipedes, among others), are unresolved, with some phylogenies recovering Artiopoda as more closely to chelicerates, forming the clade Arachnomorpha, while others recover Artiopoda as more closely related to mandibulates, forming the clade Antennulata.<ref>{{Cite journal |last=Aria |first=Cédric |date=2022-04-26 |title=The origin and early evolution of arthropods |url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12864 |journal=Biological Reviews |volume=97 |issue=5 |language=en |pages=1786–1809 |doi=10.1111/brv.12864 |pmid=35475316 |bibcode=2022BioRv..97.1786A |s2cid=243269510 |issn=1464-7931|url-access=subscription }}</ref> Some studies place them as stem-group euarthropods, with mandibulates and chelicerates more closely related to each other than either is to Artiopoda.<ref name="Berks2023" /> Some studies have recovered a close relationship with Marrellomorpha, with the proposed clade including Artiopoda and Marrellomorpha dubbed Lamellipedia, though this relationship is not found in other analyses.<ref>{{Cite journal |last1=Moysiuk |first1=Joseph |last2=Izquierdo-López |first2=Alejandro |last3=Kampouris |first3=George E. |last4=Caron |first4=Jean-Bernard |date=July 2022 |title=A new marrellomorph arthropod from southern Ontario: a rare case of soft-tissue preservation on a Late Ordovician open marine shelf |journal=Journal of Paleontology |language=en |volume=96 |issue=4 |pages=859–874 |doi=10.1017/jpa.2022.11 |issn=0022-3360|doi-access=free |bibcode=2022JPal...96..859M }}</ref><ref>{{Cite journal |last=Stein |first=Martin |date=November 2013 |title=Cephalic and appendage morphology of the Cambrian arthropod Sidneyia inexpectans |url=https://linkinghub.elsevier.com/retrieve/pii/S0044523113000375 |journal=Zoologischer Anzeiger - A Journal of Comparative Zoology |language=en |volume=253 |issue=2 |pages=164–178 |doi=10.1016/j.jcz.2013.05.001|url-access=subscription }}</ref> The enigmatic artiopodan-like arthropod ''Kiisortoqia,'' which bears large "frontal appendages" has been suggested to be closely related to Artiopoda in some analyses.<ref name="Berks2023" />

=== Phylogeny ===

==== Internal phylogeny ==== After Jiao et al. 2021.<ref>{{Cite journal |last1=Jiao |first1=De-Guang |last2=Du |first2=Kun-Sheng |last3=Zhang |first3=Xi-Guang |last4=Yang |first4=Jie |last5=Eggink |first5=Daniel |date=May 2022 |title=A new small soft-bodied non-trilobite artiopod from the Cambrian Stage 4 Guanshan Biota |journal=Geological Magazine |language=en |volume=159 |issue=5 |pages=730–734 |doi=10.1017/S0016756821001254 |issn=0016-7568|doi-access=free |bibcode=2022GeoM..159..730J }}</ref> {{clade| style=font-size:85%; line-height:85% |label1=Artiopoda |1={{clade |1=''Squamacula clypeata'' |2={{clade |label1=Protosutura |1={{clade |1={{clade |1=''Zhiwenia coronata'' |2=''Australimicola spriggi'' }} |2={{clade |1=''Acanthomeridion serratum'' |2=''Acanthomeridion anacanthus'' }} }} |2={{clade |label2=Trilobitomorpha |label3=Vicissicaudata |1=''Bailongia longicaudata'' |2={{clade |1=''Retifacies abnormalis'' |2={{clade |1={{clade |1={{clade |1=''Kwanyinaspis maotiashanensis'' |label2=Trilobita |2={{clade |1=''Olenoides serratus'' |2=''Eoredlichia intermedia'' }} }} |label2=Conciliterga |2={{clade |1=''Haifengella corona'' |2={{clade |1={{clade |1=''Kuamaia lata'' |2=''Helmetia expansa'' }} |2={{clade |1=''Tegopelte gigas'' |2=''Skioldia aldna'' |3=''Saperion glumaceum'' }} }} }} }} |2={{clade |label1=Xandarellida |label2=Nektaspida |1={{clade |1=''Cindarella eucalla'' |2={{clade |1=''Luohuilinella deletres'' |2=''Luohuilinella rarus'' |3={{clade |1=''Sinoburius lunaris'' |2={{clade |1=''Xandarella spectaculum'' |2=''Phytophilaspis pergamena'' }} }} }} }} |2={{clade |1=''Buenaspis forteyi'' |2={{clade |1=''Tariccoia arrusensis'' |2=''Soomaspis splendida'' |3=''Liwia convexa'' }} |3={{clade |1=''Naraoia spinosa'' |2={{clade |1=''Naraoia compacta'' |2=''Misszhouia longicaudata'' }} }} }} }} }} }} |3={{clade |1=''Sidneyia inexpectans'' |2={{clade |1=''Emeraldella brocki'' |label2=Cheloniellida |2={{clade |1=''Cheloniellon calmani'' |2={{clade |1=''Triopus draboviensis'' |2=''Duslia insignis'' }} }} |3={{clade |1=''Kodymirus vagans'' |2={{clade |1=''Eozetetes gemmelli'' |label2=Aglaspidida |2={{clade |1=''Beckwithia typa'' |2={{clade |1={{clade |1=''Chlupacaris dubia'' |2={{clade |1=''Quasimodaspis brentsae'' |2={{clade |1=''Tremaglaspis unite'' |2={{clade |1=''Tremaglaspis vanroyi'' |2=''Brachyaglaspis singularis'' }} }} }} |3={{clade |1=''Cyclopites vulgaris'' |2=''Australaglaspis stonyensis'' |3={{clade |1=''Uarthrus instabilis'' |2=''Flobertia kochi'' |3={{clade |1=''Aglaspella granulifera'' |2={{clade |1=''Gogglops ensifer'' |2={{clade |1=''Glypharthrus simplex'' |2=''Aglaspis spinifer'' }} }} |3={{clade |1=''Chraspedops modesta'' |2={{clade |1=''Glypharthrus thomasi'' |2={{clade |1=''Glypharthrus trispinicaudatus'' |2=''Glypharthrus magnoculus'' }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }}Implied weights parsimony phylogeny after Berks et al. 2023.<ref name=":02">{{Cite journal |last1=Berks |first1=H. O. |last2=Nielsen |first2=M. L. |last3=Flannery-Sutherland |first3=J. |last4=Nielsen |first4=A. T. |last5=Park |first5=T.-Y. S. |last6=Vinther |first6=J. |year=2023 |title=A possibly deep branching artiopodan arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland) |journal=Papers in Palaeontology |volume=9 |issue=3 |at=e1495 |doi=10.1002/spp2.1495 |s2cid=259253098 |doi-access=free |bibcode=2023PPal....9E1495B }}</ref>{{clade|{{clade |1={{clade |1=''Thulaspis'' 100px |2=''Squamacula'' 80px }} |2={{clade |label1=Protosutura |1={{clade |1=''Zhiwenia'' 50px |2=''Australimicola'' 35px |3=''Acanthomeridion'' 100px }} |2={{clade |label1=Vicissicaudata |1={{clade |1=''Sidneyia'' 100px |2={{clade |1=Cheloniellida 70px |2={{clade |1=''Emeraldella'' 70px |2={{clade |1=''Kodymirus'' 70px |2={{clade |1=''Eozetetes'' |2=Aglaspidida 100px }}}}}}}}}} |label2=Trilobitomorpha |2={{clade |1={{clade |1=''Retifacies'' 100px |2=''Pygmaclypeatus'' 100px }} |2={{clade |1=Xandarellida 70px |2={{clade |1=Nektaspida 70px |2={{clade |1=Conciliterga 100px |2={{clade |1=''Kwanyinaspis'' 70px |2={{clade |1=''Phytophilaspis'' 70px |2=Trilobita 100px }}}}}}}}}}}}}}}}}}|label1=Artiopoda}}

==== External phylogeny ====

Cladogram supporting the Antennulata hypothesis after Liu et al; 2026:<ref name=":03">{{Cite journal |last=Liu |first=Cong |last2=Pates |first2=Stephen |last3=Zhang |first3=Mingjing |last4=Wu |first4=Yu |last5=Ma |first5=Jiaxin |last6=Fu |first6=Dongjing |last7=Zhang |first7=Xingliang |date=2026-03-21 |title=3D morphology of the Cambrian bivalved arthropod Sunella informs about head segmentation, arthrodization, and arthropodization |url=https://www.nature.com/articles/s42003-026-09909-z |journal=Communications Biology |language=en |doi=10.1038/s42003-026-09909-z |issn=2399-3642}}</ref>{{clade|{{clade |1={{extinct}} "Lobopodia" 80 px 90 px 50 px (paraphyletic, ancestral to tardigrades, onychophorans and arthropods) |label2=Total group Euarthropoda |2={{clade |1={{extinct}}''Megadictyon'' 80 px |2={{clade |1={{clade |1={{extinct}}''Kerygmachela'' 80 px |2={{clade |1={{extinct}}''Pambdelurion'' 80 px |2={{clade |1={{extinct}}Opabiniidae 70 px |2={{clade |1={{extinct}} Radiodonta (e.g ''Anomalocaris'') 70 px |label2=Deuteropoda |2={{clade |1={{extinct}}''Erratus'' 70 px |2={{clade |1={{extinct}}''Sunella'' 70px |2={{clade |1={{extinct}}Isoxyidae 70px + "Great appendage bivalved forms" 70px |2={{clade |1={{clade |1={{extinct}}''Fengzhengia'' 80 px |2={{extinct}}''Kylinxia'' 70px }} |2={{clade |1={{extinct}}Megacheira 80px |2=Pan-Chelicerata 70px 70px }} |3={{clade |1={{extinct}}''Kiisortoqia'' 70px |2={{extinct}}''Bushizheia'' 70px |label3=Antennulata |3={{clade |1={{extinct}}Artiopoda 70px |label2=Mandibulata |2={{clade |1={{extinct}}Fuxianhuiida 70px |2={{clade |1={{extinct}}Hymenocarina 70px |2={{clade |1=Myriapoda 70px |2=Pancrustacea 70px 70px }}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}|label1=Panarthropoda|style=font-size:90%}}

==References== {{Reflist}}

{{Artiopoda}} {{Taxonbar|from=Q19842587}}

Category:Artiopoda Category:Arthropod taxa Category:Taxa described in 1997 Category:Cambrian first appearances Category:Lopingian extinctions