Spiralia

{{short description|Clade of protostomes with spiral cleavage during early development}}

{{Automatic taxobox

| fossil_range = {{fossil range|Cambrian|Recent|earliest = 558|ref={{Cite journal |last=Telford |first=Maximilian J. |date=2019 |title=Evolution: Arrow Worms Find Their Place on the Tree of Life|journal=Current Biology |volume=29 |issue=5 |pages=R152–R154 |doi=10.1016/j.cub.2018.12.029 |pmid=30836082 |doi-access=free}}}} Possible Ediacaran fossil{{The Rise and Fall of the Ediacaran Biota|chapter=New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications|author=Fedonkin, M.A. |author2=Simonetta, A |author3=Ivantsov, A.Y. |pages=157–179 |doi=10.1144/SP286.12}}

| image = Spiralia clade.jpg

| image_caption =

| display_parents = 5

| taxon = Spiralia

| authority = sensu Edgecombe et al. 2011

| subdivision_ranks = Clades

| subdivision = *Gnathifera

Platytrochozoa

}}

The Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa.{{Cite journal |last=Giribet |first=G. |title=Assembling the lophotrochozoan (=spiralian) tree of life |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=363 |issue=1496 |pages=1513–22 |date=April 2008 |pmid=18192183 |pmc=2614230 |doi=10.1098/rstb.2007.2241 }} The term Spiralia is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most members of the Lophotrochozoa.{{Cite web |url=http://science.kennesaw.edu/~jdirnber/InvertZoo/Tree/Explanations.html |title=Explanations.html |access-date=2009-06-28 |archive-url=https://web.archive.org/web/20130207074145/http://science.kennesaw.edu/%7Ejdirnber/InvertZoo/Tree/Explanations.html |archive-date=2013-02-07 |url-status=dead }}

Distribution of spiralian development across phylogeny

Members of the molluscs, annelids, platyhelminths and nemerteans have all been shown to exhibit spiral cleavage in its classical form. Other spiralian phyla (rotifers, brachiopods, phoronids, gastrotrichs, and bryozoans) are also said to display a derived form of spiral cleavage in at least a portion of their constituent species, although evidence for this is sparse.{{cite journal|last=Hejnol|first=A.|title=A Twist in Time—The Evolution of Spiral Cleavage in the Light of Animal Phylogeny|journal=Integrative and Comparative Biology|date=4 August 2010|volume=50|issue=5|pages=695–706|doi=10.1093/icb/icq103|pmid=21558233|doi-access=}}

Lophotrochozoa within Spiralia

Previously, spiral cleavage was thought to be unique to the Spiralia in the strictest sense—animals such as molluscs and annelids which exhibit classical spiral cleavage. The presence of spiral cleavage in animals such as platyhelminths could be difficult to correlate with some phylogenies.{{cite journal |last=Boyer |first=Barbara C. |author2=Henry, Jonathan Q. |author3=Martindale, Mark Q. |title=Dual Origins of Mesoderm in a Basal Spiralian: Cell Lineage Analyses in the Polyclad Turbellarian Hoploplana inquilina |journal=Developmental Biology |date=1 November 1996 |volume=179 |issue=2 |pages=329–338 |doi=10.1006/dbio.1996.0264 |pmid=8903349|doi-access=free }}

Evidence of a close relationship between molluscs, annelids and lophophorates was found in 1995 and Lophotrochozoa was defined as the group containing these taxa and all the descendants of their last common ancestor.{{cite journal |last=Halanych |first=K. |author2=Bacheller, J. |author3=Aguinaldo, A. |author4=Liva, S. |author5=Hillis, D. |author6=Lake, J. |title=Evidence from 18S ribosomal DNA that the lophophorates are protostome animals |journal=Science |date=17 March 1995 |volume=267 |issue=5204 |pages=1641–1643 |doi=10.1126/science.7886451 |pmid=7886451 |bibcode=1995Sci...267.1641H |s2cid=12196991 }} More recent research has established the Lophotrochozoa as a superphylum within the Metazoa.{{cite journal|last=Dunn|first=C.W. |author2=Hejnol, A. |author3=Matus, D. Q.|author4=Pang, K. |author5=Browne, W. E. |author6=Smith, S.A.|author7=Seaver, E. |author8=Rouse, G.W. |author9=Obst, M. |author10=Sørensen, M. V. |author11=Haddock, S. H. D. |author11-link=Steven Haddock |author12=Schmidt-Rhaesa, A.|author13=Okusu, A. |author14=Kristensen, R.M. |author15=Wheeler, W. C. |author16=Martindale, M. Q. |author17=Giribet, G. |title=Broad phylogenomic sampling improves resolution of the animal tree of life |journal=Nature |date=10 April 2008 |volume=452 |issue=7188 |pages=745–749 |doi=10.1038/nature06614 |pmid=18322464|bibcode=2008Natur.452..745D |s2cid=4397099 }}

With this understanding, the presence of spiral cleavage in polyclad platyhelminths, as well as the more traditional Spiralia, has led to the hypothesis that spiral cleavage was present ancestrally across the Lophotrochozoa as a whole.

With the introduction of Platytrochozoa and Rouphozoa, the cladogram is as follows, with an indication approximately how many million years ago (Mya) the clades radiated into newer clades.{{cite book | chapter-url = https://www.researchgate.net/publication/281209169 | chapter = Assembling the spiralian tree of life| title = Animal Evolution — Genomes, Fossils, and Trees |year=2009 |editor1-last=Telford |editor1-first=MJ |editor2-last=Littlewood |editor2-first=DT |last1=Giribet |first1=G |last2=Dunn |first2=CW |last3=Edgecombe |first3=GD |last4=Hejnol |first4=A |last5=Martindale |first5=MQ |last6=Rouse |first6=GW |pages=52–64}}{{Cite journal |last1=Struck |first1=Torsten H. |last2=Wey-Fabrizius |first2=Alexandra R. |last3=Golombek|first3=Anja |last4=Hering |first4=Lars |last5=Weigert |first5=Anne |last6=Bleidorn |first6=Christoph |last7=Klebow |first7=Sabrina |last8=Iakovenko |first8=Nataliia |last9=Hausdorf |first9=Bernhard |date=July 2014 |title=Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia |journal=Molecular Biology and Evolution |volume=31 |issue=7 |pages=1833–1849 |doi=10.1093/molbev/msu143 |pmid=24748651|doi-access=free }}{{Cite journal |last1=Peterson |first1=Kevin J.|last2=Cotton |first2=James A. |last3=Gehling |first3=James G.|last4=Pisani |first4=Davide |date=2008-04-27 |title=The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records |journal=Philosophical Transactions of the Royal Society of London B: Biological Sciences |volume=363 |issue=1496 |pages=1435–1443 |doi=10.1098/rstb.2007.2233 |pmid=18192191 |pmc=2614224}}{{Cite book |last1=Hankeln |first1=Thomas |last2=Wey-Fabrizius |first2=Alexandra |last3=Herlyn |first3=Holger |last4=Witek |first4=Alexander |last5=Weber |first5=Mathias |last6=Nesnidal |first6=Maximilian |last7=Struck |first7=Torsten |year=2014 |chapter=Phylogeny of platyzoan taxa based on molecular data |title=Deep Metazoan Phylogeny: The Backbone of the Tree of Life |publisher=Walter de Gruyter GmbH |editor1-first=J. Wolfgang |editor1-last=Wägele |editor2-first=Thomas |editor2-last=Bartolomaeus |pages=105–125 |chapter-url=https://www.researchgate.net/publication/262676142}}{{Cite journal |last1=Laumer |first1=Christopher E.|last2=Bekkouche |first2=Nicolas |last3=Kerbl |first3=Alexandra |last4=Goetz |first4=Freya|last5=Neves |first5=Ricardo C. |last6=Sørensen|first6=Martin V. |last7=Kristensen |first7=Reinhardt M. |last8=Hejnol |first8=Andreas |last9=Dunn |first9=Casey W. |title=Spiralian Phylogeny Informs the Evolution of Microscopic Lineages |journal=Current Biology |volume=25 |issue=15 |pages=2000–2006 |doi=10.1016/j.cub.2015.06.068 |pmid=26212884 |year=2015 |doi-access=free}}{{Cite journal |last1=Lu |first1=Tsai-Ming |last2=Kanda |first2=Miyuki |last3=Satoh |first3=Noriyuki |last4=Furuya |first4=Hidetaka |date=2017-05-29 |title=The phylogenetic position of dicyemid mesozoans offers insights into spiralian evolution |journal=Zoological Letters |volume=3 |pages=6 |doi=10.1186/s40851-017-0068-5 |pmid=28560048 |pmc=5447306 |doi-access=free }}{{Cite journal |last1=Luo |first1=Yi-Jyun |last2=Kanda |first2=Miyuki |last3=Koyanagi |first3=Ryo |last4=Hisata |first4=Kanako |last5=Akiyama |first5=Tadashi |last6=Sakamoto |first6=Hirotaka |last7=Sakamoto |first7=Tatsuya |last8=Satoh |first8=Noriyuki |date=2017-12-04 |title=Nemertean and phoronid genomes reveal lophotrochozoan evolution and the origin of bilaterian heads |journal=Nature Ecology and Evolution |volume=2 |issue=1 |pages=141–151 |doi=10.1038/s41559-017-0389-y |pmid=29203924 |doi-access=free }}

{{Clade|style=font-size:85%;line-height:85%|label1=Protostomia|sublabel1=610 mya

|1={{clade

|1=Ecdysozoa 70px

|2=Kimberella †

|label3=Spiralia

|3={{clade

|1=Gnathifera 70 px

|label2=Platytrochozoa|sublabel2=580 mya

|2={{clade

|1={{clade

|1=Mesozoa 40px

|label2=Rouphozoa

|2={{clade

|1=Gastrotricha 60px

|2=Platyhelminthes 65px

}}

|label2=Lophotrochozoa

|2={{clade

|1=Annelida 60px

|2=Mollusca 60px

|label3=Kryptotrochozoa

|3={{clade

|label1=Lophophorata

|1={{clade

|label1=Brachiozoa

|1={{clade

|1=Brachiopoda 60px

|2=Phoronida 50px

}}

|2={{clade

|state1=dashed

|1={{clade

|1=Entoprocta 60px

|2=Cycliophora 30px }}

|2=Ectoprocta (Bryozoa) 60px

}}

|2=Nemertea 40px

}}

}}}}

An alternative phylogeny was given in 2019, with a basal grouping Mollusca with Entoprocta grouping named Tetraneuralia, and a second grouping of Nemertea with Platyhelminthes named Parenchymia as sister of Annelida. In their proposal and according to the original definition, Lophotrochozoa may become a senior synonym for Platytrochozoa.{{Cite journal |last5=Rokhsar |first5=Daniel S. |last4=Satoh |first4=Noriyuki |last3=Goto |first3=Taichiro |last2=Peijnenburg |first2=Katja T. C. A. |last1=Marlétaz |first1=Ferdinand |date=2019-01-10 |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 |issn=0960-9822 |doi-access=free}}{{Cite journal |last6=Lake |first6=J. A. |last5=Hillis |first5=D. M. |last4=Liva |first4=S. M. |last3=Aguinaldo |first3=A. M.|last2=Bacheller |first2=J. D. |last1=Halanych |first1=K. M. |date=1995-03-17 |title=Evidence from 18S ribosomal DNA that the lophophorates are protostome animals |journal=Science |volume=267 |issue=5204 |pages=1641–1643 |doi=10.1126/science.7886451 |issn=1095-9203 |pmid=7886451 |bibcode=1995Sci...267.1641H|s2cid=12196991 }}{{Cite journal |last1=Wanninger |first1=Andreas |last2=Wollesen |first2=Tim |date=2019 |title=The evolution of molluscs: The evolution of molluscs|journal=Biological Reviews |volume=94 |issue=1 |pages=102–115 |doi=10.1111/brv.12439 |pmc=6378612 |pmid=29931833}}

In 2019 the Rouphozoa was recovered again as a basal Platytrochozoa clade.{{Cite journal |last1=Laumer |first1=Christopher E. |last2=Fernández |first2=Rosa |last3=Lemer |first3=Sarah |last4=Combosch|first4=David |last5=Kocot |first5=Kevin M. |last6=Riesgo |first6=Ana |last7=Andrade |first7=Sónia C. S. |last8=Sterrer |first8=Wolfgang |last9=Sørensen |first9=Martin V. |last10=Giribet |first10=Gonzalo |date=2019-07-10 |title=Revisiting metazoan phylogeny with genomic sampling of all phyla|journal=Proceedings of the Royal Society B: Biological Sciences |volume=286 |issue=1906 |pages=20190831 |doi=10.1098/rspb.2019.0831 |issn=0962-8452 |pmc=6650721 |pmid=31288696}}

A 2022 study supported the Trochozoa and Platyzoa hypotheses, as shown below.{{Cite journal |last1=Drábková |first1=Marie |last2=Kocot |first2=Kevin M. |last3=Halanych |first3=Kenneth M. |last4=Oakley |first4=Todd H. |last5=Moroz |first5=Leonid L. |last6=Cannon |first6=Johanna T. |last7=Kuris |first7=Armand |last8=Garcia-Vedrenne |first8=Ana Elisa |last9=Pankey |first9=M. Sabrina |last10=Ellis |first10=Emily A. |last11=Varney |first11=Rebecca |last12=Štefka |first12=Jan |last13=Zrzavý |first13=Jan |date=2022-07-13 |title=Different phylogenomic methods support monophyly of enigmatic 'Mesozoa' (Dicyemida + Orthonectida, Lophotrochozoa) |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=289 |issue=1978 |pages=20220683 |doi=10.1098/rspb.2022.0683 |issn=0962-8452 |pmc=9257288 |pmid=35858055 }} The same year another study placed bryozoans, entoproctans and cycliophorans in the group Polyzoa as one of the earliest branches among Lophotrochozoa.[https://www.science.org/doi/10.1126/sciadv.abo4400 Polyzoa is back: The effect of complete gene sets on the placement of Ectoprocta and Entoprocta - Science]

{{Clade|style=font-size:85%;line-height:85%|label1=Protostomia|1={{clade

|1=Ecdysozoa 70px

|label2=Spiralia

|2={{clade

|label1=Trochozoa

|1={{clade

|1=Mollusca 60px

|2={{clade

|1=Nemertea 40px

|2=Annelida 60px

|label3=Brachiozoa

|3={{clade