deuterostome

Initially, Deuterostomia included the phyla Brachiopoda,{{Cite journal |last1=Eernisse |first1=Douglas J. |last2=Albert |first2=James S. |last3=Anderson |first3=Frank E. |date=1992-09-01 |title=Annelida and Arthropoda are Not Sister Taxa: A Phylogenetic Analysis of Spiralian Metazoan Morphology |url=https://academic.oup.com/sysbio/article/41/3/305/1676076 |journal=Systematic Biology |volume=41 |issue=3 |pages=305–330 |doi=10.1093/sysbio/41.3.305}} Bryozoa,{{cite journal |last=Nielsen |first=C. |date=July 2002 |title=The Phylogenetic Position of Entoprocta, Ectoprocta, Phoronida, and Brachiopoda |journal=Integrative and Comparative Biology |volume=42 |issue=3 |pages=685–691 |doi=10.1093/icb/42.3.685 |pmid=21708765 |doi-access=free }} Chaetognatha,{{cite book |last1=Brusca |first1=R.C. |last2=Brusca |first2=G.J. |year=1990 |title=Invertebrates |url=https://archive.org/details/invertebrates0000brus |url-access=registration |publisher=Sinauer Associates |page=[https://archive.org/details/invertebrates0000brus/page/669 669]}} and Phoronida 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.{{cite journal |last1=Halanych |first1=K.M. |author2=Bacheller, J. |author3=Liva, S. |author4=Aguinaldo, A. A. |author5=Hillis, D.M. |author6=Lake, J.A. |date=17 March 1995 |title=18S rDNA evidence that the Lophophorates are Protostome Animals |journal=Science |volume=267 |pages=1641–1643 |bibcode=1995Sci...267.1641H |doi=10.1126/science.7886451 |pmid=7886451 |issue=5204|s2cid=12196991 }} The arrow worms may also be deuterostomes, but molecular studies have placed them in the protostomes more often.{{Cite journal |last1=Marlétaz |first1=Ferdinand |last2=Martin |first2=Elise |last3=Perez |first3=Yvan |last4=Papillon |first4=Daniel |last5=Caubit |first5=Xavier |last6=Lowe |first6=Christopher J. |last7=Freeman |first7=Bob |last8=Fasano |first8=Laurent |last9=Dossat |first9=Carole |last10=Wincker |first10=Patrick |last11=Weissenbach |first11=Jean |display-authors=5 |date=2006-08-01 |title=Chaetognath phylogenomics: a protostome with deuterostome-like development |journal=Current Biology |volume=16 |issue=15 |pages=R577–R578 |doi=10.1016/j.cub.2006.07.016 |pmid=16890510 |s2cid=18339954 |doi-access=free |bibcode=2006CBio...16.R577M }}{{Cite journal |last1=Marlétaz |first1=Ferdinand |last2=Peijnenburg |first2=Katja T.C.A. |last3=Goto |first3=Taichiro |last4=Satoh |first4=Noriyuki |last5=Rokhsar |first5=Daniel S. |date=2019-01-21 |title=A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans |journal=Current Biology |volume=29 |issue=2 |pages=312–318.e3 |doi=10.1016/j.cub.2018.11.042 |pmid=30639106 |doi-access=free |bibcode=2019CBio...29E.312M }} 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.[https://news.berkeley.edu/2015/11/19/acorn-worm-genome-reveals-gill-origins-of-human-pharynx/ Acorn worm genome reveals gill origins of human pharynx |Berkeley News]

{{See also|List of bilateral animal orders}}

A consensus phylogeny of the deuterostomes is:{{cn|date=December 2024}}

• Superphylum Deuterostomia
• Phylum Chordata
• Subphylum Cephalochordata (lancelets)
• Clade Olfactores
• Subphylum Tunicata (tunicates)
• Subphylum Vertebrata
• Superclass Agnatha (jawless fish)
• Infraphylum Gnathostomata (jawed fish)
• Class Chondrichthyes (cartilaginous fish)
• Superclass Osteichthyes (bony fish - includes tetrapods)
• Clade Ambulacraria
• Phylum Hemichordata
• Class Enteropneusta (acorn worms)
• Class Planctosphaeroidea{{efn|Often considered part of Enteropneusta}}
• Class Pterobranchia
• Phylum Echinodermata
• Subphylum Asterozoa
• Class Asteroidea (starfish)
• Class Ophiuroidea (brittle stars)
• Subphylum Blastozoa †
• Subphylum Crinozoa (sea lillies and extinct relatives)
• Subphylum Echinozoa
• Echinoidea (sea urchins)
• Holothuroidea (sea cucumbers)

There is a possibility that Ambulacraria is the sister clade to Xenacoelomorpha, and could form the Xenambulacraria group.{{cite journal |last1=Bourlat |first1=Sarah J. |last2=Juliusdottir |first2=Thorhildur |last3=Lowe |first3=Christopher J. |last4=Freeman |first4=Robert |last5=Aronowicz |first5=Jochanan |last6=Kirschner |first6=Mark |last7=Lander |first7=Eric S. |last8=Thorndyke |first8=Michael |last9=Nakano |first9=Hiroaki |last10=Kohn |first10=Andrea B. |last11=Heyland |first11=Andreas |last12=Moroz |first12=Leonid L. |last13=Copley |first13=Richard R. |last14=Telford |first14=Maximilian J. |display-authors=5 |title=Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida |journal=Nature |volume=444 |issue=7115 |year=2006 |pages=85–88 |doi=10.1038/nature05241 |pmid=17051155 |bibcode=2006Natur.444...85B|s2cid=4366885 }}{{cite journal |last1=Philippe |first1=Hervé |last2=Poustka |first2=Albert J. |last3=Chiodin |first3=Marta |last4=Hoff |first4=Katharina J. |last5=Dessimoz |first5=Christophe |last6=Tomiczek |first6=Bartlomiej |last7=Schiffer |first7=Philipp H. |last8=Müller |first8=Steven |last9=Domman |first9=Daryl |last10=Horn |first10=Matthias |last11=Kuhl |first11=Heiner |last12=Timmermann |first12=Bernd |last13=Satoh |first13=Noriyuki |last14=Hikosaka-Katayama |first14=Tomoe |last15=Nakano |first15=Hiroaki |last16=Rowe |first16=Matthew L. |last17=Elphick |first17=Maurice R. |last18=Thomas-Chollier |first18=Morgane |last19=Hankeln |first19=Thomas |last20=Mertes |first20=Florian |last21=Wallberg |first21=Andreas |last22=Rast |first22=Jonathan P. |last23=Copley |first23=Richard R. |last24=Martinez |first24=Pedro |last25=Telford |first25=Maximilian J. |display-authors=5 |title=Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria |journal=Current Biology |volume=29 |issue=11 |year=2019 |pages=1818–1826.e6 |doi=10.1016/j.cub.2019.04.009 |pmid=31104936 |bibcode=2019CBio...29E1818P |hdl=21.11116/0000-0004-DC4B-1 |s2cid=155104811 |hdl-access=free }}{{cite journal |last=Marlétaz |first=Ferdinand |date=2019-06-17 |title=Zoology: Worming into the Origin of Bilaterians |journal=Current Biology |volume=29 |issue=12 |pages=R577–R579 |doi=10.1016/j.cub.2019.05.006 |pmid=31211978 |doi-access=free |bibcode=2019CBio...29.R577M }}

{{refimprove section|date=December 2024}}

File:Protovsdeuterostomes.svg

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.{{cite book |last1=Hejnol |first1=A. |last2=Martindale |first2=M. Q. |chapter=The mouth, the anus, and the blastopore - open questions about questionable openings |chapter-url=https://www.researchgate.net/publication/230766195 |title=Animal Evolution — Genomes, Fossils, and Trees |editor1=M. J. Telford |editor2=D. T. J. Littlewood |pages=33–40}}

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).{{cite journal |last1=Graham |first1=A. |last2=Richardson |first2=J. |title=Developmental and evolutionary origins of the pharyngeal apparatus |pmc=3564725 |pmid=23020903 |doi=10.1186/2041-9139-3-24 |volume=3 |issue=1 |year=2012 |journal=Evodevo |page=24 |doi-access=free }}{{cite book |last=Valentine |first=James W. |title=On the Origin of Phyla |date=June 18, 2004 |publisher=University of Chicago Press |isbn=978-0-226-84548-7 |url=https://books.google.com/books?id=DMBkmHm5fe4C&q=pharyngotremy%E2%80%94+the+presence+of+spiracles+or+gill+slits&pg=PA382 |page=382}}

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|date=September 2021}}

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.{{cite journal |author=Smith, Andrew B. |title=Cambrian problematica and the diversification of deuterostomes |journal=BMC Biology |pages=79 |date=2012 |doi=10.1186/1741-7007-10-79 |pmid=23031503 |pmc=3462677 |volume=10 |issue=79 |doi-access=free }}

File:EarlyDeuterostomeNT ordered.jpg

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.{{cite journal |last1=Erwin |first1=Douglas H. |last2=Davidson |first2=Eric H. |date=1 July 2002 |title=The last common bilaterian ancestor|journal=Development|volume=129|pages=3021–3032|url=http://dev.biologists.org/cgi/content/full/129/13/3021 |pmid=12070079 |issue=13 |doi=10.1242/dev.129.13.3021 }} It seems likely that the {{ma|555|million year old}} Kimberella was a member of the protostomes.{{The Rise and Fall of the Ediacaran Biota |last=Fedonkin |first=M.A. |author2=Simonetta, A |author3=Ivantsov, A.Y. |chapter=New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications |pages=157–179 |doi=10.1144/SP286.12}}{{cite journal |last=Butterfield |first=N.J. |date= December 2006 |title= Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale |journal= BioEssays |volume=28 |issue=12 |pages=1161–1166 |doi= 10.1002/bies.20507 |pmid= 17120226 |s2cid= 29130876 }} That implies that the protostome and deuterostome lineages split long before Kimberella appeared, and hence well before the start of the Cambrian {{ma|Cambrian}}, 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.{{cite journal |last1=Li |first1=Yujing |last2=Dunn |first2=Frances S. |last3=Murdock |first3=Duncan J.E. |last4=Guo |first4=Jin |last5=Rahman |first5=Imran A. |last6=Cong |first6=Peiyun |title=Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome |journal=Current Biology |date=May 10, 2023 |volume=33 |issue=12 |pages=2359–2366.e2 |doi=10.1016/j.cub.2023.04.048 |pmid=37167976 |doi-access=free |bibcode=2023CBio...33E2359L }}

The last common ancestor of the deuterostomes had lost all innexin diversity.[https://elifesciences.org/articles/74422 Connexins evolved after early chordates lost innexin diversity]

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{{cite journal |last1=Hahn |first1=G |last2=Pflug |first2=H. D |title=Polypenartige Organismen aus dem Jung-Präkambrium (Nama-Gruppe) von Namibia |journal=Pascal-Francis |date=1985 |issue=19 |pages=1–13 |url=http://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=8373330 |access-date=13 March 2024}} or sponges,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. 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.{{Cite journal |last1=Cracknell |first1=Kelsie |last2=García-Bellido |first2=Diego C. |last3=Gehling |first3=James G. |last4=Ankor |first4=Martin J. |last5=Darroch |first5=Simon A. F. |last6=Rahman |first6=Imran A. |date=2021-02-18 |title=Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities |journal=Scientific Reports |volume=11 |issue=1 |pages=4121 |doi=10.1038/s41598-021-83452-1 |pmc=7893023 |pmid=33602958|bibcode=2021NatSR..11.4121C }}{{Cite journal |last1=Zamora |first1=Samuel |last2=Wright |first2=David F. |last3=Mooi |first3=Rich |last4=Lefebvre |first4=Bertrand |last5=Guensburg |first5=Thomas E. |last6=Gorzelak |first6=Przemysław |last7=David |first7=Bruno |last8=Sumrall |first8=Colin D. |last9=Cole |first9=Selina R. |last10=Hunter |first10=Aaron W. |last11=Sprinkle |first11=James |last12=Thompson |first12=Jeffrey R. |last13=Ewin |first13=Timothy A. M. |last14=Fatka |first14=Oldřich |last15=Nardin |first15=Elise |display-authors=5 |date=2020-03-09 |title=Re-evaluating the phylogenetic position of the enigmatic early Cambrian deuterostome Yanjiahella |journal=Nature Communications |language=en |volume=11 |issue=1 |page=1286 |doi=10.1038/s41467-020-14920-x |pmc=7063041 |pmid=32152310 |bibcode=2020NatCo..11.1286Z }}

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, {{ma|521}}{{cite journal |author= Bengtson, S. |editor1= Lipps, J.H. |editor2= Waggoner, B.M. |title= Early Skeletal Fossils in Neoproterozoic–Cambrian Biological Revolutions |year= 2004 |journal= Paleontological Society Papers |volume= 10 |pages= 67–78 |url= http://www.nrm.se/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf |doi= 10.1017/S1089332600002345 |access-date= 2015-09-01 |archive-date= 2008-10-03 |archive-url= https://web.archive.org/web/20081003122817/http://www.nrm.se/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf |url-status= dead }} 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 body fossils of fish,{{cite journal |last1=Shu |first1=D.-G. |author2=Conway Morris, S. |author2-link=Simon Conway Morris |author3=Han, J. |title=Head and backbone of the Early Cambrian vertebrate Haikouichthys |journal=Nature |volume=421 |issue=6922 |pages=526–529 |date=January 2003 |pmid=12556891 |doi=10.1038/nature01264 |bibcode=2003Natur.421..526S |s2cid=4401274 |display-authors=etal}}{{cite journal |last1=Shu |first1=D.-G. |author2=Conway Morris, S. |author2-link=Simon Conway Morris |author3=Zhang, X.-L. |title=Lower Cambrian vertebrates from south China |journal=Nature |volume=402 |date=November 1999 |doi=10.1038/46965 |pages=42–46 |issue=6757 |bibcode=1999Natur.402...42S|s2cid=4402854 }} whereas Pikaia, discovered much earlier but from the Mid Cambrian Burgess Shale, is now regarded as a primitive chordate.{{cite journal |last1=Shu |first1=D.-G. |author2=Conway Morris, S. |author3=Zhang, X.-L. |title=A Pikaia-like chordate from the Lower Cambrian of China |journal=Nature |volume=384 |pages= 157–158 |date=November 1996 |doi=10.1038/384157a0 |issue=6605 |bibcode= 1996Natur.384..157S|s2cid=4234408 }} The Mid Cambrian fossil Rhabdotubus johanssoni has been interpreted as a pterobranch hemichordate,{{cite journal |last1=Bengtson |first1=S. |last2=Urbanek |first2=A. |date=October 2007 |title=Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate |journal=Lethaia |volume=19 |issue=4 |pages=293–308 |doi=10.1111/j.1502-3931.1986.tb00743.x }} 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|date=August 2024}}. Fossils of Echinodermata are very common after the Cambrian. Fossils of Hemichordata are less common, except for graptolites until the Lower Carbonoferous.

{{asof|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.{{cite journal |last=Swalla |first=Billie J |title=Deuterostome Ancestors and Chordate Origins |journal=Integrative and Comparative Biology |volume=64 |issue=5 |date=21 November 2024 |doi=10.1093/icb/icae134 |pages=1175–1181|pmid=39104213 }} Approximate dates for clades are given in millions of years ago (mya).{{cite journal |last1=Han |first1=Jian |last2=Morris |first2=Simon Conway |author2-link=Simon Conway Morris |last3=Ou |first3=Qian |last4=Shu|first4=Degan|last5=Huang|first5=Hai |title=Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China) |journal=Nature |date=2017 |volume=542|issue=7640 |pages=228–231 |doi=10.1038/nature21072|pmid=28135722 |bibcode=2017Natur.542..228H|s2cid=353780 }}

{{clade |style=font-size:85%;line-height:85%

|label1=Nephrozoa

|1={{clade

|label1=Deuterostomia

|1={{clade

|label1=Chordata

|1={{clade

|1=Cephalochordata 45 px

|label2=Olfactores

|2={{clade

|1=Tunicata 30 px

|2=Vertebrata 70px

|sublabel2=518 mya

}}

}}

|label2=Ambulacraria

|sublabel2=533 mya

|2={{clade

|1=Echinodermata 60 px

|label2=Hemichordata

|sublabel2=509 mya

|2={{clade

|1=Pterobranchia 50 px

|2=Enteropneusta 40 px

}}

}}

}}

|2=Protostomia 60 px

}}

}}

{{Notelist}}

{{Reflist}}

• {{cite journal|pmc=2615822 |year=2008 |last1=Swalla |first1=B. J. |last2=Smith |first2=A. B. |title=Deciphering deuterostome phylogeny: Molecular, morphological and palaeontological perspectives |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=363 |issue=1496 |pages=1557–1568 |doi=10.1098/rstb.2007.2246 |pmid=18192178 }}

{{Wikispecies|Deuterostomia}}

{{Commons category|Deuterostomia}}

• [http://www.ucmp.berkeley.edu/phyla/deuterostomia.html Introduction to the Deuterostomia] UCMP
• [https://www.britannica.com/animal/Deuterostomia Deuterostomia] at Encyclopædia Britannica

{{Animalia}}

{{Taxonbar|from=Q150866}}

Category:Bilaterians

Category:Ediacaran first appearances

Category:Superphyla

Category:Taxa named by Karl Grobben