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Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Ecdysozoa
Cladi: Cycloneuralia – Panarthropoda
Overview of phyla: ArthropodaKinorhyncha (cladus) – LoriciferaNematodaNematomorphaOnychophoraPriapulidaTardigrada


Ecdysozoa Aguinaldo et al., 1997

Aguinaldo, A.M., Turbeville, J.M., Linford, L.S., Rivera, M.C., Garey, J.R., Raff, R.A. & Lake, J.A. 1997. Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 387: 489–93. DOI: 10.1038/387489a0
Garey, J.R. 2001. Ecdysozoa: the relationship between Cycloneuralia and Panarthropoda. Zoologischer Anzeiger 240: 321–330.
Park, J.-K., Rho, H.S., Kristensen, R.M., Kim, W. & Giribet, G. 2006. First Molecular Data on the Phylum Loricifera – An Investigation into the Phylogeny of Ecdysozoa with Emphasis on the Positions of Loricifera and Priapulida. Zoological science 23: 943–954. DOI: 10.2108/zsj.23.943
Petrov, N.B. & Vladychenskaya, N.S. 2005. Phylogeny of protostome moulting animals (Ecdysozoa) inferred from 18 and 28S rRNA gene sequences. Molecular biology (Moscow) 39(4): 503-513.
Podsiadlowski, L., Braband, A. & Mayer, G. 2008. The complete mitochondrial genome of the onychophoran Epiperipatus biolleyi reveals a unique transfer RNA set and provides further support for the Ecdysozoa hypothesis. Molecular biology and evolution 25(1): 42–51. Online.
Sørensen, M.V., Hebsgaard, M.B., Heiner, I., Glenner, H., Willerslev, E. & Kristensen, R.M. 2008. New data from an enigmatic phylum: evidence from molecular sequence data supports a sister-group relationship between Loricifera and Nematomorpha. Journal of zoological systematics and evolutionary research 46: 231–239. DOI: 10.1111/j.1439-0469.2008.00478.x

Vernacular names
Deutsch: Häutungstiere
English: Molting animals
français: Ecdysozoaires
magyar: Vedlő állatok
日本語: 脱皮動物 (だっぴどうぶつ)
한국어: 탈피동물
polski: Wylinkowce
português: Ecdisozoários
中文: 蛻皮動物

cdysozoa (/ˌɛkdɪsoʊˈzoʊə/) is a group of protostome animals,[3] including Arthropoda (insects, chelicerata, 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.[4] 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.[5]

A large study in 2008 by Dunn et al. strongly supported the monophyly of Ecdysozoa.[6]

The group Ecdysozoa is supported by many morphological characters, including growth by ecdysis with moulting of the cuticle without mitosis in the epirdermis under control of the prohormone ecdysone, and internal fertilization.[7]

The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques,[8] while others contested the interpretation of the molecular data.[9][10]

The name Ecdysozoa stems etymologically from Ancient Greek ἔκδυσις (ékdusis) 'shedding', and ζῷον (zôion) 'animal'.
See also: List of bilaterial animal orders

The most notable characteristic shared by ecdysozoans is a three-layered cuticle (four in Tardigrada[11]) 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.[12] 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.

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.[13] 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.[6] 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.[14]

A modern consensus phylogenetic tree for the protostomes is shown below.[15][16][17][18][19][20] It is indicated when approximately clades radiated into newer clades in millions of years ago (Mya); dashed lines show especially uncertain placements.[21]

The phylogenetic tree is based on Nielsen[22] with provisional placement of Loricifera from Hiroshi et al.[19]


Xenacoelomorpha Proporus sp.png


Priapulida Priapulus caudatus 20150625.jpg

Kinorhyncha Pycnophyes zelinkaei.jpg


Nematoda CelegansGoldsteinLabUNC.jpg

Nematomorpha Paragordius tricuspidatus.jpeg

Loricifera Pliciloricus enigmatus.jpg


Onychophora Velvet worm.jpg


Tardigrada Echiniscus L.png

Arthropoda Long nosed weevil edit.jpg

Spiralia Grapevinesnail 01.jpg Polychaeta (no).JPG

Kimberella †

Deuterostomia Common carp (white background).jpg Portugal 20140812-DSC01434 (21371237591).jpg

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,[23] though later considered them unrelated.[24] Inclusion of the roundworms within the Ecdysozoa was initially contested[9][25] but since 2003, a broad consensus has formed supporting the Ecdysozoa [26] 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.[27]
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.[28] 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.[29]

Howard, R. J., Giacomelli, M., Lozano-Fernandez, J., Edgecombe, G. D., Fleming, J. F., Kristensen, R. M., Ma, X., Olesen, J., Sørensen, M. V., Thomsen, P. F., Wills, M. A., Donoghue, P. C., & Pisani, D. (2022). The Ediacaran origin of ecdysozoa: Integrating fossil and Phylogenomic Data. Journal of the Geological Society, 179 (4).
Liu, Yunhuan; Carlisle, Emily; Zhang, Huaqiao; Yang, Ben; Steiner, Michael; Shao, Tiequan; Duan, Baichuan; Marone, Federica; Xiao, Shuhai (2022-08-17). "Saccorhytus is an early ecdysozoan and not the earliest deuterostome". Nature. 609 (7927): 541–546. doi:10.1038/s41586-022-05107-z. ISSN 1476-4687. PMID 35978194. S2CID 251646316.
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Eernisse, D. J.; Albert, J. S.; Anderson, F. E. (1992). "Annelida and Arthropoda are not sister taxa: a phylogenetic analysis of spiralian metazoan morphology". Systematic Biology. 41: 305–330.
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