Ecdysozoa

{{Short description|Superphylum of protostomes}} {{Automatic taxobox | fossil_range = Ediacaran - Holocene, {{fossil range|560|0|ref=<ref name=uncus>{{cite journal |last1=Hughes |first1=Ian V. |last2=Evans |first2=Scott D. |last3=Droser |first3=Mary L. |title=An Ediacaran bilaterian with an ecdysozoan affinity from South Australia |journal=Current Biology |date=November 2024 |volume=34 |issue=24 |pages=5782–5788.e1 |doi=10.1016/j.cub.2024.10.030|pmid=39561775 |bibcode=2024CBio...34.5782H |doi-access=free }}</ref>}} | image = Ecdysozoa.jpg | image_caption = | display_parents = 5 | taxon = Ecdysozoa | authority = Aguinaldo ''et al''., 1997 | subdivision_ranks = Phyla | subdivision = * Scalidophora ** Kinorhyncha ** Priapulida ** Loricifera **†''Dahescolex''<ref>{{cite journal |last1=Shao |first1=T.Q. |last2=Qin |first2=J.C. |last3=Shao |first3=Y. |last4=Liu |first4=Y.H. |last5=Waloszek |first5=D. |last6=Maas |first6=A. |last7=Duan |first7=B.C. |last8=Wang |first8=Q. |last9=Xu |first9=Y. |last10=Zhang |first10=H.Q. |title=New macrobenthic cycloneuralians from the Fortunian (lowermost Cambrian) of South China |journal=Precambrian Research |date=October 2020 |volume=349 |article-number=105413 |doi=10.1016/j.precamres.2019.105413|bibcode=2020PreR..34905413S }}</ref> ** †''Dakorhachis''?<ref>{{cite journal |last1=Bekkouche |first1=Nicolas |last2=Gąsiorowski |first2=Ludwik |title=Careful amendment of morphological data sets improves phylogenetic frameworks: re-evaluating placement of the fossil Amiskwia sagittiformis |journal=Journal of Systematic Palaeontology |date=31 December 2022 |volume=20 |issue=1 |pages=1–14 |doi=10.1080/14772019.2022.2109217|url=https://hal.sorbonne-universite.fr/hal-03828531/file/Manuscript_Amiskwia_Bekkouche_and_Gasiorowski_Hall_version_compressed.pdf }}</ref> **†''Qinscolex''<ref name="qinscolex">{{cite journal |last1=Liu |first1=Yunhuan |last2=Qin |first2=Jiachen |last3=Wang |first3=Qi |last4=Maas |first4=Andreas |last5=Duan |first5=Baichuan |last6=Zhang |first6=Yanan |last7=Zhang |first7=Hu |last8=Shao |first8=Tiequan |last9=Zhang |first9=Huaqiao |title=New armoured scalidophorans (Ecdysozoa, Cycloneuralia) from the Cambrian Fortunian Zhangjiagou Lagerstätte, South China |journal=Papers in Palaeontology |date=May 2019 |volume=5 |issue=2 |pages=241–260 |doi=10.1002/spp2.1239|bibcode=2019PPal....5..241L }}</ref> **†''Shanscolex''<ref name="qinscolex"/> **†''Xinliscolex''<ref>{{cite journal |last1=Zhang |first1=Hua-Qiao |title=The evolutionary relationships of the earliest known cycloneuralians and a new record from the Cambrian Fortunian of South China |journal=Palaeoworld |date=September 2022 |volume=31 |issue=3 |pages=389–401 |doi=10.1016/j.palwor.2021.09.003}}</ref> **†''Zhongpingscolex''<ref>{{cite journal |last1=Shao |first1=T.Q. |last2=Wang |first2=Q. |last3=Liu |first3=Y.H. |last4=Qin |first4=J.C. |last5=Zhang |first5=Y.N. |last6=Liu |first6=M.J. |last7=Shao |first7=Y. |last8=Zhao |first8=J.Y. |last9=Zhang |first9=H.Q. |title=A new scalidophoran animal from the Cambrian Fortunian Stage of South China and its implications for the origin and early evolution of Kinorhyncha |journal=Precambrian Research |date=October 2020 |volume=349 |article-number=105616 |doi=10.1016/j.precamres.2020.105616|bibcode=2020PreR..34905616S }}</ref> * †Palaeoscolecida * '''Cryptovermes'''<ref name=Howard-Giacomelli-etal-2022>{{cite journal |last1=Howard |first1=Richard J. |last2=Giacomelli |first2=Mattia |last3=Lozano-Fernandez |first3=Jesus |last4=Edgecombe |first4=Gregory D. |last5=Fleming |first5=James F. |last6=Kristensen |first6=Reinhardt M. |last7=Ma |first7=Xiaoya |last8=Olesen |first8=Jørgen |last9=Sørensen |first9=Martin V. |last10=Thomsen |first10=Philip F. |last11=Wills |first11=Matthew A. |last12=Donoghue |first12=Philip C.J. |last13=Pisani |first13=Davide |display-authors=6 |date=2022-03-10 |df=dmy-all |title=The Ediacaran origin of Ecdysozoa: Integrating fossil and phylogenomic data |journal=Journal of the Geological Society |volume=179 |issue=4 |doi=10.1144/jgs2021-107 |bibcode=2022JGSoc.179..107H |s2cid=246494357 |issn=0016-7649|hdl=2445/186596 |hdl-access=free }}</ref> **Nematoida *** Nematoda *** Nematomorpha ***†''Uncus''? ** Panarthropoda *** Arthropoda *** Onychophora *** Tardigrada *** †"Lobopodia" *** †Sialomorphidae *†''Acosmia''<ref>{{cite journal |last1=Howard |first1=Richard J. |last2=Edgecombe |first2=Gregory D. |last3=Shi |first3=Xiaomei |last4=Hou |first4=Xianguang |last5=Ma |first5=Xiaoya |date=2020-11-23 |df=dmy-all |title=Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan |journal=BMC Evolutionary Biology |lang=en |volume=20 |issue=1 |page=156 |doi=10.1186/s12862-020-01720-6 |issn=1471-2148 |pmc=7684930 |pmid=33228518 |doi-access=free |bibcode=2020BMCEE..20..156H }}</ref> *†''Eolarva''<ref>{{cite journal |last1=Wang |first1=Deng |last2=Han |first2=Jian |last3=Guo |first3=Junfeng |last4=Qiang |first4=Yaqin |title=Origin and evolution of bodyplans of ecdysozoans during the Cambrian explosion |journal=Chinese Journal of Nature |date=March 2025 |volume=47 |issue=2 |pages=125-133 |doi=10.3969/j.issn.0253-9608.2025.02.004}}</ref> *†''Laojieella'' *†Saccorhytida<ref>{{cite journal |last1=Liu |first1=Yunhuan |last2=Carlisle |first2=Emily |last3=Zhang |first3=Huaqiao |last4=Yang |first4=Ben |last5=Steiner |first5=Michael |last6=Shao |first6=Tiequan |last7=Duan |first7=Baichuan |last8=Marone |first8=Federica |last9=Xiao |first9=Shuhai |display-authors=6 |date=2022-08-17 |df=dmy-all |title=Saccorhytus is an early ecdysozoan, and not the earliest deuterostome |journal=Nature |volume=609 |issue=7927 |pages=541–546 |lang=en |doi=10.1038/s41586-022-05107-z |pmid=35978194 |bibcode=2022Natur.609..541L |s2cid=251646316 |issn=1476-4687 |url=https://www.nature.com/articles/s41586-022-05107-z |hdl=1983/454e7bec-4cd4-4121-933e-abeab69e96c1 |hdl-access=free }}</ref> *†''Saccus'' }}

'''Ecdysozoa''' ({{IPAc-en|ˌ|ɛ|k|d|ɪ|s|oʊ-|ˈ|z|oʊ|ə}}) is a group of protostome animals,<ref name="TelfordBourlat2008">{{cite journal |last1=Telford |first1=Maximilian J. |last2=Bourlat |first2=Sarah J. |last3=Economou |first3=Andrew |last4=Papillon |first4=Daniel |last5=Rota-Stabelli |first5=Omar |year=2008 |title=The evolution of the Ecdysozoa |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=363 |issue=1496 |pages=1529–1537 |issn=0962-8436 |doi=10.1098/rstb.2007.2243 |pmid=18192181 |pmc=2614232 }}</ref> including Arthropoda (insects, chelicerates (including arachnids), crustaceans, and myriapods), Nematoda, and several smaller phyla. The grouping of these animal phyla into a single clade was first proposed by Eernisse ''et al.'' (1992) based on a phylogenetic analysis of 141 morphological characters of ultrastructural and embryological phenotypes.<ref>{{cite journal |last1=Eernisse |first1=D.J. |last2=Albert |first2=J.S. |last3=Anderson |first3=F.E. | year=1992 |title=Annelida and Arthropoda are not sister taxa: A phylogenetic analysis of spiralian metazoan morphology |journal=Systematic Biology |volume=41 |issue=3 |pages=305–330 |doi= 10.1093/sysbio/41.3.305 }}</ref> This clade, that is, a group consisting of a common ancestor and all its descendants, was formally named by Aguinaldo ''et al.'' in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes.<ref>{{cite journal |last1=Aguinaldo |first1=A.M.A. |first2=J.M. |last2=Turbeville |first3=L.S. |last3=Linford |first4=M.C. |last4=Rivera |first5=J.R. |last5=Garey |first6=R.A. |last6=Raff |first7=J.A. |last7=Lake |date=29 May 1997 |title=Evidence for a clade of nematodes, arthropods, and other moulting animals |journal=Nature |volume=387 |pages=489–493 |doi=10.1038/387489a0 |pmid=9168109 |issue=6632 |bibcode=1997Natur.387R.489A |s2cid=4334033 }}</ref>

A large study in 2008 by Dunn ''et al.'' strongly supported the monophyly of Ecdysozoa.<ref name=nature_phylo>{{cite journal |last1=Dunn |first1=C.W. |last2=Hejnol |first2=A. |last3=Matus |first3=D.Q. |last4=Pang |first4=K. |last5=Browne |first5=W.E. |last6=Smith |first6=S.A. |last7=Seaver |first7=E. |last8=Rouse |first8=G.W. |last9=Obst |first9=M. |last10=Edgecombe |first10=Gregory D. |last11=Sørensen |first11=Martin V. |last12=Haddock |first12=Steven H.D. |last13=Schmidt-Rhaesa |first13=Andreas |last14=Okusu |first14=Akiko |last15=Kristensen |first15=Reinhardt Møbjerg |last16=Wheeler |first16=Ward C. |last17=Martindale |first17=Mark Q. |last18=Giribet |first18=Gonzalo |display-authors=6 |date=10 April 2008 |title=Broad phylogenomic sampling improves resolution of the animal tree of life |journal=Nature |volume=452 |issue=7188 |pages=745–749 |doi=10.1038/nature06614 |pmid=18322464 |bibcode=2008Natur.452..745D|s2cid=4397099 }}</ref>

The group Ecdysozoa is supported by many morphological characters, including growth by ecdysis, with moulting of the cuticle – without mitosis in the epidermis – under control of the prohormone ecdysone, and internal fertilization.<ref>{{cite book |last=Ax |first=P. |year=1985 |section=The position of the Gnathostomulida and Platyhelminthes in the phylogenetic system of the Bilateria |editor1=Conway Morris, S. |editor2=George, J.D. |editor3=Gibson, R. |editor4=Platt, H.M. |title=The Origins and Relationships of Lower Invertebrates |series=Systematics Association Special Volume |volume=28 |place=New York, NY |publisher=Clarendon / Oxford University Press |isbn=0-19-857181-X |oclc=59186778 |pages=168–180 |quote=proceedings of an international symposium held in London, September 1983 |url=https://archive.org/details/originsrelations0000unse |via=Internet Archive (archive.org)}} {{ISBN|9780198571810}}</ref>

The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques,<ref>{{cite book |first=Claus |last=Nielsen |year=1995 |title=Animal Evolution: Interrelationships of the living phyla |publisher=Oxford University Press |isbn=978-0-19-850682-9}}</ref> while others contested the interpretation of the molecular data.<ref name=Blair>{{cite journal |first1=J.E. |last1=Blair |first2=Kazuho |last2=Ikeo |first3=Takashi |last3=Gojobori |first4=S. Blair |last4=Hedges |date=8 April 2002 |title=The evolutionary position of nematodes |journal=BMC Evolutionary Biology |volume=2 |page=7 |doi=10.1186/1471-2148-2-7 |pmid=11985779 |pmc=102755 |doi-access=free }}</ref><ref>{{cite journal |first1=J.W. |last1=Wägele |first2=T. |last2=Erikson |first3=P. |last3=Lockhart |first4=B. |last4=Misof |date=December 1999 |title=The Ecdysozoa: Artifact or monophylum? |journal=Journal of Zoological Systematics and Evolutionary Research |volume=37 |issue=4 |pages=211–223 |doi=10.1111/j.1439-0469.1999.tb00985.x|doi-access=free }}</ref>

== Etymology == The name ''Ecdysozoa'' is scientific Greek, derived from {{math|ἔκδυσις}} (''{{grc-transl|ἔκδυσις}}'') "shedding" + {{math|ζῷον}} (''{{grc-transl|ζῷον}}'') "animal".

== Characteristics == {{See also|List of bilaterial animal orders}}

The most notable characteristic shared by ecdysozoans is a three-layered cuticle (four in Tardigrada<ref>{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA |pages= 877–880 |isbn=0-03-056747-5}}</ref>) composed of organic material, which is periodically molted as the animal grows. This process of molting is called ecdysis, and gives the group its name. The ecdysozoans lack locomotory cilia and produce mostly amoeboid sperm, and their embryos do not undergo spiral cleavage as in most other protostomes. Ancestrally, the group exhibited sclerotized teeth within the foregut, and a ring of spines around the mouth opening, though these features have been secondarily lost in certain groups.<ref>{{cite journal |last1=Smith |first1=Martin R. |last2=Caron |first2=Jean-Bernard |date=2 July 2015 |title=Hallucigenia's head and the pharyngeal armature of early ecdysozoans |journal=Nature |volume=523 |issue=7558 |pages=75–78 |bibcode=2015Natur.523...75S |s2cid=205244325 |doi=10.1038/nature14573 |pmid=26106857 |url=http://dro.dur.ac.uk/20476/1/20476.pdf}}</ref><ref>{{cite journal | url=https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12256 | doi=10.1111/pala.12256 | title=The mouth apparatus of the Cambrian gilled lobopodian ''Pambdelurion whittingtoni'' | date=2016 | last1=Vinther | first1=Jakob | last2=Porras | first2=Luis | last3=Young | first3=Fletcher J. | last4=Budd | first4=Graham E. | last5=Edgecombe | first5=Gregory D. | journal=Palaeontology | volume=59 | issue=6 | pages=841–849 | bibcode=2016Palgy..59..841V | hdl=1983/16da11f1-5231-4d6c-9968-69ddc5633a8a | hdl-access=free }}</ref> An unpaired ventral nerve cord, present in Priapulida and Nematoida, appear to be the ancestral condition, making the paired ventral nerve cord found in Panarthropoda, Kinorhyncha and Loricifera a derived trait.<ref>{{cite journal | last1=Wang | first1=Deng | last2=Vannier | first2=Jean | last3=Martín-Durán | first3=José M. | last4=Herranz | first4=María | last5=Yu | first5=Chiyang | title=Preservation and early evolution of scalidophoran ventral nerve cord | journal=Science Advances | date=2025 | volume=11 | issue=2 | article-number=eadr0896 | doi=10.1126/sciadv.adr0896 | pmid=39792685 | pmc=11721716 | bibcode=2025SciA...11R.896W }}</ref> A respiratory and circulatory system is only present in onychophorans and arthropods (often absent in smaller arthropods like mites); in the rest of the groups, both systems are missing. Ecdysozoans rely exclusively on the arginine phosphate/arginine kinase (AP/AK) system, a high-energy phosphate system used to regenerate ATP from ADP. In contrast, vertebrates use only the creatine phosphate/creatine kinase (CP/CK) system, while some other invertebrates may employ both systems.<ref>{{Cite journal |last1=Lukić-Bilela |first1=Lada |last2=Perović-Ottstadt |first2=Sanja |last3=Walenta |first3=Stefan |last4=Natalio |first4=Filipe |last5=Pleše |first5=Bruna |last6=Link |first6=Thorben |last7=Müller |first7=Werner E. G. |title=ATP distribution and localization of mitochondria in ''Suberites domuncula'' (Olivi 1792) tissue |journal=Journal of Experimental Biology |date=2011 |volume=214 |issue=10 |pages=1748–1753 |doi=10.1242/jeb.053439 |pmid=21525322 |bibcode=2011JExpB.214.1748L |doi-access=free}}</ref><ref>{{cite journal | last1=Deligio | first1=J.T. | last2=Ellington | first2=W.R. | title=The capacity for the de novo biosynthesis of creatine is present in the tunicate Ciona intestinalis and is likely widespread in other protochordate and invertebrate groups | journal=Comparative Biochemistry and Physiology Part D: Genomics and Proteomics | date=2006 | volume=1 | issue=2 | pages=167–178 | doi=10.1016/j.cbd.2005.08.006 | pmid=20483248 | url=https://www.sciencedirect.com/science/article/abs/pii/S1744117X05000122 | url-access=subscription }}</ref>

== Phylogeny ==

The Ecdysozoa include the following phyla: Arthropoda, Onychophora, Tardigrada, Kinorhyncha, Priapulida, Loricifera, Nematoda, and Nematomorpha. A few extinct taxa have been classified as stem group ecdysozoans, such as ''Uncus dzaugisi'' and ''Acosmia''. Other groups such as the gastrotrichs, have been considered possible members but lack the main characters of the group, and are now placed elsewhere. The Arthropoda, Onychophora, and Tardigrada have been grouped together as the Panarthropoda because they are distinguished by segmented body plans.<ref>{{cite web |title=Panarthropoda |website=Paleos (palaeos.com) |series=Invertebrates |url=http://www.palaeos.com/Invertebrates/Arthropods/Panarthropoda.html |access-date=17 February 2007 |archive-url=https://web.archive.org/web/20070207102301/http://www.palaeos.com/Invertebrates/Arthropods/Panarthropoda.html |archive-date=2007-02-07 }}</ref> Dunn ''et al.'' in 2008 suggested that the tardigrada could be grouped along with the nematodes, leaving Onychophora as the sister group to the arthropods.<ref name="nature_phylo" /> The non-panarthropod members of Ecdysozoa have been grouped as Cycloneuralia but they are more usually considered paraphyletic in representing the primitive condition from which the Panarthropoda evolved.<ref>{{cite journal |last1=Webster |first1=Bonnie L. |last2=Copley |first2=Richard R. |last3=Jenner |first3=Ronald A. |last4=Mackenzie-Dodds |first4=Jacqueline A. |last5=Bourlat |first5=Sarah J. |last6=Rota-Stabelli |first6=Omar |last7=Littlewood |first7=D.T.J. |last8=Telford |first8=Maximilian J. |display-authors=6 |date=November 2006 |title=Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan |journal=Evolution & Development |volume=8 |issue=6 |pages=502–510 |doi=10.1111/j.1525-142X.2006.00123.x |pmid=17073934 |s2cid=22823313}}</ref>

A modern consensus phylogenetic tree for the protostomes is shown below.<ref>{{cite journal |first1=Gregory D. |last1=Edgecombe |first2=Gonzalo |last2=Giribet |first3=Casey W. |last3=Dunn |first4=Andreas |last4=Hejnol |first5=Reinhardt M. |last5=Kristensen |first6=Ricardo C. |last6=Neves |first7=Greg W. |last7=Rouse |first8=Katrine |last8=Worsaae |first9=Martin V. |last9=Sørensen |display-authors=6 |date=June 2011 |title=Higher-level metazoan relationships: Recent progress and remaining questions |journal=Organisms, Diversity & Evolution |volume=11 |issue=2 |pages=151–172 |s2cid=32169826 |doi=10.1007/s13127-011-0044-4 |bibcode=2011ODivE..11..151E |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:27755241 |url-access=subscription }}</ref><ref name=Fröbius>{{Cite journal |last1=Fröbius |first1=Andreas C. |last2=Funch |first2=Peter |date=2017-04-04 |df=dmy-all |title=Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans |journal=Nature Communications |volume=8 |issue=1 |page=9 |doi=10.1038/s41467-017-00020-w |pmid=28377584 |pmc=5431905 |bibcode=2017NatCo...8....9F }}</ref><ref>{{cite journal |last1=Smith |first1=Martin R. |last2=Ortega-Hernández |first2=Javier |year=2014 |title=Hallucigenia's onychophoran-like claws and the case for Tactopoda |journal=Nature |volume=514 |issue=7522 |pages=363–366 |doi=10.1038/nature13576 |pmid=25132546 |bibcode=2014Natur.514..363S |s2cid=205239797 |url=http://dro.dur.ac.uk/19108/1/19108.pdf}}</ref><ref name="Palaeos Metazoa: Ecdysozoa">{{Cite web |url=http://palaeos.com/metazoa/ecdysozoa/ecdysozoa.html |title=Palaeos Metazoa: Ecdysozoa |website=palaeos.com |access-date=2017-09-02}}</ref><ref>{{cite journal |last1=Yamasaki |first1=Hiroshi |last2=Fujimoto |first2=Shinta |last3=Miyazaki |first3=Katsumi |date=June 2015 |title=Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences |journal=Zoological Letters |volume=1 |page=18 |doi=10.1186/s40851-015-0017-0|pmid=26605063 |pmc=4657359 |doi-access=free }}</ref><ref>{{cite book |last=Nielsen |first=C. |year=2002 |title=Animal Evolution: Interrelationships of the Living Phyla |publisher=Oxford University Press |edition=2nd |isbn=0-19-850682-1}}</ref> It is indicated when approximately clades radiated into newer clades in millions of years ago (Mya); dashed lines show especially uncertain placements.<ref>{{cite journal |last1=Peterson |first1=Kevin J. |last2=Cotton |first2=James A. |last3=Gehling |first3=James G. |last4=Pisani |first4=Davide |date=2008-04-27 |df=dmy-all |title=The Ediacaran emergence of bilaterians: Congruence between the genetic and the geological fossil records |journal=Philosophical Transactions of the Royal Society of London B: Biological Sciences |volume=363 |issue=1496 |pages=1435–1443 |doi=10.1098/rstb.2007.2233 |pmid=18192191 |pmc=2614224}}</ref>

The phylogenetic tree is based on Nielsen ''et al.''<ref>{{cite journal |last1=Nielsen |first1=Claus |last2=Brunet |first2=Thibaut |last3=Arendt |first3=Detlev |date=2018-08-22 |title=Evolution of the bilaterian mouth and anus |journal=Nature Ecology & Evolution |volume=2 |issue=9 |pages=1358–1376 |doi=10.1038/s41559-018-0641-0 |pmid=30135501 |bibcode=2018NatEE...2.1358N |s2cid=52067372 |issn=2397-334X }}</ref> and Howard ''et al.''.<ref name=Howard-Giacomelli-etal-2022/>

{{clade| style=font-size:85%;line-height:85% |label1=Bilateria |1={{clade |1=Xenacoelomorpha 60 px |label2=Nephrozoa|sublabel3=650 mya |2={{clade |1=Deuterostomia 60 px 60 px |label2=Protostomia |sublabel2=610 mya |2={{clade |label1='''Ecdysozoa'''|sublabel1= |1={{clade |label1=Scalidophora |1={{clade |label1= |1=Loricifera 55 px |2={{clade |label1= |1=Priapulida 45 px |2=Kinorhyncha 35 px }} }} |label2=Cryptovermes |2={{clade |label1=Nematoida |1={{clade |label1= |1=Nematoda 60 px |2=Nematomorpha 60 px }} |label2=Panarthropoda |2={{clade |1=Tardigrada 60 px |label2=Antennopoda |2={{clade |label1= |1=Onychophora 60 px |2=Arthropoda 60 px }}

}} }} }} |2=Spiralia 60 px 75 px |3=''Kimberella'' † }} }} }} }}

== Older alternative groupings ==

=== Articulata hypothesis === The grouping proposed by Aguinaldo ''et al.'' is almost universally accepted, replacing an older hypothesis that Panarthropoda should be classified with Annelida in a group called the Articulata, and that Ecdysozoa are polyphyletic. Nielsen has suggested that a possible solution is to regard Ecdysozoa as a sister-group of Annelida,<ref>{{cite journal | last1 = Nielsen | first1 = C. | date = September 2003 | title = Proposing a solution to the Articulata–Ecdysozoa controversy | journal = Zoologica Scripta | volume = 32 | issue = 5| pages = 475–482 | s2cid = 1416582 | doi=10.1046/j.1463-6409.2003.00122.x}}</ref> though later considered them unrelated.<ref>{{cite book |first=Claus |last=Nielsen |year=2012 |title=Animal Evolution: Interrelationships of the living phyla |edition=3rd |publisher=Oxford University Press |isbn=978-0-19-960603-0}}</ref> Inclusion of the roundworms within the Ecdysozoa was initially contested<ref name=Blair/><ref>{{cite journal |last=Zrzavý |first=J. |date=12 January 2002 |title=Ecdysozoa versus Articulata: Clades, artifacts, prejudices |journal=Journal of Zoological Systematics and Evolutionary Research |volume=39 |issue=3 |pages=159–163 |doi=10.1046/j.1439-0469.2001.00168.x|doi-access=free }} — in support of clade Ecdysozoa</ref><ref>{{cite journal |last1=Wägele |first1=J.W. |first2=B. |last2=Misof |date=September 2001 |title=On quality of evidence in phylogeny reconstruction: A reply to Zrzavý's defence of the 'Ecdysozoa' hypothesis |journal=Journal of Zoological Systematics and Evolutionary Research |volume=39 |issue=3 |pages=165–176 |doi=10.1046/j.1439-0469.2001.00177.x|doi-access=free }}</ref> but since 2003, a broad consensus has formed supporting the Ecdysozoa<ref>{{cite journal |first1=Maximilian J. |last1=Telford |first2=D. Timothy J. |last2=Littlewood |date=27 April 2008 |title=The evolution of the animals: Introduction to a Linnean tercentenary celebration |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=363 |issue=1496 |pages=1421–1424 |doi=10.1098/rstb.2007.2231 |pmid=18192193 |pmc=2394567}}</ref> and in 2011 the Darwin–Wallace Medal was awarded to James Lake for the discovery of the New Animal Phylogeny consisting of the Ecdysozoa, the Lophotrochozoa, and the Deuterostomia.<ref name="Darwin–Wallace Medal">{{cite press release |title=The Darwin-Wallace Medal |publisher=The Linnean Society of London |url=https://www.linnean.org/the-society/medals-awards-prizes-grants/the-darwin-wallace-medal |access-date=28 February 2018}}</ref>

=== Coelomata hypothesis ===

Before Aguinaldo's Ecdysozoa proposal, one of the prevailing theories for the evolution of the bilateral animals was based on the morphology of their body cavities. There were three types, or grades of organization: the Acoelomata (no coelom), the Pseudocoelomata (partial coelom), and the Eucoelomata (true coelom). Adoutte and coworkers were among the first to strongly support the Ecdysozoa.<ref>{{cite journal |last1=Adoutte |first1=A. |author2=Balavoine, G. |author3=Lartillot, N. |author4=Lespinet, O. |author5=Prud'homme, B. |author6=de Rosa, R. |date=25 April 2000 |title=The new animal phylogeny: Reliability and implications |department=Special feature |journal=Proceedings of the National Academy of Sciences of the USA |volume=97 |issue=9 |pages=4453–4456 |doi=10.1073/pnas.97.9.4453 |doi-access=free |pmid=10781043 |pmc=34321 |bibcode=2000PNAS...97.4453A }}</ref> With the introduction of molecular phylogenetics, the coelomate hypothesis was abandoned, although some molecular, phylogenetic support for the Coelomata continued until as late as 2005.<ref>{{cite journal |first1=G.K. |last1=Philip |first2=C.J. |last2=Creevey |first3=J.O. |last3=McInerney |date=9 February 2005 |title=The Opisthokonta and the Ecdysozoa may not be clades: Stronger support for the grouping of plant and animal than for animal and fungi, and stronger support for the Coelomata than Ecdysozoa |journal=Molecular Biology and Evolution |volume=22 |issue=5 |pages=1175–1184 |doi=10.1093/molbev/msi102 |doi-access=free |pmid=15703245}}</ref>

==References==  {{reflist|25em}}

== Further reading == * {{Cite conference |first1=James R. |last1=Garey |first2=Andreas |last2=Schmidt-Rhaesa |date=December 1998 |orig-date=3–7 January 1998 |title=Essential Role of 'Minor' Phyla in Understanding Animal Evolution |conference=Symposium on Evolutionary Relationships of Metazoan Phyla: Advances, Problems, and Approaches (Annual Meeting of the Society for Integrative and Comparative Biology) |location=Boston, Massachusetts |journal=American Zoologist |volume=38 |issue=6 |pages=907–917 |doi=10.1093/icb/38.6.907 |jstor=4620218 |via=chuma.cas.usf.edu/~garey |url=http://chuma.cas.usf.edu/~garey/essential.html |access-date=2023-07-30 |archive-url=https://web.archive.org/web/20030313065540/http://chuma.cas.usf.edu/~garey/essential.html |archive-date=2003-03-13 |doi-access=free }} * {{Cite journal |first1=Andreas |last1=Schmidt-Rhaesa |first2=Thomas |last2=Bartolomaeus |first3=Christian |last3=Lemburg |first4=Ulrich |last4=Ehlers |first5=James R. |last5=Garey |date=December 1998 |orig-date=6 January 1999 (online publication) |title=The Position of the Arthropoda in the phylogenetic system |journal=Journal of Morphology |volume=238 |issue=3 |pages=263–285 |doi=10.1002/(SICI)1097-4687(199812)238:3<263::AID-JMOR1>3.0.CO;2-L|pmid=29852696 |s2cid=46920478 }} ** {{cite web |title=Abstract & images |website=chuma.cas.usf.edu/~garey |url=http://chuma.cas.usf.edu/~garey/articulata.html |archive-url=https://web.archive.org/web/20100510081324/http://chuma.cas.usf.edu/~garey/articulata.html |archive-date=2010-05-10 }}

== External links == {{Wikispecies|Ecdysozoa}} * {{Cite web |title=Ecdysozoa introduction |url=http://www.ucmp.berkeley.edu/phyla/ecdysozoa.html |department=Phyla |publisher=University of California Museum of Paleontology (ucmp.berkeley.edu) |place=Berkeley, CA}} * {{Cite web |title=Ecdysozoa |url=http://www.palaeos.com/Kingdoms/Animalia/Ecdysozoa.html |archive-url=https://web.archive.org/web/20030313115747/http://www.palaeos.com/Kingdoms/Animalia/Ecdysozoa.html |archive-date=2003-03-13 |department=Kingdoms / Animalia |website=palaeos.com}} * {{Cite web |title=Tardigrades and Ecdysozoa |department=Tardigrades |website=nematodes.org |url=http://www.nematodes.org/tardigrades/Tardigrades_and_Ecdysozoa.html |archive-url=https://web.archive.org/web/20080618211750/http://www.nematodes.org/tardigrades/Tardigrades_and_Ecdysozoa.html |archive-date=2008-06-18 }} * [http://www.nematomorpha.net Nematomorpha]

Category:Ecdysozoa Category:Extant Cambrian first appearances Category:Superphyla