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 Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Clade: Ambulacraria
Metschnikoff, 1881
Phyla

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:

(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]

Fossil taxa that may lie on the stem lineage:

Ontogeny

As for many animals, the egg cell of any extant ambulacrarian divides and develops into a blastula ("cell ball"), which develops into a triploblast ("three-layered") gastrula. The gastrula then develops into a dipleurula larva form in the Asteroidea, Holothuroidea, Crinoidea, and Hemichordata, and into a pluteus larva form in the Echinoidea and Ophiuroidea.[3][10] This, in its turn, is developed in various different kinds of larvae for different taxa of ambulacrarians.

It has been suggested that the adult form of the last common ancestor of the ambulacrarians was anatomically similar to the dipleurula larva; this hypothetic ancestor sometimes also is called dipleurula.[11]

References

  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
  3. 1 2 Lacalli, Thurston Castle. "Tutorial". Marine Invertebrate larvae: A study in morphological diversity. University of Saskatchewan. Retrieved 2020-01-13.
  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.
  9. ↑ Caron, J.; Conway Morris, S.; Shu, D. (2010). "Tentaculate fossils from the Cambrian of Canada (British Columbia) and China (Yunnan) interpreted as primitive deuterostomes". PLOS ONE. 5 (3): e9586. Bibcode:2010PLoSO...5.9586C. doi:10.1371/journal.pone.0009586. PMC 2833208. PMID 20221405.
  10. ↑ Byrne, Maria; Nakajima, Yoko; Chee, Francis C.; Burke, Robert D. (2007). "Apical organs in echinoderm larvae: insights into larval evolution in the Ambulacraria". Evolution & Development. 9: 434–435, 438–440. doi:10.1111/j.1525-142X.2007.00189.x.
  11. ↑ "Dipleurula". Lexikon der Biologie (in German). Spektrum Akademischer Verlag. Heidelberg. 1999. Retrieved 2020-01-13.
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