Editing Tunicate (section)

== Taxonomy ==
[[File:Bluebell tunicates Nick Hobgood.jpg|thumb|right|''[[Clavelina moluccensis]]'', the bluebell tunicate]]
[[File:Botrylloides violaceus (cropped).jpg|thumb|right|''[[Botrylloides violaceus]]'' showing oral tentacles at openings of buccal siphons]]

About 3,000 species of tunicate exist in the world's oceans, living mostly in shallow water. The most numerous group is the [[ascidians]]; fewer than 100 species of these are found at depths greater than {{convert|200|m|abbr=on}}.<ref name=Ruppert/> Some are solitary animals leading a [[sessility (zoology)|sessile]] existence attached to the seabed, but others are [[Colony (biology)|colonial]] and a few are [[pelagic]]. Some are supported by a stalk, but most are attached directly to a [[Substrate (biology)|substrate]], which may be a rock, shell, coral, seaweed, [[mangrove]] root, dock, piling, or ship's hull. They are found in a range of solid or translucent colours and may resemble seeds, grapes, peaches, barrels, or bottles. One of the largest is a stalked sea tulip, ''[[Pyura pachydermatina]]'', which can grow to be over {{convert|1|m|ft}} tall.<ref name=Ruppert/>

The Tunicata were established by [[Jean-Baptiste Lamarck]] in 1816. In 1881, [[Francis Maitland Balfour]] introduced another name for the same group, "Urochorda", to emphasize the affinity of the group to other chordates.<ref>Foster, M. (ed.); Sedgwick, Adam (ed.); The Works of Francis Maitland Balfour. Vol. III. Memorial edition. Pub: Macmillan and co. 1885. May be downloaded from [https://archive.org/details/worksoffrancisma03balf]</ref> No doubt largely because of his influence, various authors supported the term, either as such, or as the slightly older "Urochordata", but this usage is invalid because "Tunicata" has precedence, and grounds for superseding the name never existed. Accordingly, the current (formally correct) trend is to abandon the name Urochorda or Urochordata in favour of the original Tunicata, and the name Tunicata is almost invariably used in modern scientific works. It is accepted as valid by the World Register of Marine Species<ref>[http://www.marinespecies.org/aphia.php?p=taxdetails&id=146420 Tunicata] World Register of Marine Species. Retrieved 2011-11-12.</ref> but not by the Integrated Taxonomic Information System.<ref>[https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=203347 Tunicata Lamarck, 1816] Integrated Taxonomic Information System. Retrieved 2017-03-30.</ref>

Various common names are used for different species. Sea tulips are tunicates with colourful bodies supported on slender stalks.<ref>{{cite web |url=https://australian.museum/learn/animals/sea-squirts/ |title=Sea squirts and sea tulips |publisher=Australian Museum |access-date=2013-09-25}}</ref> Sea squirts are so named because of their habit of contracting their bodies sharply and squirting out water when disturbed.<ref name="TwoCeans">{{cite web |url=http://dictionary.reference.com/browse/sea+squirt |title=Sea squirt |work=Dictionary.com |access-date=2013-09-25}}</ref> Sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat.<ref>{{cite web |url=http://www.sms.si.edu/irlfieldguide/Aplidi_stella.htm |title=Sea pork, ''Aplidium stellatum'' |publisher=Smithsonian at Fort Pierce |access-date=2013-09-25}}</ref>

=== Classification ===
Tunicates are more closely related to [[craniate]]s (including [[hagfish]], [[lamprey]]s, and jawed [[vertebrate]]s) than to [[lancelet]]s, [[echinoderm]]s, [[hemichordate]]s, ''[[Xenoturbella]]'' or other [[invertebrate]]s.<ref name="pmid16495997">{{cite journal |author1=Delsuc, F. |author2=Brinkmann, H. |author3=Chourrout, D. |author4=Philippe, H. |title=Tunicates and not cephalochordates are the closest living relatives of vertebrates |journal=Nature |volume=439 |issue=7079 |pages=965–968 |year=2006 |pmid=16495997 |doi=10.1038/nature04336 |bibcode=2006Natur.439..965D |s2cid=4382758 |url=http://hal-sde.archives-ouvertes.fr/docs/00/31/54/36/PDF/Delsuc-Nature06_HAL.pdf }}</ref><ref name="pmid19003928">{{cite journal |author1=Delsuc, F. |author2=Tsagkogeorga, G. |author3=Lartillot, N. |author4=Philippe, H. |title=Additional molecular support for the new chordate phylogeny |journal=Genesis |volume=46 |issue=11 |pages=592–604 | year=2008 |pmid=19003928 |doi=10.1002/dvg.20450 |s2cid=205771088 |url=https://hal.archives-ouvertes.fr/halsde-00338411 |doi-access=free }}</ref><ref name="pmid19922605">{{cite journal |author1=Singh, T. R. |author2=Tsagkogeorga, G. |author3=Delsuc, F. |author4=Blanquart, S. |author5=Shenkar, N. |author6=Loya, Y. |author7=Douzery, E. J. |author8=Huchon, D. |title=Tunicate mitogenomics and phylogenetics: peculiarities of the ''Herdmania momus'' mitochondrial genome and support for the new chordate phylogeny |journal=BMC Genomics |volume=10 |page=534 |year=2009 |pmid=19922605 |doi=10.1186/1471-2164-10-534 |pmc=2785839 |doi-access=free }}</ref>

The [[clade]] consisting of tunicates and vertebrates is called [[Olfactores]].<ref>Jefferies, R. P. S. (1991) in Biological Asymmetry and Handedness (eds Bock, G. R.; Marsh, J.) pp. 94–127 (Wiley, Chichester).</ref>

The Tunicata contain roughly 3,051 described species,<ref name=Ruppert/> traditionally divided into these classes:
* [[Ascidiacea]] ([[Aplousobranchia]], [[Phlebobranchia]], and [[Stolidobranchia]])
* [[Thaliacea]] ([[Pyrosome|Pyrosomida]], [[Doliolida]], and [[Salp]]ida)
* [[Larvacean|Appendicularia]] ([[Copelata]])

Members of the [[Sorberacea]] were included in Ascidiacea in 2011 as a result of [[ribosomal DNA|rDNA]] sequencing studies.<ref name="Tatian">{{cite journal |author1=Tatián, Marcos |author2=Lagger, Cristian |author3=Demarchi, Milagros |author4=Mattoni, Camilo |year=2011 |title=Molecular phylogeny endorses the relationship between carnivorous and filter-feeding tunicates (Tunicata, Ascidiacea) |journal=Zoologica Scripta |volume=40 |issue=6 |pages=603–612 |doi=10.1111/j.1463-6409.2011.00493.x |s2cid=86421513 }}</ref> Although the traditional classification is provisionally accepted, newer evidence suggests the Ascidiacea are an artificial group of [[paraphyletic]] status.<ref name="Zeng2005">{{cite journal |author1=Zeng, L. |author2=Swalla, B. J. |title=Molecular phylogeny of the protochordates: chordate evolution |journal=Can. J. Zool. |volume=83 |pages=24–33 |year=2005 |doi=10.1139/z05-010 }}</ref><ref name="pmid19656395">{{cite journal |author1=Tsagkogeorga, G. |author2=Turon, X. |author3=Hopcroft, R. R. |author4=Tilak, M. K. |author5=Feldstein, T. |author6=Shenkar, N. |author7=Loya, Y. |author8=Huchon, D. |author9=Douzery, E. J. |author10=Delsuc, F. |title=An updated 18S rRNA phylogeny of tunicates based on mixture and secondary structure models|journal=BMC Evolutionary Biology |volume=9 |page=187 |year=2009 |issue=1 |pmid=19656395 |doi=10.1186/1471-2148-9-187 |pmc=2739199 |bibcode=2009BMCEE...9..187T |doi-access=free }}</ref><ref name=Delsuc2018>{{cite journal |vauthors=Delsuc F, Philippe H, Tsagkogeorga G, Simion P, Tilak MK, Turon X, López-Legentil S, Piette J, Lemaire P, Douzery EJ |date=April 2018 |title=A phylogenomic framework and timescale for comparative studies of tunicates |journal=BMC Biology |volume=16 |issue=1 |page=39 |doi=10.1186/s12915-018-0499-2 |pmc=5899321 |pmid=29653534 |doi-access=free }}</ref> A close relationship between Thaliacea and Ascidiacea, with the former possibly emerging from the latter, had already been proposed since the early 20th century under the name of Acopa.<ref>{{cite journal |url=https://core.ac.uk/download/pdf/39301635.pdf |title=Phylogenetic Speculation of the Tunicata |last1=Tokioka |first1=Takasi |date=1971-06-30 |journal=Publications of the Seto Marine Biological Laboratory |volume=19 |issue=1 |page=47 |doi=10.5134/175655 |s2cid=55491438 }}</ref>

The following cladogram is based on the 2018 phylogenomic study of Delsuc and colleagues.<ref>{{Cite journal |last1=Franchi |first1=Nicola |last2=Ballarin |first2=Loriano |year=2017 |title=Immunity in Protochordates: The Tunicate Perspective |journal=Frontiers in Immunology |volume=8 |page=674 |doi=10.3389/fimmu.2017.00674 |pmc=5465252 |pmid=28649250 |doi-access=free}}</ref><ref name=Delsuc2018/><ref>{{Cite journal |last=Giribet |first=Gonzalo |year=2018 |title=Phylogenomics resolves the evolutionary chronicle of our squirting closest relatives |journal=BMC Biology |volume=16 |issue=1 |page=49 |doi=10.1186/s12915-018-0517-4 |pmc=5924484 |pmid=29703197 |doi-access=free}}</ref>

{{clade
|label1='''Tunicata'''
|1={{clade
   |label1=[[Larvacean|Appendicularia]]
   |1={{clade
      |1=[[Oikopleuridae]] [[File:Oikopleura_dioica.gif|40 px]]
      |2={{clade
         |1=[[Kowalevskiidae]] 
         |2=[[Fritillariidae]] [[File:Appendicularia_%28YPM_IZ_096169%29.jpeg|60 px]] }} }}
   |label2=Acopa
   |2={{clade
      |1={{clade
         |label1=[[Thaliacea]]
         |1={{clade
            |1=[[Pyrosomida]] [[File:Pyrosoma_atlanticum.JPG|60 px]]
            |2=[[Salpida]] [[File:Salp_colony,_Aorangaia_PA171899.JPG|60 px]]
            |3=[[Doliolida]] [[File: Cyclomyaria.jpg|60 px]]
            }}
         |label2=Enterogona
         |2={{clade
            |1=[[Phlebobranchia]] [[File: CionaintestinalisR.jpg|60 px]] |bar1=green
            |2=[[Aplousobranchia]]&nbsp;  [[File: Sea_Squirts_Didemnum_molle.jpg|60 px]] |bar2=green
            }}
         }}
      |grouplabel2=[[Ascidiacea]] |grouplabelstyle2=vertical-align:top;|bar2=green
      |2={{clade 
         |label1=[[Stolidobranchia]] 
         |1={{clade
            |1=[[Molgulidae]] [[File: Molgula_oculata_001.png|60 px]]
            |2={{clade
               |1=[[Styelidae]] [[File:Tunicate_komodo.jpg|60 px]]
               |2=[[Pyuridae]] [[File:Microcosmus_sabatieri.jpg|60 px]]
               }}
            }}
         }}
      }}
  }}
|style=font-size:100%;line-height:100%}}

===Fossil record===
[[Image:Catellocaula.jpg|thumb|right|The star-shaped holes (''[[Catellocaula vallata]]'') in this Upper Ordovician bryozoan may represent a tunicate preserved by [[Fossil#Bioimmuration|bioimmuration]] in the [[bryozoa]]n skeleton.]]
Undisputed fossils of tunicates are rare. The best known and earliest unequivocally identified species is ''[[Shankouclava|Shankouclava shankouense]]'' from the Lower [[Cambrian]] [[Maotianshan Shale]] at Shankou village, Anning, near [[Kunming]] ([[Northern and southern China|South China]]).<ref name=Jun-Yuan2003>{{cite journal|author1=Chen, Jun-Yuan |author2=Huang, Di-Ying |author3=Peng, Qing-Qing |author4=Chi, Hui-Mei |author5=Wang,Xiu-Qiang |author6=Feng, Man |year=2003 |title=The first tunicate from the Early Cambrian of South China |journal=[[Proceedings of the National Academy of Sciences]] |volume=100 |pmid=12835415 |issue=14 |pages=8314–8318 |pmc=166226 |doi=10.1073/pnas.1431177100 |bibcode=2003PNAS..100.8314C |doi-access=free }}</ref> There is also a common [[Fossil#Bioimmuration|bioimmuration]], (''Catellocaula vallata''), of a possible tunicate found in Upper [[Ordovician]] [[bryozoa]]n skeletons of the upper midwestern United States.<ref>{{cite journal |author1=Palmer, T. J. |author2=Wilson, M. A. |year=1988 |title=Parasitism of Ordovician bryozoans and the origin of pseudoborings |journal=Palaeontology |volume=31 |pages=939–949 |url=http://palaeontology.palass-pubs.org/pdf/Vol%2031/Pages%20939-949.pdf |access-date=7 April 2013 |archive-url=https://web.archive.org/web/20130927070328/http://palaeontology.palass-pubs.org/pdf/Vol%2031/Pages%20939-949.pdf |archive-date=27 September 2013 |url-status=usurped }}</ref> A well-preserved Cambrian fossil, ''Megasiphon thylakos'', shows that the tunicate basic body design had already been established 500 million years ago.<ref>{{Cite web |url=https://www.techexplorist.com/500-million-year-old-fossil-reveals-amazing-secrets-tunicate-origins/63818/ |title=A 500 million-year-old fossil reveals the amazing secrets of tunicate origins |first=Vidya |last=Nagalwade |date=7 July 2023 |website=Tech Explorist}}</ref>

Three enigmatic species were also found from the [[Ediacaran]] period – ''[[Ausia (animal)|Ausia fenestrata]]'' from the Nama Group of [[Namibia]], the sac-like ''[[Yarnemia|Yarnemia ascidiformis]]'', and one from a second new ''Ausia''-like genus from the Onega Peninsula of northern [[Russia]], ''[[Burykhia|Burykhia hunti]]''. Results of a new study have shown possible affinity of these Ediacaran organisms to the ascidians.<ref name=Vickers-Rich>Vickers-Rich P. (2007). "Chapter 4. The Nama Fauna of Southern Africa". In: Fedonkin, M. A.; Gehling, J. G.; Grey, K.; Narbonne, G. M.; Vickers-Rich, P. "The Rise of Animals: Evolution and Diversification of the Kingdom Animalia", Johns Hopkins University Press. pp. 69–87</ref><ref name=Oslo_2008>Fedonkin, M. A.; Vickers-Rich, P.; Swalla, B.; Trusler, P.; Hall, M. (2008). "A Neoproterozoic chordate with possible affinity to the ascidians: New fossil evidence from the Vendian of the White Sea, Russia and its evolutionary and ecological implications". HPF-07 Rise and fall of the Ediacaran (Vendian) biota. International Geological Congress - Oslo 2008.</ref> ''Ausia'' and ''Burykhia'' lived in shallow coastal waters slightly more than 555 to 548&nbsp;million years ago, and are believed to be the oldest evidence of the chordate lineage of metazoans.<ref name=Oslo_2008/> The Russian Precambrian fossil ''[[Yarnemia]]'' is identified as a tunicate only tentatively, because its fossils are nowhere near as well-preserved as those of ''Ausia'' and ''Burykhia'', so this identification has been questioned.

Fossils of tunicates are rare because their bodies decay soon after death, but in some tunicate families, microscopic spicules are present, which may be preserved as microfossils. These spicules have occasionally been found in Jurassic and later rocks, but, as few palaeontologists are familiar with them, they may have been mistaken for [[sponge spicule]]s.<ref>{{cite web |url=http://www.ucmp.berkeley.edu/chordata/urochordata.html |title=Introduction to the Urochordata |publisher=University of California Museum of Paleontology |access-date=2013-04-07 |archive-url=https://web.archive.org/web/20090421215035/http://www.ucmp.berkeley.edu/chordata/urochordata.html |archive-date=21 April 2009 |url-status=dead }}</ref>

In the Permian and the Triassic, there were also forms with a calcareous exoskeleton. At first, they were mistaken for corals.<ref>[https://www.cambridge.org/core/services/aop-cambridge-core/content/view/0FE5DCCCDFDD464B92DCA4AF68F36F2B/S0022336019001094a.pdf/rare_case_of_an_evolutionary_late_and_ephemeral_biomineralization_tunicates_with_composite_calcareous_skeletons.pdf A rare case of an evolutionary late and ephemeral biomineralization: tunicates with composite calcareous skeletons]</ref><ref>{{Cite journal |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12356 |title=The first tunicate with a calcareous exoskeleton (Upper Triassic, northern Italy) |first=Jobst |last=Wendt |editor-first=Michael |editor-last=Hautmann |date=25 July 2018 |journal=Palaeontology |volume=61 |issue=4 |pages=575–595 |via=CrossRef |doi=10.1111/pala.12356|bibcode=2018Palgy..61..575W |s2cid=135456629 |url-access=subscription }}</ref>

===Hybridization studies===

A multi-taxon [[Molecular phylogenetics|molecular study]] in 2010 proposed that sea squirts are descended from a hybrid between a chordate and a [[protostome]] ancestor (before the divergence of [[panarthropod]]s and [[nematode]]s). This study was based on a quartet partitioning approach designed to reveal [[horizontal gene transfer]] events among metazoan phyla.<ref>{{cite journal |author1=Syvanen, M. |author2=Ducore, J. |year=2010 |title=Whole genome comparisons reveals a possible chimeric origin for a major metazoan assemblage |journal=Journal of Biological Systems |volume=18 |pages=261–275 |doi=10.1142/S0218339010003408 |issue=2 }}</ref>