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{hide}automatic taxobox
| fossil_range = {{fossil range |Early Cambrian |Recent{edih}
| image = Centipede.jpg
| image_caption = A centipede (Arthropoda)
|taxon=Ecdysozoa | authority = Aguinaldo et al., 1997
| subdivision_ranks = Phyla
| subdivision =
}}Ecdysozoa ({{IPAc-en|ˌ|ɛ|k|d|ɪ|s|oʊ-|ˈ|z|oʊ|ə}}) is a group of protostome animals,JOURNAL, Telford MJ, Bourlat SJ, Economou A, Papillon D, Rota-Stabelli O, The evolution of the Ecdysozoa, Philosophical Transactions of the Royal Society B: Biological Sciences, 363, 1496, 1529–37, April 2008, 18192181, 2614232, 10.1098/rstb.2007.2243,weblink including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes.JOURNAL, Aguinaldo, A. M. A., J. M. Turbeville, L. S. Linford, M. C. Rivera, J. R. Garey, R. A. Raff, J. A. Lake, 29 May 1997, Evidence for a clade of nematodes, arthropods, and other moulting animals, Nature, 387, 489–493, 10.1038/387489a0, 9168109, 6632, 1997Natur.387R.489A, A large study in 2008 by Dunn et al. strongly supported the Ecdysozoa as a clade, that is, a group consisting of a common ancestor and all its descendants.JOURNAL, Broad phylogenomic sampling improves resolution of the animal tree of life, Nature, 452, 745–749,weblink 10.1038/nature06614, 10 April 2008, 18322464, 8, Dunn, CW, Hejnol, A, Matus, DQ, Pang, K, Browne, WE, Smith, SA, Seaver, E, Rouse, GW, Obst, M, Edgecombe, Gregory D., Sørensen, Martin V., Haddock, Steven H. D., Schmidt-Rhaesa, Andreas, Okusu, Akiko, Kristensen, Reinhardt Møbjerg, Wheeler, Ward C., Martindale, Mark Q., Giribet, Gonzalo, 7188, 2008Natur.452..745D, The group is also supported by morphological characters, and includes all animals that grow by ecdysis, moulting their exoskeleton.The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques,BOOK, Animal Evolution: Interrelationships of the Living Phyla, Claus, Nielsen, Oxford University Press, 1995, 978-0-19-850682-9, while others contested the interpretation of the molecular data.JOURNAL, Blair, J. E., Kazuho Ikeo, Takashi Gojobori, S. Blair Hedges,weblink The evolutionary position of nematodes, BMC Evolutionary Biology, 8 April 2002, 2, 7, 10.1186/1471-2148-2-7, 11985779, 102755, JOURNAL, Wägele, J. W., T. Erikson, P. Lockhart, B. Misof, December 1999, The Ecdysozoa: Artifact or monophylum?, Journal of Zoological Systematics and Evolutionary Research, 37, 4, 211–223, 10.1111/j.1439-0469.1999.tb00985.x,


{{See also|List of bilaterial animal orders}}The most notable characteristic shared by ecdysozoans is a three-layered cuticle (four in TardigradaBOOK, Barnes, Robert D., 1982, Invertebrate Zoology, Holt-Saunders International, Philadelphia, PA, 877–880, 0-03-056747-5, ) 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.JOURNAL, 10.1038/nature14573, 26106857, Hallucigenia's head and the pharyngeal armature of early ecdysozoans, Nature, 523, 7558, 75–8, 2 July 2015, Smith, Martin R., Caron, Jean-Bernard, 2015Natur.523...75S,


The Ecdysozoa include the following phyla: Arthropoda, Onychophora, Tardigrada, Kinorhyncha, Priapulida, Loricifera, Nematoda, and Nematomorpha. A few 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.Paleos Invertebrates: Panarthropoda, retrieved February 17, 2007 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. The non-panarthropod members of Ecdysozoa have been grouped as Cycloneuralia but they are more usually considered paraphyletic in as representing the primitive condition from which the Panarthropoda evolved.JOURNAL, Webster, Bonnie L., Copley, Richard R., Jenner, Ronald A., Mackenzie-Dodds, Jacqueline A., Bourlat, Sarah J., Rota-Stabelli, Omar, Littlewood, D. T. J., Telford, Maximilian J., Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan, Evolution & Development, November 2006, 8, 6, 502–510, 10.1111/j.1525-142X.2006.00123.x, A modern consensus phylogenetic tree for the protostomes is shown below.JOURNAL, Gregory D., Edgecombe, Gonzalo, Giribet, Casey W., Dunn, Andreas, Hejnol, Reinhardt M., Kristensen, Ricardo C., Neves, Greg W., Rouse, Katrine, Worsaae, Martin V., Sørensen, 10.1007/s13127-011-0044-4, Higher-level metazoan relationships: recent progress and remaining questions, June 2011, Organisms, Diversity & Evolution, 11, 2, 151–172, JOURNAL, Fröbius, Andreas C., Funch, Peter, 2017-04-04, Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans,weblink Nature Communications, 8, 1, 10.1038/s41467-017-00020-w, 2017NatCo...8....9F, JOURNAL, Smith, Martin R., Ortega-Hernández, Javier, Hallucigenia’s onychophoran-like claws and the case for Tactopoda,weblink Nature, 514, 7522, 363–366, 10.1038/nature13576, 2014, 2014Natur.514..363S, WEB,weblink Palaeos Metazoa: Ecdysozoa,, 2017-09-02, JOURNAL, Yamasaki, Hiroshi, Fujimoto, Shinta, Miyazaki, Katsumi, June 2015, Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences,weblink Zoological Letters, 1, 18, 10.1186/s40851-015-0017-0, 4657359, BOOK, Nielsen, C., Animal Evolution: Interrelationships of the Living Phyla, 2002, Oxford University Press, 2nd, 0-19-850682-1, It is indicated when approximately clades radiated into newer clades in millions of years ago (Mya); dashed lines show especially uncertain placements.JOURNAL, Peterson, Kevin J., Cotton, James A., Gehling, James G., Pisani, Davide, 2008-04-27, The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records,weblink Philosophical Transactions of the Royal Society of London B: Biological Sciences, 363, 1496, 1435–1443, 10.1098/rstb.2007.2233, 18192191, 2614224, The phylogenic tree is based on Nielsen, Nielsen, Claus, Brunet, Thibaut, Arendt, Detlev, 2018-08-22, Evolution of the bilaterian mouth and anus,weblink Nature Ecology & Evolution, 2, 9, 1358–1376, 10.1038/s41559-018-0641-0, 2397-334X, with provisional placement of Loricifera from Hiroshi et al.{{clade| style=font-size:85%;line-height:85%|label1=Bilateria|1={{clade
|1=Xenacoelomorpha (File:Proporus sp.png|60 px)
|label2=Nephrozoa |sublabel3=650 mya
|label1=Protostomia |sublabel2=610 mya
|label1=Ecdysozoa |sublabel1=>529 mya
|1=Priapulida (File:Priapulus caudatus 20150625.jpg|45 px)
|2=Kinorhyncha (File:Pycnophyes zelinkaei.jpg|35 px)
|1=Nematoda (File:CelegansGoldsteinLabUNC.jpg|60 px)
|2=Nematomorpha (File:Paragordius tricuspidatus.jpeg|60 px)
|1=Loricifera (File:Pliciloricus enigmatus.jpg|55 px)
|1=Onychophora (File:Velvet worm.jpg|60 px)
|1=Tardigrada (File:Echiniscus L.png|60 px)
|2=Arthropoda (File:Long nosed weevil edit.jpg|60 px)
|2=Spiralia (File:Grapevinesnail 01.jpg|60 px) (File:Polychaeta (no).JPG|75 px)
|2=Deuterostomia (File:Cyprinus carpio3.jpg|60 px) (File:Portugal 20140812-DSC01434 (21371237591).jpg|60 px)

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,JOURNAL, Nielsen, C, September 2003, Proposing a solution to the Articulata–Ecdysozoa controversy,weblink Zoologica Scripta, 32, 5, 475–482, 10.1046/j.1463-6409.2003.00122.x, though later considered them unrelated.BOOK, Animal Evolution: Interrelationships of the Living Phyla 3rd ed., Claus, Nielsen, Oxford University Press, 2012, 978-0-19-960603-0, Inclusion of the roundworms within the Ecdysozoa was initially contestedJOURNAL, Wägele, J. W., B. Misof, September 2001, 10.1046/j.1439-0469.2001.00177.x, On quality of evidence in phylogeny reconstruction: a reply to Zrzavý's defence of the 'Ecdysozoa' hypothesis, Journal of Zoological Systematics and Evolutionary Research, 39, 3, 165–176, but since 2003, a broad consensus has formed supporting the Ecdysozoa JOURNAL, Maximilian J Telford, D. Timothy J Littlewood, Philosophical Transactions of the Royal Society B: Biological Sciences, 27 April 2008, 363, 1421–1424, The evolution of the animals: introduction to a Linnean tercentenary celebration, 10.1098/rstb.2007.2231, 18192193, 2394567, 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.WEB,weblink The Darwin-Wallace Medal, The Linnean Society of London, 28 February 2018,

Coelomata hypothesis

Before Ecdysozoa, 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.JOURNAL, Adoutte, A., Balavoine, G., Lartillot, N., Lespinet, O., Prud'homme, B., de Rosa, R., Special Feature: The new animal phylogeny: Reliability and implications, Proceedings of the National Academy of Sciences, 25 April 2000, 97, 9, 4453–4456, 10.1073/pnas.97.9.4453,weblink 5 April 2013, 10781043, 34321, 2000PNAS...97.4453A, 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.JOURNAL, Philip, G.K., C.J. Creevey, J.O. McInerney, 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, Molecular Biology and Evolution, 9 February 2005, 22, 5, 1175–1184, 10.1093/molbev/msi102,weblink 5 April 2013, 15703245,



External links

{{Wikispecies|Ecdysozoa}} {{Animalia}}{{Taxonbar|from=Q5176}}

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