Ambulacraria

Ambulacrarians; Temporal range:
	Various sea stars and sea urchins among mussel shells in the rocky intertidal zone of Kachemak Bay, southern Alaska, United States
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
Superphylum:	Deuterostomia
Clade:	Ambulacraria; Metschnikoff, 1881
Phyla
	Echinodermata; Hemichordata;

Ambulacraria /ˌæmbjuːləˈkrɛəriə/, or Coelomopora /siːləˈmɒpərə/, is a clade of invertebrate phyla that includes echinoderms and hemichordates;^[1] a member of this group is called an ambulacrarian. Phylogenetic analysis suggests the echinoderms and hemichordates separated around 533 million years ago.^[2] The Ambulacraria are part of the deuterostomes, a clade that also includes the many Chordata, and the few extinct species belonging to the Vetulicolia.

The two living clades with representative organisms are:

Echinodermata (sea stars, sea urchins, brittle stars, sea cucumbers, feather stars, sea lilies, etc.)
Hemichordata (acorn worms, Pterobranchia, and possibly graptolites)

(These together sometimes are called the lower deuterostomes.^[3])

Whether the Xenacoelomorpha clade is the sister group to the Ambulacraria remains a contentious issue, with some authors arguing that the former should be placed more basally among metazoans,^[4]^[5]^[6] and other authors asserting that the best choices of phylogenetic methods support the position of Xenacoelomorpha as the sister group to Ambulacraria.^[7]^[8]

^ Cannon, Johanna Taylor; Vellutini, Bruno Cossermelli; Smith, Julian; Ronquist, Fredrik; Jondelius, Ulf; Hejnol, Andreas (2016). "Xenacoelomorpha is the sister group to Nephrozoa". Nature. 530 (7588): 89–93. Bibcode:2016Natur.530...89C. doi:10.1038/nature16520. PMID 26842059. S2CID 205247296.
^ Sea Cucumber Genome Imparts Insight on Genes Linked to Organ Regeneration
^ Cite error: The named reference Lacalli was invoked but never defined (see the help page).
^ Edgecombe, Gregory D.; Giribet, Gonzalo; Dunn, Casey W.; Hejnol, Andreas; Kristensen, Reinhardt M.; Neves, Ricardo C.; Rouse, Greg W.; Worsaae, Katrine; Sørensen, Martin V. (June 2011). "Higher-level metazoan relationships: recent progress and remaining questions". Organisms, Diversity & Evolution. 11 (2): 151–172. doi:10.1007/s13127-011-0044-4. S2CID 32169826.
^ Rouse, Greg W.; Wilson, Nerida G.; Carvajal, Jose I.; Vriejenhoek, Robert C. (4 February 2016). "New deep-sea species of Xenoturbella and the position of Xenacoelomorpha". Nature. 530 (2): 94–97. Bibcode:2016Natur.530...94R. doi:10.1038/nature16545. PMID 26842060. S2CID 3870574.
^ Cannon, Johanna Taylor; Vellutini, Bruno Cossermelli; Smith III, Julian; Ronquist, Frederik; Jondelius, Ulf; Hejnol, Andreas (4 February 2016). "Xenacoelomorpha is the sister group to Nephrozoa". Nature. 530 (2): 89–93. Bibcode:2016Natur.530...89C. doi:10.1038/nature16520. PMID 26842059. S2CID 205247296.
^ Herve Philippe; et al. (3 June 2019). "Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria". Current Biology. 29 (11): 1818–1826. doi:10.1016/j.cub.2019.04.009. hdl:21.11116/0000-0004-DC4B-1. PMID 31104936.
^ Paschalia Kapli; Maximilian J. Telford (11 December 2020). "Topology-dependent asymmetry in systematic errors affects phylogenetic placement of Ctenophora and Xenacoelomorpha". Science Advances. 6 (50): eabc5162. Bibcode:2020SciA....6.5162K. doi:10.1126/sciadv.abc5162. PMC 7732190. PMID 33310849.

[1] Cannon, Johanna Taylor; Vellutini, Bruno Cossermelli; Smith, Julian; Ronquist, Fredrik; Jondelius, Ulf; Hejnol, Andreas (2016). "Xenacoelomorpha is the sister group to Nephrozoa". Nature. 530 (7588): 89–93. Bibcode:2016Natur.530...89C. doi:10.1038/nature16520. PMID 26842059. S2CID 205247296.

[2] Sea Cucumber Genome Imparts Insight on Genes Linked to Organ Regeneration

[Lacalli-3] Cite error: The named reference Lacalli was invoked but never defined (see the help page).

[4] Edgecombe, Gregory D.; Giribet, Gonzalo; Dunn, Casey W.; Hejnol, Andreas; Kristensen, Reinhardt M.; Neves, Ricardo C.; Rouse, Greg W.; Worsaae, Katrine; Sørensen, Martin V. (June 2011). "Higher-level metazoan relationships: recent progress and remaining questions". Organisms, Diversity & Evolution. 11 (2): 151–172. doi:10.1007/s13127-011-0044-4. S2CID 32169826.

[5] Rouse, Greg W.; Wilson, Nerida G.; Carvajal, Jose I.; Vriejenhoek, Robert C. (4 February 2016). "New deep-sea species of Xenoturbella and the position of Xenacoelomorpha". Nature. 530 (2): 94–97. Bibcode:2016Natur.530...94R. doi:10.1038/nature16545. PMID 26842060. S2CID 3870574.

[6] Cannon, Johanna Taylor; Vellutini, Bruno Cossermelli; Smith III, Julian; Ronquist, Frederik; Jondelius, Ulf; Hejnol, Andreas (4 February 2016). "Xenacoelomorpha is the sister group to Nephrozoa". Nature. 530 (2): 89–93. Bibcode:2016Natur.530...89C. doi:10.1038/nature16520. PMID 26842059. S2CID 205247296.

[7] Herve Philippe; et al. (3 June 2019). "Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria". Current Biology. 29 (11): 1818–1826. doi:10.1016/j.cub.2019.04.009. hdl:21.11116/0000-0004-DC4B-1. PMID 31104936.

[8] Paschalia Kapli; Maximilian J. Telford (11 December 2020). "Topology-dependent asymmetry in systematic errors affects phylogenetic placement of Ctenophora and Xenacoelomorpha". Science Advances. 6 (50): eabc5162. Bibcode:2020SciA....6.5162K. doi:10.1126/sciadv.abc5162. PMC 7732190. PMID 33310849.

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