{{Short description|Clade of arthropods}} {{Automatic taxobox | fossil_range = {{fossilrange|Cambrian|Present}} | image = 20210310 Kylinxia zhangi.png | image_caption = Life restoration of ''Kylinxia zhangi'', a basal deuteropod | taxon = Deuteropoda | authority = Ortega-Hernández 2016<ref name="Ortega-Hernández"/> | subdivision_ranks = Subphyla and classes | subdivision = *†''Burgessia'' *†''Bushizheia'' *†''Cucumericrus''?<ref name="McCall2023">{{cite journal |last1=McCall |first1=Christian |title=A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada |journal=Journal of Paleontology |date=13 December 2023 |doi=10.1017/jpa.2023.63 |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/large-pelagic-lobopodian-from-the-cambrian-pioche-shale-of-nevada/11B0704C49A7730AA3E8F46EB2CA1C95 |access-date=13 December 2023|url-access=subscription }}</ref> *†''Erratus'' *†''Fengzhengia'' *†''Forfexicaris'' *†''Kiisortoqia'' *†''Kylinxia'' *†''Occacaris'' *†''Oreinorema'' *†''Oura'' *†''Sarotrocercus'' *†'''Artiopoda''' (including Trilobita) *†'''Fuxianhuiida''' *†'''Isoxyida''' *†'''Marrellomorpha''' *†'''Megacheira''' *'''Chelicerata''' *'''Mandibulata''' | image2 = Surusicaris reconstruction.png | image2_caption = Life restoration of ''Surusicaris'' (Isoxyidae), a likely basal deuteropod }}
'''Deuteropoda''' is a clade of arthropods whose members are distinguished from more basal stem-group arthropods like radiodonts by an anatomical reorganization of the head region (which is proposed to include a differentiated, titular "deutocerebral" first appendage pair, a multisegmented head, and a hypostome/labrum complex), and by bearing pairs of segmented biramous (two branched) limbs.<ref name="Ortega-Hernández">{{Citation| last1 = Ortega-Hernández| first1 = Javier| title = Making sense of 'lower' and 'upper' stem-group Euarthropoda, with comments on the strict use of the name Arthropoda von Siebold, 1848| journal = Biol. Rev.| volume = 91| pages = 255–273|pmid=25528950 |s2cid=7751936 | year = 2016| issue = 1| doi = 10.1111/brv.12168}}</ref>
The clade contains all living arthropods (i.e. chelicerates and mandibulates) as well as several fossil groups that share these characteristics (e.g. Fuxianhuiida, Megacheira, Isoxyida, and Artiopoda, the last of which includes the trilobites), while excluding other fossil groups that are more 'basal' or 'primitive' (e.g. radiodonts, opabiniids and lobopodians).<ref name="Ortega-Hernández" /><ref name="GrahamBudd2021">{{cite journal|first1=Graham E.|last1=Budd|title=The origin and evolution of the euarthropod labrum|date=2021|doi=10.1016/j.asd.2021.101048|issn=1467-8039|volume=62|article-number=101048|journal=Arthropod Structure & Development|pmid=33862532 |doi-access=free}}</ref> Members of Deuteropoda that are basal to the last common ancestor of chelicerates and mandibulates (and thus lie outside the crown group of Arthropoda) are often referred to as '''"upper stem group arthropods"'''.<ref name="Ortega-Hernández" /><ref name=":2" />
==Defining characteristics== [[File:Figure 3. Morphological reconstruction and phylogenetic position of Isoxys curvirostratus (cropped).jpg|thumb|Diagram of primitive deuteropod ''Isoxys curvirostratus'' showing upward-curling grasping first appendage as well as two branched (biramous) limbs consisting of an inner endopod and outer exopod, as is characteristic of Deuteropoda.|left]] Javier Ortega-Hernández in his 2016 study naming the clade, proposed that Deuteropoda is differentiated from more basal total group arthropods by the presence of a differentiated labrum (part of the mouth) and a differentiated first pair of appendages innervated by a part of the brain called the deutocerebrum (making them "deutocerebral").<ref name="Ortega-Hernández" /> In contrast, lobopodians (part of the "lower stem group") and onychophorans have a pair of pre-ocular (located in front of the eyes) appendages innervated by a part of the brain called the protocerebrum (making them "protocerebral"), which has been proposed by a number of authors to have evolved to be the labrum of modern living arthropods, and to be homologous (derived from the same ancestral structure) to the segmented frontal appendages of radiodonts, which these authors argue was protocerebral.<ref name="GrahamBudd2021" /> In living arthropods, the deutocerebral appendage corresponds to the first pair of antennae in mandibulates and the chelicerae in chelicerates.<ref name=":3">{{Cite journal |last=Lev |first=Oren |last2=Edgecombe |first2=Gregory D |last3=Chipman |first3=Ariel D |date=2022-05-24 |title=Serial Homology and Segment Identity in the Arthropod Head |url=https://academic.oup.com/iob/article/doi/10.1093/iob/obac015/6571934 |journal=Integrative Organismal Biology |language=en |volume=4 |issue=1 |doi=10.1093/iob/obac015 |issn=2517-4843 |pmc=9128542 |pmid=35620450}}</ref> All deuteropods are suggested to have a multi-segmented head with at least three segments including the protocerebrum, deutocerebrum and tritocerebrum (the head in non-deuteropodan stem-group arthropods including radiodonts is generally suggested in contrast to have been composed of a single segment including the protocerebrum).<ref name=":3" />
While the clade comprising Deuteropoda (though not necessarily the name itself) is well accepted, the characters Ortega-Hernández proposed as supporting Deuteropoda are somewhat controversial, with number of authors arguing that the transformation of the head from radiodonts to early deuteropods is less radical than proposed,<ref name=":2" /> and argue that there is no clear evidence of a switch between a protocerebral head appendage in radiodonts to a deutocerebral one in Deuteropoda,<ref>{{Cite journal |last=Aria |first=Cédric |date=29 May 2019 |title=Reviewing the bases for a nomenclatural uniformization of the highest taxonomic levels in arthropods |url=https://www.cambridge.org/core/product/identifier/S0016756819000475/type/journal_article |journal=Geological Magazine |language=en |volume=156 |issue=08 |pages=1463–1468 |doi=10.1017/S0016756819000475 |issn=0016-7568}}</ref> with some authors arguing that brains of radiodonts were two-segmented rather than single segmented and that their frontal appendages were in fact deutocerebral,<ref>{{Cite journal |last=Moysiuk |first=Joseph |last2=Caron |first2=Jean-Bernard |date=2022-08-08 |title=A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation |url=https://www.cell.com/current-biology/abstract/S0960-9822(22)00986-1 |journal=Current Biology |language=English |volume=32 |issue=15 |pages=3302–3316.e2 |doi=10.1016/j.cub.2022.06.027 |issn=0960-9822 |pmid=35809569}}</ref> or that the first appendages of early deuteropodans were in fact protocerebral.<ref>{{Cite journal |last=Aria |first=Cédric |last2=Caron |first2=Jean-Bernard |date=2015-06-03 |editor-last=Friedman |editor-first=Matt |title=Cephalic and Limb Anatomy of a New Isoxyid from the Burgess Shale and the Role of “Stem Bivalved Arthropods” in the Disparity of the Frontalmost Appendage |url=https://dx.plos.org/10.1371/journal.pone.0124979 |journal=PLOS ONE |language=en |volume=10 |issue=6 |pages=e0124979 |doi=10.1371/journal.pone.0124979 |issn=1932-6203 |pmc=4454494 |pmid=26038846}}</ref>
Many early primitive deuteropod first appendages like those in ''Kylinxia'' and isoxyids are segmented grasping appendages that are upward (dorsally)-curling, as opposed to downward curling like the frontal appendages of radiodonts, which may represent a shared ancestral trait for most or all of Deuteropoda. It is disputed whether or not the upward-curling grasping appendage of early deuteropods are homologous to the frontal appendage of radiodonts, to which they show strong structural similarities, or that they were convergently evolved separately.<ref name=":1" />
Members of Deuteropoda lack the oral cone mouth present in radiodonts, but instead ancestrally possess a posteriorly facing mouth on the underside of the head, which is at least sometimes covered by a hypostome.<ref name=":2">{{Cite journal |last=Liu |first=Yu |last2=O’Flynn |first2=Robert J. |last3=Yu |first3=Mengxiao |last4=Mai |first4=Huijuan |last5=Hou |first5=Xianguang |last6=Edgecombe |first6=Gregory D. |date=May 2026 |title=A transitional, early Cambrian species bridges radiodonts and upper stem-group euarthropods |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982226005786 |journal=Current Biology |language=en |doi=10.1016/j.cub.2026.05.002}}</ref> Another distinctive characteristic ancestrally present in deuteropodans (with the exception of the radiodont-like ''Oreinorema''<ref name=":2" />) but not more basal stem-arthropods is the presence of two-branched (biramous) segmented (arthropodized) limbs running along the body posterior to the mouth, distinct from the swimming flaps present in radiodonts and "gilled lobopodians" and the lobopods of lobopodians,<ref name="Ortega-Hernández" /><ref name=":1" /> though the appendages of many modern arthropods are secondarily uniramous (unbranched).<ref>{{Cite journal |last=Dworkin |first=Ian M. |last2=Tanda |first2=Soichi |last3=Larsen |first3=Ellen |date=November 2001 |title=Are entrenched characters developmentally constrained? Creating biramous limbs in an insect |url=https://onlinelibrary.wiley.com/doi/10.1046/j.1525-142X.2001.01047.x |journal=Evolution & Development |language=en |volume=3 |issue=6 |pages=424–431 |doi=10.1046/j.1525-142X.2001.01047.x |issn=1520-541X|url-access=subscription }}</ref><ref>{{Cite journal |last=Lustri |first=Lorenzo |last2=Gueriau |first2=Pierre |last3=Daley |first3=Allison C. |date=2024-05-07 |title=Lower Ordovician synziphosurine reveals early euchelicerate diversity and evolution |url=https://www.nature.com/articles/s41467-024-48013-w |journal=Nature Communications |language=en |volume=15 |issue=1 |doi=10.1038/s41467-024-48013-w |issn=2041-1723 |pmc=11076625 |pmid=38714651}}</ref> The segmentation of the body limbs may have evolved from the co-option of the genes causing the segmentation of the first head appendage in the Deuteropoda-Radiodonta common ancestor.<ref name=":3" /> Most deuteropods (with the exception of ''Erratus'' and isoxyids, and secondarily some modern arthropods) also have a segmented and jointed (arthrodized) trunk (main body section),<ref name=":1" /> ==Phylogeny== The cladogram below is a possible panarthropod phylogeny, taking into account the differentiation between "lower stem group arthropods" (Total group Euarthropoda) and "upper stem group arthropods" (Deuteropoda), based on a phylogenetic analysis published in 2026.<ref name=":1">{{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|doi-access=free }}</ref> Not all parts of this cladogram are universally accepted, as some other studies have found a closer relationship to Chelicerata than to Mandibulata for Artiopoda,<ref name=":0">{{Cite journal |last=Aria |first=Cédric |date=October 2022 |title=The origin and early evolution of arthropods |url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12864 |journal=Biological Reviews |language=en |volume=97 |issue=5 |pages=1786–1809 |doi=10.1111/brv.12864 |pmid=35475316 |s2cid=243269510 |issn=1464-7931|url-access=subscription }}</ref> and for Megacheira to be outside crown-group Arthropoda.<ref name=":0" /> {{Clear}}{{clade |label1=Panarthropoda |1={{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 (including Trilobita) 70px |label2=Mandibulata |2={{clade |1={{extinct}}Fuxianhuiida 70px |2={{clade |1={{extinct}}Hymenocarina 70px |2={{clade |1=Myriapoda 70px |2=Pancrustacea 70px 70px }}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}|style=font-size:90%}}
==References== {{Reflist}}
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Category:Ecdysozoa unranked clades Category:Arthropod taxonomy