Editing Bryozoa (section)

=== Evolutionary family tree ===
[[File:OrdovicianEdrio.jpg |thumb |right |An Upper [[Ordovician]] cobble with the [[edrioasteroid]] ''Cystaster stellatus'' and the thin branching cyclostome bryozoan ''Corynotrypa''. Kope Formation, northern Kentucky, United States.]]
Scientists are divided about whether the Bryozoa (Ectoprocta) are a [[monophyletic]] group (whether they include all and only a single ancestor species and all its descendants), about what are the phylum's closest relatives in the family tree of animals, and even about whether they should be regarded as members of the [[protostome]]s or [[deuterostome]]s, the two major groups that account for all moderately complex animals.

Molecular phylogeny, which attempts to work out the evolutionary family tree of organisms by comparing their [[biochemistry]] and especially their [[gene]]s, has done much to clarify the relationships between the better-known [[invertebrate]] phyla.<ref name="Halanych2004AnimalPhylogeny" /> However, the shortage of genetic data about "minor phyla" such as bryozoans and [[Entoprocta|entoprocts]] has left their relationships to other groups unclear.<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics">{{cite journal |last1=Hausdorf |first1=B. |year=2007 |title=Spiralian Phylogenomics Supports the Resurrection of Bryozoa Comprising Ectoprocta and Entoprocta |journal=Molecular Biology and Evolution |volume=24 |issue=12 |pages=2723–2729 |doi=10.1093/molbev/msm214 |pmid=17921486 |last2=Helmkampf |first2=M. |last3=Meyer |first3=A. |last4=Witek |first4=A. |last5=Herlyn |first5=H. |last6=Bruchhaus |first6=I. |last7=Hankeln |first7=T. |last8=Struck |first8=T.H. |last9=Lieb |first9=B. |doi-access=free}}</ref>

====Traditional view====
The traditional view is that the Bryozoa are a monophyletic group, in which the class [[Phylactolaemata]] is most closely related to [[Stenolaemata]] and [[Ctenostomatida]], the [[Class (biology)|classes]] that appear earliest in the fossil record.<ref name="WoodLore2005PhylactolaemateMolPhylo" /> However, in 2005 a [[molecular phylogeny]] study that focused on phylactolaemates concluded that these are more closely related to the phylum [[Phoronid]]a, and especially to the only phoronid species that is colonial, than they are to the other ectoproct classes. That implies that the Entoprocta are not monophyletic, as the Phoronida are a sub-group of ectoprocts but the standard definition of Entoprocta excludes the Phoronida.<ref name="WoodLore2005PhylactolaemateMolPhylo" />

[[File:Ropalonaria large 010213.jpg|thumb|''Ropalonaria venosa'', an etching [[trace fossil]] of a Late Ordovician ctenostome bryozoan on a strophomenid [[brachiopod]] valve; Cincinnatian of southeastern Indiana, United States.<ref>{{cite journal |last= Pohowsky |first=R.A. |year= 1978 |title=The boring ctenostomate bryozoa: taxonomy and paleobiology based on cavities in calcareous substrata |journal=Bulletins of American Paleontology |volume=73 |pages=192p}}</ref>]]
In 2009 another [[molecular phylogeny]] study, using a combination of genes from [[mitochondria]] and the [[cell nucleus]], concluded that Bryozoa is a [[monophyletic]] phylum, in other words includes all the descendants of a common ancestor that is itself a bryozoan. The analysis also concluded that the [[class (biology)|classes]] Phylactolaemata, [[Stenolaemata]] and [[Gymnolaemata]] are also monophyletic, but could not determine whether [[Stenolaemata]] are more closely related to [[Phylactolaemata]] or [[Gymnolaemata]]. The Gymnolaemata are traditionally divided into the soft-bodied [[Ctenostomatida]] and [[biomineralization|mineralized]] Cheilostomata, but the 2009 analysis considered it more likely that neither of these [[order (biology)|orders]] is monophyletic and that mineralized [[skeleton]]s probably evolved more than once within the early Gymnolaemata.<ref name="FuchsObstSundberg2009ComprMolPhyloOfBryozoa">{{cite journal |last1=Fuchs |first1=J. |date=July 2009 |title=The first comprehensive molecular phylogeny of Bryozoa (Ectoprocta) based on combined analyses of nuclear and mitochondrial genes |journal=Molecular Phylogenetics and Evolution |volume=52 |issue=1 |pages=225–233 |doi=10.1016/j.ympev.2009.01.021 |pmid=19475710 |last2=Obst |first2=M. |last3=Sundberg |first3=P|bibcode=2009MolPE..52..225F }}</ref>

Bryozoans' relationships with other phyla are uncertain and controversial. Traditional phylogeny, based on [[anatomy]] and on the development of the adult forms from [[embryo]]s, has produced no enduring consensus about the position of ectoprocts.<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> Attempts to reconstruct the family tree of animals have largely ignored ectoprocts and other "minor phyla", which have received little scientific study because they are generally tiny, have relatively simple body plans, and have little impact on human economies – despite the fact that the "minor phyla" include most of the variety in the evolutionary history of animals.<ref>{{cite journal |last1=Garey |first1=J.R. |year=1998 |title=The Essential Role of "Minor" Phyla in Molecular Studies of Animal Evolution |journal=American Zoologist |volume=38 |issue=6 |pages=907–917 |doi=10.1093/icb/38.6.907 |last2=Schmidt-Rhaesa |first2=Andreas |doi-access=free}}</ref>

In the opinion of Ruth Dewel, Judith Winston, and Frank McKinney, "Our standard interpretation of bryozoan [[morphology (biology)|morphology]] and [[embryology]] is a construct resulting from over 100 years of attempts to synthesize a single framework for all invertebrates," and takes little account of some peculiar features of ectoprocts.<ref name="DewelWinstonMcKinney2001Deconstructing" />

[[File:Phaenopora superba Silurian Brassfield.jpeg|thumb|''Phaenopora superba'', a ptilodictyine bryozoan from the Silurian of [[Ohio]], United States]]
[[File:Sucoretepora.jpg|thumb|The flat, branching bryozoan ''Sulcoretepora'', from the Middle Devonian of [[Wisconsin]], United States]]

In ectoprocts, all of the larva's internal organs are destroyed during the metamorphosis to the adult form and the adult's organs are built from the larva's [[Epidermis (skin)|epidermis]] and [[mesoderm]], while in other [[bilateria]]ns some organs including the gut are built from [[endoderm]]. In most bilaterian embryos the blastopore, a dent in the outer wall, deepens to become the larva's gut, but in ectoprocts the blastopore disappears and a new dent becomes the point from which the gut grows. The ectoproct coelom is formed by neither of the processes used by other bilaterians, [[enterocoely]], in which pouches that form on the wall of the gut become separate cavities, nor [[schizocoely]], in which the tissue between the gut and the body wall splits, forming paired cavities.<ref name="DewelWinstonMcKinney2001Deconstructing">{{cite book |last=Dewel |first=R.A. |author2=Winston, J.E. |author3=McKinney, F.J. |others=M.E. |title=Bryozoan studies 2001: proceedings of the Twelfth International Bryozoology Conference |editor=Wyse Jacksdon, P.E. |editor2=Buttler, C.E. |editor3=Spencer Jones, M.E. |publisher=Swets and Zeitlinger |location=Lisse |year=2002 |pages=93–96 |chapter=Deconstructing byozoans: origin and consequences of a unique body plan |isbn=978-90-5809-388-2 |chapter-url=https://books.google.com/books?id=4-jlUfCMlQkC&q=ectoprocta%20bryozoa%20phylogeny&pg=PA93 |access-date=2009-08-13 |archive-date=8 March 2023 |archive-url=https://web.archive.org/web/20230308183244/https://books.google.com/books?id=4-jlUfCMlQkC&q=ectoprocta%20bryozoa%20phylogeny&pg=PA93 |url-status=live }}</ref>

====Entoprocts====

When entoprocts were discovered in the 19th century, they and bryozoans (ectoprocts) were regarded as classes within the phylum Bryozoa, because both groups were [[Sessility (zoology)|sessile]] animals that [[filter feeder|filter-fed]] by means of a crown of tentacles that bore [[cilia]].

From 1869 onwards increasing awareness of differences, including the position of the entoproct [[anus]] inside the feeding structure and the difference in the early [[Cleavage (embryo)|pattern of division]] of cells in their [[embryo]]s, caused scientists to regard the two groups as separate phyla,<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics" /> and "Bryozoa" became just an alternative name for ectoprocts, in which the anus is outside the feeding organ.<ref name="Halanych2004AnimalPhylogeny" /> A series of molecular phylogeny studies from 1996 to 2006 have also concluded that bryozoans (ectoprocts) and entoprocts are not sister groups.<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics" />

However, two well-known zoologists, Claus Nielsen and [[Thomas Cavalier-Smith]], maintain on anatomical and developmental grounds that bryozoans and entoprocts are member of the same phylum, Bryozoa. A molecular phylogeny study in 2007 also supported this old idea, while its conclusions about other phyla agreed with those of several other analyses.<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics" />

====Grouping into the Lophophorata====

By 1891 bryozoans (ectoprocts) were grouped with [[phoronid]]s in a super-phylum called "Tentaculata". In the 1970s comparisons between phoronid larvae and the [[cyphonautes]] larva of some gymnolaete bryozoans produced suggestions that the bryozoans, most of which are colonial, evolved from a semi-colonial species of phoronid.<ref name="Nielsen2001AnimalEvoPhylumEctoprocta">{{cite book |last=Nielsen |first=C. |title=Animal evolution: interrelationships of the living phyla |publisher=Oxford University Press |year=2001 |edition=2 |pages=244–264 |chapter=Phylum Ectoprocta |isbn=978-0-19-850681-2 |chapter-url=https://books.google.com/books?id=UmCg6c0HkqMC&q=ectoprocta%20bryozoa%20phylogeny&pg=PA257 |access-date=2009-08-14 |archive-date=8 March 2023 |archive-url=https://web.archive.org/web/20230308183241/https://books.google.com/books?id=UmCg6c0HkqMC&q=ectoprocta%20bryozoa%20phylogeny&pg=PA257 |url-status=live }}</ref> [[Brachiopod]]s were also assigned to the "Tentaculata", which were renamed [[Lophophorata]] as they all use a [[lophophore]] for filter feeding.<ref name="Halanych2004AnimalPhylogeny" />

The majority of scientists accept this,<ref name="Halanych2004AnimalPhylogeny" /> but Claus Nielsen thinks these similarities are superficial.<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda">{{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 }}</ref> The Lophophorata are usually defined as animals with a lophophore, a three-part coelom and a U-shaped gut.<ref name="Nielsen2001AnimalEvoPhylumEctoprocta" /> In Nielsen's opinion, phoronids' and brachiopods' lophophores are more like those of [[pterobranch]]s,<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> which are members of the phylum [[Hemichordata]].<ref>{{cite web |url=http://www.ucmp.berkeley.edu/chordata/hemichordata.html |access-date=2008-09-22 |title=Introduction to the Hemichordata |publisher=University of California Museum of Paleontology |archive-url=https://web.archive.org/web/20190201080336/http://www.ucmp.berkeley.edu/chordata/hemichordata.html |archive-date=1 February 2019 |url-status=dead }}</ref> Bryozoan's tentacles bear cells with multiple [[cilia]], while the corresponding cells of phoronids', brachiopods' and pterobranchs' lophophores have one cilium per cell; and bryozoan tentacles have no hemal canal ("blood vessel"), which those of the other three phyla have.<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" />

If the grouping of bryozoans with phoronids and brachiopods into Lophophorata is correct, the next issue is whether the Lophophorata are [[protostome]]s, along with most invertebrate phyla, or [[deuterostome]]s, along with [[chordate]]s, [[hemichordate]]s and [[echinoderm]]s.

The traditional view was that lophophorates were a mix of protostome and deuterostome features. Research from the 1970s onwards suggested they were deuterostomes, because of some features that were thought characteristic of deuterostomes: a three-part coelom; radial rather than spiral cleavage in the development of the embryo;<ref name="Halanych2004AnimalPhylogeny" /> and formation of the coelom by [[enterocoely]].<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> However the coelom of ectoproct larvae shows no sign of division into three sections,<ref name="Nielsen2001AnimalEvoPhylumEctoprocta" /> and that of adult ectoprocts is different from that of other [[coelomate]] phyla as it is built anew from epidermis and mesoderm after metamorphosis has destroyed the larval coelom.<ref name="DewelWinstonMcKinney2001Deconstructing" />

====Lophophorate molecular phylogenetics====

Molecular phylogeny analyses from 1995 onwards, using a variety of biochemical evidence and analytical techniques, placed the lophophorates as protostomes and closely related to [[annelid]]s and [[mollusc]]s in a super-phylum called [[Lophotrochozoa]].<ref name="Halanych2004AnimalPhylogeny" /><ref name="HelmkampfBruchhausHausdorf2008PhylogenOfLophophorates">{{cite journal |last1=Helmkampf |first1=M. |year=2008 |title=Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept |journal=Proceedings of the Royal Society B: Biological Sciences |volume=275 |pages=1927–1933 |doi=10.1098/rspb.2008.0372 |last2=Bruchhaus |first2=Iris |last3=Hausdorf |first3=Bernhard |pmid=18495619 |issue=1645 |pmc=2593926}}</ref> "Total evidence" analyses, which used both morphological features and a relatively small set of genes, came to various conclusions, mostly favoring a close relationship between lophophorates and Lophotrochozoa.<ref name="HelmkampfBruchhausHausdorf2008PhylogenOfLophophorates" /> A study in 2008, using a larger set of genes, concluded that the lophophorates were closer to the Lophotrochozoa than to deuterostomes, but also that the lophophorates were not monophyletic. Instead, it concluded that brachiopods and phoronids formed a monophyletic group, but bryozoans (ectoprocts) were closest to entoprocts, supporting the original definition of "Bryozoa".<ref name="HelmkampfBruchhausHausdorf2008PhylogenOfLophophorates" />

They are the only major phylum of exclusively clonal animals, composed of modular units known as zooids. Because they thrive in colonies, colonial growth allows them to develop unrestricted variations in form. Despite this, only a small number of basic growth forms have been found and have commonly reappeared throughout the history of the bryozoa.<ref name="Bryozoan Evolution" />

{{clade
|label1=[[Lophotrochozoa]]
|1={{clade
   |1=[[Cycliophora]] <span style="{{MirrorH}}">[[File:CYC-000044 hab Symbion Z5v2v5N.png|70px]]</span>
   |2=[[Annelida]] [[File:Polychaeta (no) 2.jpg|70px]]
   |3={{clade
      |1=[[Mollusca]] <span style="{{MirrorH}}">[[File:Grapevinesnail 01a.jpg|65px]]</span>
      |label2=<!--[[Kryptotrochozoa]]-->
      |2={{clade
         |label1=[[Lophophorata]]
         |1={{clade
            |label1=[[Brachiozoa]]
            |1={{clade
               |1=[[Brachiopoda]] [[File:LingulaanatinaAA_(cropped).JPG|60px]]
               |2=[[Phoronida]] <span style="{{MirrorH}}">[[File:Phoronopsis harmeri IZ 1643662.png|70px]]</span>
               }}
            |label2='''Bryozoa''' [[sensu lato|''s.l.'']]
            |2={{clade
               |1='''[[Entoprocta]]''' [[File:Barentsia laxa 1498941 (no background).png|80px]]
               |2='''[[Ectoprocta]]''' [[File:Bugulina flabellata 272067784.png|70px]]
               }}
            }}
         }}
      }}
   }}
}}

====Ectoproct molecular phylogenetics====
The phylogenetic position of the ectoproct bryozoans remains uncertain, but it remains certain that they belong to the Protostomia and more specifically to the Lophotrochozoa. This implies that the ectoproct larva is a trochophore with the corona being a homologue of the prototroch; this is supported from the similarity between the coronate larvae and the Type 1 pericalymma larvae of some molluscs and sipunculans, where the prototroch zone is expanded to cover the hyposphere.<ref>{{cite journal |last1=Nielsen |first1=C. |last2=Worsaae |first2=K. |title=Structure and occurrence of cyphonautes larvae (Bryozoa, Ectoprocta) |journal=Journal of Morphology |date=September 2010 |volume=271 |issue=9 |pages=1094–1109 |doi=10.1002/jmor.10856 |pmid=20730922 |s2cid=11453241}}</ref>

A study of the mitochondrial DNA sequence suggests that the Bryozoa may be related to the [[Chaetognatha]].<ref name=Shen2012>{{cite journal |author1=Shen, X. |author2=Tian, M. |author3=Meng, X. |author4=Liu, H. |author5=Cheng, H. |author6=Zhu, C. |author7=Zhao, F. |title=Complete mitochondrial genome of ''Membranipora grandicella'' (Bryozoa: Cheilostomatida) determined with next-generation sequencing: The first representative of the suborder Malacostegina |journal=Comparative Biochemistry and Physiology Part D: Genomics and Proteomics |date=September 2012 |volume=7 |issue=3 |pages=248–253 |doi=10.1016/j.cbd.2012.03.003 |pmid=22503287}}</ref>