Ambulacraria

Ambulacraria, or Coelomopora, 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 larger clade that also includes the Chordata, Vetulicolia and Saccorhytus.

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

The two living clades with representative organisms are:

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

The group Xenoturbellida (two species of worm-like animals) had previously been considered to be in this clade but is now considered to be placed more basally among metazoans.[4]

Fossil taxa that may lie on the stem lineage:

Ontogeny

As for many animals, the egg cell of any extant ambulacrarian by cell division evolves to a blastula ("cell ball"), which evolves to a triploblast ("three-layered") gastrula. The gastrula then evolves to a dipleurula larva form, which is specific for the ambulacraria.[3] 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 larvae, whence this hypothetic ancestor sometimes also is called dipleurula.[7]

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gollark: Well, I mean, comparatively easy.
gollark: The limiting factor here is probably your key thing. There are only 4 billion possibilities for that, which is easy.
gollark: So effectively you just have a mildly larger key.

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.
  2. Sea Cucumber Genome Imparts Insight on Genes Linked to Organ Regeneration
  3. 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.
  5. 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.
  6. Murray, J.; MacGabhann, B. A. (2010). "Non-mineralised discoidal fossils from the Ordovician Bardahessiagh Formation, Co. Tyrone, Ireland". Irish Journal of Earth Sciences. 28: 1–12. doi:10.3318/IJES.2010.28.1.
  7. "Dipleurula". Lexikon der Biologie (in German). Spektrum Akademischer Verlag. Heidelberg. 1999. Retrieved 2020-01-13.
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