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Deuterostome

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For the cell biology protein structure, see Deuterosome.

Deuterostomes (from Greek: lit. 'second mouth') are bilaterian animals of the superphylum Deuterostomia (/ˌdjuːtərəˈstoʊmi.ə/),[3][4] typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia is further divided into four phyla: Chordata, Echinodermata, Hemichordata, and the extinct Vetulicolia known from Cambrian fossils. The extinct clade Cambroernida is thought to be a member of Deuterostomia.

Deuterostomes
Temporal range: Earliest Cambrian–Present (Possible Ediacaran record, 557 Ma[1])
TunicateTetrapodActinopterygiiStarfishSea urchinCrinoidGraptoliteAcorn wormVetulicolia
Diversity of deuterostomes
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Grobben, 1908
Clades

In deuterostomes, the developing embryo's first opening (the blastopore) becomes the anus and cloaca, while the mouth is formed at a different site later on. This was initially the group's distinguishing characteristic, but deuterostomy has since been discovered among protostomes as well.[5] The deuterostomes are also known as enterocoelomates, because their coelom develops through pouching of the gut, enterocoely.

Deuterostomia's sister clade is Protostomia, animals that develop mouth first and whose digestive tract development is more varied. Protostomia includes the ecdysozoans and spiralians, as well as the extinct Kimberella.

Deuterostomia and Protostomia, together with their outgroup Xenacoelomorpha, constitute the large infrakingdom Bilateria, i.e. animals with bilateral symmetry and three germ layers.

Systematics

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History of classification

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Initially, Deuterostomia included the phyla Brachiopoda,[6] Bryozoa,[7] Chaetognatha,[8] and Phoronida[6] based on morphological and embryological characteristics. However, Deuterostomia was redefined in 1995 based on DNA molecular sequence analyses, leading to the removal of the lophophorates which was later combined with other protostome animals to form the superphylum Lophotrochozoa.[9] The arrow worms may also be deuterostomes,[8] but molecular studies have placed them in the protostomes more often.[10][11] Genetic studies have also revealed that deuterostomes have more than 30 genes not found in any other animal groups, but which yet are present in some marine algae and prokaryotes. This could mean that these are ancient genes that were lost in other organisms, or that a common ancestor acquired them through horizontal gene transfer.[12]

Taxonomy

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See also: List of bilateral animal orders

A consensus phylogeny of the deuterostomes is:[citation needed]

There is a possibility that Ambulacraria is the sister clade to Xenacoelomorpha, and could form the Xenambulacraria group.[13][14][15]

Characteristics

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Early development differences between deuterostomes versus protostomes. In deuterostomes, blastula divisions occur as radial cleavage because they occur parallel or perpendicular to the major polar axis. In protostomes, the cleavage is spiral because division planes are oriented obliquely to the polar major axis. During gastrulation, deuterostome embryos' anus is given first by the blastopore while the mouth is formed secondarily, and vice versa for the protostomes

In deuterostomes, the developing embryo's first opening, the blastopore, becomes the anus, while the gut eventually tunnels through the embryo until it reaches the other side, forming an opening that becomes the mouth. This distinguishes them from protostomes, which have a variety of patterns of development.[16]

In both deuterostomes and protostomes, a zygote first develops into a hollow ball of cells, called a blastula. In deuterostomes, the early divisions occur parallel or perpendicular to the polar axis. This is called radial cleavage, and also occurs in certain protostomes, such as the lophophorates.

Most deuterostomes display indeterminate cleavage, in which the developmental fate of the cells in the developing embryo is not determined by the identity of the parent cell. Thus, if the first four cells are separated, each can develop into a complete small larva; and if a cell is removed from the blastula, the other cells will compensate. This is the source of identical twins.

The mesoderm forms as evaginations of the developed gut that pinch off to form the coelom. This process is called enterocoely.

Another feature present in both the Hemichordata and Chordata is pharyngotremy — the presence of spiracles or gill slits into the pharynx, which is also found in some primitive fossil echinoderms (mitrates).[17][18]

A hollow nerve cord is found in all chordates, including tunicates (in the larval stage). Some hemichordates also have a tubular nerve cord. In the early embryonic stage, it looks like the hollow nerve cord of chordates.

Both the hemichordates and the chordates have a thickening of the aorta, homologous to the chordate heart, which contracts to pump blood. This suggests a presence in the deuterostome ancestor of the three groups, with the echinoderms having secondarily lost it.[citation needed]

The highly modified nervous system of echinoderms obscures much about their ancestry, but several facts suggest that all present deuterostomes evolved from a common ancestor that had pharyngeal gill slits, a hollow nerve cord, circular and longitudinal muscles and a segmented body.[19]

Origins and evolution

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Early deuterostomes and their modern counterparts

Bilateria, one of the five major lineages of animals, is split into two groups; the protostomes and deuterostomes. Deuterostomes consist of chordates (which include the vertebrates) and ambulacrarians.[20] It seems likely that the 555 million year old Kimberella was a member of the protostomes.[21][22] That implies that the protostome and deuterostome lineages split long before Kimberella appeared, and hence well before the start of the Cambrian 538.8 million years ago,[20] i.e. during the earlier part of the Ediacaran Period (circa 635-539 Mya, around the end of global Marinoan glaciation in the late Neoproterozoic). It has been proposed that the ancestral deuterostome, before the chordate/ambulacrarian split, could have been a chordate-like animal with a terminal anus and pharyngeal openings but no gill slits, with active suspension feeding strategy.[23]

The last common ancestor of the deuterostomes had lost all innexin diversity.[24]

Fossil record

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Deuterostomes have a rich fossil record with thousands of fossil species being found throughout the Phanerozoic. There are also a few earlier fossils that may represent deuterostomes, but these remain debated. The earliest of these disputed fossils are the tunicate-like organisms Burykhia and Ausia from the Ediacaran period. While these may in fact be tunicates, others have interpreted them as cnidarians[25] or sponges,[26] and as such their true affinity remains uncertain. Another Ediacaran fossil, Arkarua, may represent the earliest echinoderm, while Yanjiahella from the early Cambrian (Fortunian) period is another notable stem group echinoderm.[27][28]

Fossils of one major deuterostome group, the echinoderms (whose modern members include sea stars, sea urchins and crinoids), are quite common from the start of Stage 3 of the Cambrian, 521 million years ago[29] starting with forms such as Helicoplacus. Two other Cambrian Stage 3 (521-514 mya) species, Haikouichthys and Myllokunmingia from the Chengjiang biota, are the earliest bodyfossils of fish,[30][31] whereas Pikaia, discovered much earlier but from the Mid Cambrian Burgess Shale, is now regarded as a primitive chordate.[32] The Mid Cambrian fossil Rhabdotubus johanssoni has been interpreted as a pterobranch hemichordate,[33] whereas Spartobranchus is an acorn-worm from the Burgess Shale, providing proof that all main lineages were already well established 508 mya.

On the other hand, fossils of early chordates are very rare, as non-vertebrate chordates have no bone tissue or teeth, and fossils of no Post-Cambrian non-vertebrate chordates are known aside from the Permian-aged Paleobranchiostoma, trace fossils of the Ordovician colonial tunicate Catellocaula, and various Jurassic-aged and Tertiary-aged spicules tentatively attributed to ascidians.[citation needed]. Fossils of Echinodermata remain very common after the Cambrian. Fossils of Hemichordata are less common, except for graptolites until the Lower-Carbonoferous.

Phylogeny

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As of 2024, the deuterostomes are considered to be monophyletic. The ancestral deuterostome was most likely a benthic worm that possessed a cartilaginous skeleton, a central nervous system, and gill slits.[34] Approximate dates for clades are given in millions of years ago (mya).[35]

Nephrozoa

Notes

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  1. ^ Often considered part of Enteropneusta

References

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  1. ^ Fedonkin, M. A.; Vickers-Rich, P.; Swalla, B. J.; Trusler, P.; Hall, M. (2012). "A new metazoan from the Vendian of the White Sea, Russia, with possible affinities to the ascidians". Paleontological Journal. 46 (1): 1–11. Bibcode:2012PalJ...46....1F. doi:10.1134/S0031030112010042. S2CID 128415270.
  2. ^ Han, Jian; Morris, Simon Conway; Ou, Qiang; Shu, Degan; Huang, Hai (2017). "Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)". Nature. 542 (7640): 228–231. Bibcode:2017Natur.542..228H. doi:10.1038/nature21072. PMID 28135722. S2CID 353780.
  3. ^ Wade, Nicholas (30 January 2017). "This Prehistoric Human Ancestor Was All Mouth". The New York Times. Retrieved 31 January 2017.
  4. ^ Han, Jian; Morris, Simon Conway; Ou, Qiang; Shu, Degan; Huang, Hai (2017). "Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)". Nature. 542 (7640): 228–231. Bibcode:2017Natur.542..228H. doi:10.1038/nature21072. PMID 28135722. S2CID 353780.
  5. ^ Martín-Durán, José M.; Passamaneck, Yale J.; Martindale, Mark Q.; Hejnol, Andreas (2016). "The developmental basis for the recurrent evolution of deuterostomy and protostomy". Nature Ecology & Evolution. 1 (1): 0005. Bibcode:2016NatEE...1....5M. doi:10.1038/s41559-016-0005. PMID 28812551. S2CID 90795.
  6. ^ a b Eernisse, Douglas J.; Albert, James S.; Anderson, Frank E. (1992-09-01). "Annelida and Arthropoda are Not Sister Taxa: A Phylogenetic Analysis of Spiralian Metazoan Morphology". Systematic Biology. 41 (3): 305–330. doi:10.1093/sysbio/41.3.305.
  7. ^ Nielsen, C. (July 2002). "The Phylogenetic Position of Entoprocta, Ectoprocta, Phoronida, and Brachiopoda". Integrative and Comparative Biology. 42 (3): 685–691. doi:10.1093/icb/42.3.685. PMID 21708765.
  8. ^ a b Brusca, R.C.; Brusca, G.J. (1990). Invertebrates. Sinauer Associates. p. 669.
  9. ^ Halanych, K.M.; Bacheller, J.; Liva, S.; Aguinaldo, A. A.; Hillis, D.M.; Lake, J.A. (17 March 1995). "18S rDNA evidence that the Lophophorates are Protostome Animals". Science. 267 (5204): 1641–1643. Bibcode:1995Sci...267.1641H. doi:10.1126/science.7886451. PMID 7886451. S2CID 12196991.
  10. ^ Marlétaz, Ferdinand; Martin, Elise; Perez, Yvan; Papillon, Daniel; Caubit, Xavier; et al. (2006-08-01). "Chaetognath phylogenomics: a protostome with deuterostome-like development". Current Biology. 16 (15): R577–R578. Bibcode:2006CBio...16.R577M. doi:10.1016/j.cub.2006.07.016. PMID 16890510. S2CID 18339954.
  11. ^ Marlétaz, Ferdinand; Peijnenburg, Katja T.C.A.; Goto, Taichiro; Satoh, Noriyuki; Rokhsar, Daniel S. (2019-01-21). "A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans". Current Biology. 29 (2): 312–318.e3. Bibcode:2019CBio...29E.312M. doi:10.1016/j.cub.2018.11.042. PMID 30639106.
  12. ^ Acorn worm genome reveals gill origins of human pharynx |Berkeley News
  13. ^ Bourlat, Sarah J.; Juliusdottir, Thorhildur; Lowe, Christopher J.; Freeman, Robert; Aronowicz, Jochanan; et al. (2006). "Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida". Nature. 444 (7115): 85–88. Bibcode:2006Natur.444...85B. doi:10.1038/nature05241. PMID 17051155. S2CID 4366885.
  14. ^ Philippe, Hervé; Poustka, Albert J.; Chiodin, Marta; Hoff, Katharina J.; Dessimoz, Christophe; et al. (2019). "Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria". Current Biology. 29 (11): 1818–1826.e6. Bibcode:2019CBio...29E1818P. doi:10.1016/j.cub.2019.04.009. hdl:21.11116/0000-0004-DC4B-1. PMID 31104936. S2CID 155104811.
  15. ^ Marlétaz, Ferdinand (2019-06-17). "Zoology: Worming into the Origin of Bilaterians". Current Biology. 29 (12): R577–R579. Bibcode:2019CBio...29.R577M. doi:10.1016/j.cub.2019.05.006. PMID 31211978.
  16. ^ Hejnol, A.; Martindale, M. Q. "The mouth, the anus, and the blastopore - open questions about questionable openings". In M. J. Telford; D. T. J. Littlewood (eds.). Animal Evolution — Genomes, Fossils, and Trees. pp. 33–40.
  17. ^ Graham, A.; Richardson, J. (2012). "Developmental and evolutionary origins of the pharyngeal apparatus". Evodevo. 3 (1): 24. doi:10.1186/2041-9139-3-24. PMC 3564725. PMID 23020903.
  18. ^ Valentine, James W. (June 18, 2004). On the Origin of Phyla. University of Chicago Press. p. 382. ISBN 978-0-226-84548-7.
  19. ^ Smith, Andrew B. (2012). "Cambrian problematica and the diversification of deuterostomes". BMC Biology. 10 (79): 79. doi:10.1186/1741-7007-10-79. PMC 3462677. PMID 23031503.
  20. ^ a b Erwin, Douglas H.; Davidson, Eric H. (1 July 2002). "The last common bilaterian ancestor". Development. 129 (13): 3021–3032. doi:10.1242/dev.129.13.3021. PMID 12070079.
  21. ^ Fedonkin, M.A.; Simonetta, A; Ivantsov, A.Y. (2007), "New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications", in Vickers-Rich, Patricia; Komarower, Patricia (eds.), The Rise and Fall of the Ediacaran Biota, Special publications, vol. 286, London: Geological Society, pp. 157–179, doi:10.1144/SP286.12, ISBN 978-1-86239-233-5, OCLC 156823511
  22. ^ Butterfield, N.J. (December 2006). "Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale". BioEssays. 28 (12): 1161–1166. doi:10.1002/bies.20507. PMID 17120226. S2CID 29130876.
  23. ^ Li, Yujing; Dunn, Frances S.; Murdock, Duncan J.E.; Guo, Jin; Rahman, Imran A.; Cong, Peiyun (May 10, 2023). "Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome". Current Biology. 33 (12): 2359–2366.e2. Bibcode:2023CBio...33E2359L. doi:10.1016/j.cub.2023.04.048. PMID 37167976.
  24. ^ Connexins evolved after early chordates lost innexin diversity
  25. ^ Hahn, G; Pflug, H. D (1985). "Polypenartige Organismen aus dem Jung-Präkambrium (Nama-Gruppe) von Namibia". Pascal-Francis (19): 1–13. Retrieved 13 March 2024.
  26. ^ M. A. Fedonkin (1996). "Ausia as an ancestor of archeocyathans, and other sponge-like organisms". In: Enigmatic Organisms in Phylogeny and Evolution. Abstracts. Moscow, Paleontological Institute, Russian Academy of Sciences, p. 90-91.
  27. ^ Cracknell, Kelsie; García-Bellido, Diego C.; Gehling, James G.; Ankor, Martin J.; Darroch, Simon A. F.; Rahman, Imran A. (2021-02-18). "Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities". Scientific Reports. 11 (1): 4121. Bibcode:2021NatSR..11.4121C. doi:10.1038/s41598-021-83452-1. PMC 7893023. PMID 33602958.
  28. ^ Zamora, Samuel; Wright, David F.; Mooi, Rich; Lefebvre, Bertrand; Guensburg, Thomas E.; et al. (2020-03-09). "Re-evaluating the phylogenetic position of the enigmatic early Cambrian deuterostome Yanjiahella". Nature Communications. 11 (1): 1286. Bibcode:2020NatCo..11.1286Z. doi:10.1038/s41467-020-14920-x. PMC 7063041. PMID 32152310.
  29. ^ Bengtson, S. (2004). Lipps, J.H.; Waggoner, B.M. (eds.). "Early Skeletal Fossils in Neoproterozoic–Cambrian Biological Revolutions" (PDF). Paleontological Society Papers. 10: 67–78. doi:10.1017/S1089332600002345. Archived from the original (PDF) on 2008-10-03. Retrieved 2015-09-01.
  30. ^ Shu, D.-G.; Conway Morris, S.; Han, J.; et al. (January 2003). "Head and backbone of the Early Cambrian vertebrate Haikouichthys". Nature. 421 (6922): 526–529. Bibcode:2003Natur.421..526S. doi:10.1038/nature01264. PMID 12556891. S2CID 4401274.
  31. ^ Shu, D.-G.; Conway Morris, S.; Zhang, X.-L. (November 1999). "Lower Cambrian vertebrates from south China". Nature. 402 (6757): 42–46. Bibcode:1999Natur.402...42S. doi:10.1038/46965. S2CID 4402854.
  32. ^ Shu, D.-G.; Conway Morris, S. & Zhang, X.-L. (November 1996). "A Pikaia-like chordate from the Lower Cambrian of China". Nature. 384 (6605): 157–158. Bibcode:1996Natur.384..157S. doi:10.1038/384157a0. S2CID 4234408.
  33. ^ Bengtson, S.; Urbanek, A. (October 2007). "Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate". Lethaia. 19 (4): 293–308. doi:10.1111/j.1502-3931.1986.tb00743.x.
  34. ^ Swalla, Billie J (21 November 2024). "Deuterostome Ancestors and Chordate Origins". Integrative And Comparative Biology. 64 (5): 1175–1181. doi:10.1093/icb/icae134.
  35. ^ Han, Jian; Morris, Simon Conway; Ou, Qian; Shu, Degan; Huang, Hai (2017). "Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)". Nature. 542 (7640): 228–231. Bibcode:2017Natur.542..228H. doi:10.1038/nature21072. PMID 28135722. S2CID 353780.

Further reading

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