Ambulacraria Explained

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 clade that also includes the many Chordata, and the few extinct species belonging to the Vetulicolia.

Phylogeny

The two living clades with representative organisms are:

(These together sometimes are called the lower deuterostomes.)

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] and other authors asserting that the best choices of phylogenetic methods support the position of Xenacoelomorpha as the sister group to Ambulacraria.[6] [7]

Two extinct taxa of uncertain placement, Vetulocystida and Yanjiahella, have each been proposed as either stem-group echinoderms[8] [9] or stem-group ambulacrarians.[10] [11] Vetulocystids have also been tentatively proposed as the basal-most stem-group chordates,[12] while Yanjiahella has also been proposed to be a stem-group hemichordate.

The following cladogram is based on a simplification of Li et al. 2023,[13] with the possible placements of uncertain potential ambulacrarians shown with dashed lines and question marks:

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.[14] [15] 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.[16]

Notes and References

  1. Cannon . Johanna Taylor. Vellutini . Bruno Cossermelli. Smith . Julian. Ronquist . Fredrik. Jondelius . Ulf. Hejnol . Andreas. Xenacoelomorpha is the sister group to Nephrozoa. Nature. 2016. 530 . 7588 . 89–93. 10.1038/nature16520. 26842059. 2016Natur.530...89C. 205247296.
  2. Web site: GenomeWeb. Sea Cucumber Genome Imparts Insight on Genes Linked to Organ Regeneration. 12 October 2017. 25 November 2024.
  3. Mitchell . C. E.. Melchin . M. J.. Cameron . C. B.. Maletz . J.. Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite. Lethaia. 2013. 46 . 1 . 34–56. 10.1111/j.1502-3931.2012.00319.x.
  4. 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. 11 . 2. 151–172. Organisms, Diversity & Evolution. 32169826.
  5. Greg W. . Rouse. Nerida G. . Wilson. Jose I. . Carvajal. Robert C. . Vriejenhoek. 10.1038/nature16545. New deep-sea species of Xenoturbella and the position of Xenacoelomorpha. 4 February 2016. 530 . 2. 94–97. Nature. 26842060. 2016Natur.530...94R. 3870574.
  6. Herve Philippe. etal. Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria. Current Biology. 10.1016/j.cub.2019.04.009. 3 June 2019. 29 . 11 . 1818–1826. 31104936. free. 21.11116/0000-0004-DC4B-1. free.
  7. Kapli . Paschalia. Telford . Maximilian J.. Topology-dependent asymmetry in systematic errors affects phylogenetic placement of Ctenophora and Xenacoelomorpha. Science Advances. 10.1126/sciadv.abc5162. 6 . 50 . eabc5162. 11 December 2020. 33310849. 7732190. 2020SciA....6.5162K. free.
  8. Shu . D.-G.. Conway Morris . S.. Han . J.. Zhang . Z.-F.. Liu . J.-N.. Ancestral echinoderms from the Chengjiang deposits of China. 2004. Nature. 430 . 6998 . 422–428. 10.1038/nature02648. 15269760. 2004Natur.430..422S. 4421182.
  9. Topper . Timothy P.. Guo . Junfeng. Clausen . Sébastien. Skovsted . Christian B.. Zhang . Zhifei. 2019-03-25. A stem group echinoderm from the basal Cambrian of China and the origins of Ambulacraria . Nature Communications. en. 10. 1. 1366. 10.1038/s41467-019-09059-3. 2041-1723. 6433856. 30911013. 2019NatCo..10.1366T.
  10. Conway Morris. Simon. Halgedahl. Susan L.. Selden. Paul. Jarrard. Richard D.. Rare primitive deuterostomes from the Cambrian (Series 3) of Utah. Journal of Paleontology. 2015. 89. 4. 631–636. 10.1017/jpa.2015.40. 2015JPal...89..631C.
  11. Zamora . Samuel. Wright . David F.. Mooi . Rich. Lefebvre . Bertrand. Guensburg . Thomas E.. Gorzelak . Przemysław. David . Bruno. Sumrall . Colin D.. Cole . Selina R.. Hunter . Aaron W.. Sprinkle . James. 2020-03-09. Re-evaluating the phylogenetic position of the enigmatic early Cambrian deuterostome Yanjiahella. Nature Communications. en. 11 . 1 . 1286. 10.1038/s41467-020-14920-x. 2041-1723. 7063041. 32152310. 2020NatCo..11.1286Z.
  12. Mussini . G.. Smith . M. P.. Vinther . J.. Rahman . I. A.. Murdock . D. J. E.. Harper . D. A. T.. Dunn . F. S.. 2024. A new interpretation of Pikaia reveals the origins of the chordate body plan. Current Biology. 34 . 13 . 2980–2989.e2. 10.1016/j.cub.2024.05.026 . free. 38866005. 2024CBio...34.2980M.
  13. Li . Yujing. Dunn . Frances S.. Murdock . Duncan J.E.. Guo . Jin. Rahman . Imran A.. Cong . Peiyun. Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome. Current Biology. May 10, 2023. 33 . 12 . 2359–2366.e2. 10.1016/j.cub.2023.04.048 . free. 37167976. 258592223. 2023CBio...33E2359L.
  14. Web site: Tutorial. Lacalli. Thurston Castle. Marine Invertebrate larvae: A study in morphological diversity. University of Saskatchewan. 2020-01-13.
  15. 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 . 10.1111/j.1525-142X.2007.00189.x.
  16. Web site: Dipleurula . 2020-01-13 . 1999 . Lexikon der Biologie . Spektrum Akademischer Verlag. Heidelberg . de.

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