Editing Bryozoa

{{Short description|Phylum of colonial aquatic invertebrates called moss animals}}
{{Redirect|Polyzoa|the tunicate genus|Polyzoa (tunicate)}}
{{Good article}}
{{Use dmy dates|date=September 2015}}
{{Automatic taxobox
| fossil_range = {{fossil range|earliest=Early Cambrian|Ordovician| Recent|ref=<ref name=Taylor2013/><ref>{{cite journal |last1=Ma |first1=Junye |last2=Taylor |first2=Paul D. |last3=Xia |first3=Fengsheng |last4=Zhan |first4=Renbin |date=September 2015 |title=The oldest known bryozoan: ''Prophyllodictya'' (Cryptostomata) from the lower Tremadocian (Lower Ordovician) of Liujiachang, south-western Hubei, central China |journal=Palaeontology |volume=58 |issue=5 |pages=925–934 |doi=10.1111/pala.12189 |bibcode=2015Palgy..58..925M |s2cid=130040324 |doi-access=free }}</ref>}} {{small|Contested Cambrian records (''[[Pywackia]]'', ''[[Protomelission]]''<ref name=s41586-023-05775-5/>)}}
| image = Haeckel Bryozoa.jpg
| image_upright = 1.1
| image_caption = "Bryozoa", from [[Ernst Haeckel]]'s {{lang|de|[[Kunstformen der Natur]]}}, 1904
| taxon = Bryozoa
| authority = [[Christian Gottfried Ehrenberg|Ehrenberg]], 1831<ref>{{cite journal |last=Ernst |first=A. |year=2007 |title=A cystoporate bryozoan species from the Zechstein (Late Permian) |journal=Paläontologische Zeitschrift |volume=81 |issue=2 |pages=113–117 |doi=10.1007/BF02988385 |bibcode=2007PalZ...81..113E |s2cid=129637643}}</ref>
| subdivision_ranks = Classes
| subdivision = [[#Classification and diversity|See text]].
| synonyms = Ectoprocta (Nitsche, 1869) (formerly subphylum of Bryozoa)
| synonyms_ref = <ref name="FuchsObstSundberg2009ComprMolPhyloOfBryozoa" />
}}

'''Bryozoa''' (also known as the '''Polyzoa''', '''Ectoprocta''' or commonly as '''moss animals''')<ref name=Brusaca>{{cite book |last=Brusca |first=Richard C. |year=1980 |orig-year=1973 |title=Common intertidal invertebrates of the Gulf of California |chapter=21: The Lophophorate Phyla |edition=revised & expanded, 2nd |place=Tucson, AZ |publisher=University of Arizona Press |isbn=9780816506828 |oclc=1029265317 |chapter-url=https://archive.org/details/commonintertidal00brus |chapter-url-access=registration}}</ref> are a [[phylum]] of simple, [[aquatic animal|aquatic]] [[invertebrate]] animals, nearly all living in sedentary [[Colony (biology)|colonies]]. Typically about {{convert|0.5|mm|in|frac=64}} long, they have a special feeding structure called a [[lophophore]], a "crown" of tentacles used for [[filter feeder|filter feeding]]. Most [[Marine (ocean)|marine]] bryozoans live in tropical waters, but a few are found in [[oceanic trench]]es and polar waters. The bryozoans are classified as the [[Stenolaemata|marine bryozoans]] (Stenolaemata), [[Phylactolaemata|freshwater bryozoans]] (Phylactolaemata), and [[Gymnolaemata|mostly-marine bryozoans]] (Gymnolaemata), a few members of which prefer [[brackish water]]. 5,869{{nbsp}}living species are known.<ref name=Bock2013>{{cite journal |last1=Bock |first1=P. |last2=Gordon |first2=D.P. |date=August 2013 |title=Phylum Bryozoa {{small|Ehrenberg, 1831}} |journal=Zootaxa |volume=3703 |issue=1 |pages=67–74 |doi=10.11646/zootaxa.3703.1.14 |url=https://www.researchgate.net/publication/279928935}}</ref> Originally all of the crown group Bryozoa were colonial, but as an adaptation to a mesopsammal (interstitial spaces in marine sand) life or to deep-sea habitats, secondarily solitary forms have since evolved. Solitary species have been described in four [[genus|genera]]; (''Aethozooides'', ''Aethozoon'', ''Franzenella'' and ''[[Monobryozoon]]''). The latter having a statocyst-like organ with a supposed excretory function.<ref>{{Cite journal |last1=Schwaha |first1=Thomas F. |last2=Ostrovsky |first2=Andrew N. |last3=Wanninger |first3=Andreas |date=June 2020 |title=Key novelties in the evolution of the aquatic colonial phylum Bryozoa: evidence from soft body morphology |journal=Biological Reviews of the Cambridge Philosophical Society |volume=95 |issue=3 |pages=696–729 |doi=10.1111/brv.12583 |pmc=7317743 |pmid=32032476}}</ref><ref>{{Cite journal |last1=Schwaha |first1=Thomas |last2=Bernhard |first2=Joan M. |last3=Edgcomb |first3=Virginia P. |last4=Todaro |first4=M. Antonio |date=2019-08-01 |title=Aethozooides uraniae, a new deep-sea genus and species of solitary bryozoan from the Mediterranean Sea, with a revision of the Aethozoidae |url=https://doi.org/10.1007/s12526-019-00948-w |journal=Marine Biodiversity |language=en |volume=49 |issue=4 |pages=1843–1856 |doi=10.1007/s12526-019-00948-w|bibcode=2019MarBd..49.1843S |hdl=11380/1174838 |hdl-access=free }}</ref>

The terms Polyzoa and Bryozoa were introduced in 1830 and 1831, respectively.<ref name=Thompson1830>{{cite book |last=Thompson |first=John V. |year=1830 |title=Zoological researches and illustrations; or Natural history of nondescript or imperfectly known animals |chapter=Memoir V: On Polyzoa, a new animal discovered as an inhabitant of some Zoophites |publisher=King and Ridings |place=Cork, IE |pages=89–102 |chapter-url=https://archive.org/details/thompson-1830zoologicalresear-00thom |url=https://archive.org/details/zoologicalresear00thom}}</ref><ref>{{cite book |last=Ehrenberg |first=Christian G. |year=1831 |title=Symbolae physicae, seu lcones et descriptiones corporum naturalium novorum aut minus cognitorum. |chapter=Pars zoologica. Animalia evertebrata exclusis insectis [Invertebrata other than Insecta] |language=la |publisher=Berolini Ex officina Academica |pages=1–126 |chapter-url=https://archive.org/details/SymbolaephysicaAnimEhre}}</ref> Soon after it was named, another group of animals was discovered whose filtering mechanism looked similar, so it was included in Bryozoa until 1869, when the two groups were noted to be very different internally. The new group was given the name "[[Entoprocta]]", while the original Bryozoa were called "Ectoprocta". Disagreements about terminology persisted well into the 20th century, but "Bryozoa" is now the generally accepted term.<ref name=Stebbing1911>{{cite journal |last=Stebbing |first=T.R.R. |year=1911 |title=The terms Polyzoa and Bryozoa |journal=Proceedings of the Linnean Society of London |volume=Session 123 (Symposium) |pages=61–72 |url=https://archive.org/details/stebbing-1911-proceedingsoflin-190912linn}}</ref><ref name="Muir-Wood 1955">{{cite book |last=Muir-Wood |first=H.M. |date=1955 |title=A history of the classification of the phylum Brachiopoda |page=13 |publisher=British Museum (Natural History) |place=London| url=https://archive.org/details/muir-wood-classification-brachiopoda}}</ref>

Colonies take a variety of forms, including fans, bushes and sheets. Single animals, called [[zooid]]s, live throughout the colony and are not fully independent. These individuals can have unique and diverse functions. All colonies have "autozooids", which are responsible for feeding, [[excretion]], and supplying nutrients to the colony through diverse channels. Some classes have specialist zooids like hatcheries for fertilized eggs, colonial defence structures, and root-like attachment structures. [[Cheilostomata]] is the most [[species diversity|diverse]] [[order (biology)|order]] of bryozoan, possibly because its members have the widest range of specialist zooids. They have [[biomineralization|mineralized]] exoskeletons and form single-layered sheets which encrust over surfaces, and some colonies can creep very slowly by using spiny defensive zooids as legs.

Each zooid consists of a "cystid", which provides the body wall and produces the [[exoskeleton]], and a "[[polypide]]", which holds the organs. Zooids have no special excretory organs, and autozooids' polypides are scrapped when they become overloaded with waste products; usually the body wall then grows a replacement polypide. Their gut is U-shaped, with the mouth inside the crown of tentacles and the anus outside it. Zooids of all the freshwater species are simultaneous [[hermaphrodite]]s. Although those of many marine species function first as males and then as females, their colonies always contain a combination of zooids that are in their male and female stages. All species emit [[sperm]] into the water. Some also release [[ovum|ova]] into the water, while others capture sperm via their tentacles to fertilize their ova internally. In some species the [[larva]]e have large [[yolk]]s, go to feed, and quickly settle on a surface. Others produce larvae that have little yolk but swim and feed for a few days before settling. After settling, all larvae undergo a radical [[metamorphosis]] that destroys and rebuilds almost all the internal tissues. Freshwater species also produce [[statoblast]]s that lie dormant until conditions are favorable, which enables a colony's lineage to survive even if severe conditions kill the mother colony.

Predators of marine bryozoans include [[nudibranch|sea slug]]s (nudibranchs), fish, [[sea urchin]]s, [[pycnogonid]]s, [[crustacean]]s, [[mite]]s and [[starfish]]. Freshwater bryozoans are preyed on by snails, insects, and fish. In [[Thailand]], many populations of one freshwater species have been wiped out by an [[introduced species]] of snail.<ref name="predation_golden" /> ''[[Membranipora membranacea]]'', a fast-growing invasive bryozoan off the northeast and northwest coasts of the US, has reduced [[kelp forest]]s so much that it has affected local fish and invertebrate populations.<ref name="h057">{{cite book |last=Lauer |first=Antje |title=The Mechanistic Benefits of Microbial Symbionts |date=2016 |publisher=Springer International Publishing |isbn=978-3-319-28066-0 |volume=2 |publication-place=Cham |pages=239–268 |chapter=Watersipora subtorquata and the Possible Role of Its Associated Microbes: An Attempt to Explain the Extraordinary Invasion Success of This Marine Bryozoan Species |series=Advances in Environmental Microbiology |doi=10.1007/978-3-319-28068-4_9 |quote=Occasionally, the impact of an invertebrate invader can be substantial; such has been documented for Membranipora membranacea, a fast-growing invasive bryozoan species which has reduced kelp forests off the northeast and northwest coasts of the USA to an extent that it has affected local fish and invertebrate populations}}</ref> Bryozoans have spread diseases to [[fish farm]]s and fishermen. Chemicals extracted from a marine bryozoan species have been investigated for treatment of cancer and [[Alzheimer's disease]], but analyses have not been encouraging.<ref name=Introduction>{{cite web |title=Introduction to the Bryozoa |publisher=University of California Museum of Paleontology |place=Berkeley, CA |url=https://ucmp.berkeley.edu/bryozoa/bryozoa.html |access-date=8 December 2019 |archive-date=8 December 2019 |archive-url=https://web.archive.org/web/20191208225858/https://ucmp.berkeley.edu/bryozoa/bryozoa.html |url-status=live }}</ref>

Mineralized skeletons of bryozoans first appear in rocks from the Early [[Ordovician]] period,<ref name=Taylor2013>{{cite journal |last1=Taylor |first1=P.D. |last2=Berning |first2=B. |last3=Wilson |first3=M.A. |date=November 2013 |title=Reinterpretation of the Cambrian 'bryozoan' ''Pywackia'' as an octocoral |journal=Journal of Paleontology |volume=87 |issue=6 |pages=984–990 |s2cid=129113026 |doi=10.1666/13-029 |bibcode=2013JPal...87..984T |url=https://zenodo.org/record/907861 |access-date=20 April 2018 |archive-date=7 June 2019 |archive-url=https://web.archive.org/web/20190607161619/https://zenodo.org/record/907861 |url-status=live }}</ref> making it the last major phylum to appear in the fossil record. This has led researchers to suspect that bryozoans arose earlier but were initially unmineralized, and may have differed significantly from fossilized and modern forms. In 2021, some research suggested ''Protomelission'', a genus known from the Cambrian [[Period (geology)|period]], could be an example of an early bryozoan,<ref>{{cite journal |last1=Zhang |first1=Zhiliang |last2=Zhang |first2=Zhifei |last3=Ma |first3=J. |last4=Taylor |first4=P. D. |last5=Strotz |first5=L. C. |last6=Jacquet |first6=S. M. |last7=Skovsted |first7=C. B. |last8=Chen |first8=F. |last9=Han |first9=J. |last10=Brock |first10=G. A. |year=2021 |title=Fossil evidence unveils an early Cambrian origin for Bryozoa |journal=Nature |volume=599 |issue=7884 |pages=251–255 |doi=10.1038/s41586-021-04033-w |pmid=34707285 |pmc=8580826 |bibcode=2021Natur.599..251Z |s2cid=240073948 }}</ref> but later research suggested that this taxon may instead represent a [[Dasycladales|dasyclad]] alga.<ref name=s41586-023-05775-5>{{Cite journal | doi = 10.1038/s41586-023-05775-5 | title = Protomelission is an early dasyclad alga and not a Cambrian bryozoan | journal = Nature | date = 8 March 2023 | first1 = Jie | last1 = Yang | first2 = Tian | last2 = Lan | first3 = Xi-guang | last3 = Zhang | first4 = Martin R. | last4 = Smith| volume = 615 | issue = 7952 | pages = 468–471 | pmid = 36890226 | bibcode = 2023Natur.615..468Y | s2cid = 257425218 | url = https://durham-repository.worktribe.com/file/1182254/1/Accepted%20Journal%20Article }}</ref> Early fossils are mainly of erect forms, but encrusting forms gradually became dominant. It is uncertain whether the phylum is [[monophyletic]]. Bryozoans' evolutionary relationships to other phyla are also unclear, partly because scientists' view of the family tree of animals is mainly influenced by better-known phyla. Both [[morphology (biology)|morphological]] and [[molecular phylogeny]] analyses disagree over bryozoans' relationships with entoprocts, about whether bryozoans should be grouped with [[brachiopod]]s and [[phoronid]]s in [[Lophophorata]], and whether bryozoans should be considered [[protostome]]s or [[deuterostome]]s.

== Description ==

=== Distinguishing features ===

Bryozoans, [[Phoronida|phoronids]] and [[Brachiopoda|brachiopods]] [[Filter feeding|strain food out of the water]] by means of a [[lophophore]], a "crown" of hollow tentacles. Bryozoans form colonies consisting of [[Cloning|clones]] called zooids that are typically about {{cvt|0.5|mm|in|frac=64}} long.<ref name="RuppertFoxBarnesBryozoa" /> Phoronids resemble bryozoan zooids but are {{cvt|2|to|20|cm|in|frac=2}} long and, although they often grow in clumps, do not form colonies consisting of clones.<ref name="RuppertFoxBarnesPhoronida" /> Brachiopods, generally thought to be closely related to bryozoans and phoronids, are distinguished by having shells rather like those of [[bivalve]]s.<ref name="RuppertFoxBarnesBrachiopoda" /> All three of these [[phylum|phyla]] have a [[coelom]], an internal cavity lined by [[mesothelium]].<ref name="RuppertFoxBarnesBryozoa" /><ref name="RuppertFoxBarnesPhoronida" /><ref name="RuppertFoxBarnesBrachiopoda" />
Some encrusting bryozoan colonies with [[biomineralization|mineralized]] [[exoskeleton]]s look very like small corals. However, bryozoan colonies are founded by an ancestrula, which is round rather than shaped like a normal zooid of that species. On the other hand, the founding polyp of a coral has a shape like that of its daughter polyps, and coral zooids have no [[coelom]] or [[lophophore]].<ref name="RichFenton1997Bryozoans" />

[[Entoprocta|Entoprocts]], another phylum of filter-feeders, look rather like bryozoans but their [[lophophore]]-like feeding structure has solid tentacles, their [[anus]] lies inside rather than outside the base of the "crown" and they have no [[coelom]].<ref name="RuppertFoxBarnesEntoprocta" />
{{clear}}
{| class="wikitable"
|+ Summary of distinguishing features
|- align="center"
! rowspan="2"| &nbsp; !! rowspan="2"| Bryozoa<ref name="RuppertFoxBarnesBryozoa" />{{pb}}(Ectoprocta) !! colspan="2" | Other [[lophophorate]]s<ref name="RuppertFoxBarnesLophophorataGen">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Lophoporata | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | page=[https://archive.org/details/isbn_9780030259821/page/817 817] | chapter-url=https://archive.org/details/isbn_9780030259821/page/817 }}</ref>!! Other [[Lophotrochozoa]] !! colspan="2" | Similar-looking phyla
|- align="center"
! [[Phoronida]]<ref name="RuppertFoxBarnesPhoronida">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Lophoporata | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/817 817–821] | chapter-url=https://archive.org/details/isbn_9780030259821/page/817 }}</ref>!! [[Brachiopoda]]<ref name="RuppertFoxBarnesBrachiopoda">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Lophoporata | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/821 821–829] | chapter-url=https://archive.org/details/isbn_9780030259821/page/821 }}</ref>!! [[Annelida]], [[Mollusca]] !! [[Entoprocta]]<ref name="RuppertFoxBarnesEntoprocta">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Kamptozoa and Cycliophora | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/808 808–812] | chapter-url=https://archive.org/details/isbn_9780030259821/page/808 }}</ref>!! [[Coral]]s (class in phylum [[Cnidaria]])<ref name="RichFenton1997Bryozoans" />
|- align="center"
! [[Coelom]]
| Three-part, if the cavity of the epistome is included || colspan="2" | Three-part || One per segment in basic form; merged in some [[taxon|taxa]] || colspan="2" | none
|- align="center"
! Formation of [[coelom]]
| Uncertain because [[metamorphosis]] of larvae into adults makes this impossible to trace || colspan="2" | [[Enterocoely]] || [[Schizocoely]] || colspan="2" | not applicable
|- align="center"
! [[Lophophore]]
| colspan="3" | With hollow tentacles || none || Similar-looking feeding structure, but with solid tentacles || none
|- align="center"
! Feeding current
| colspan="3" | From tips to bases of tentacles || not applicable || From bases to tips of tentacles || not applicable
|- align="center"
! [[Cilia|Multiciliated]] cells in [[epithelium]]
| Yes<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> || colspan="2" | no<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> || colspan="2" | Yes<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> || not applicable
|- align="center"
! Position of [[anus]]
| colspan="2" | Outside base of [[lophophore]] || Varies, none in some species || Rear end, but none in [[Siboglinidae]] || Inside base of [[lophophore]]-like organ || none
|- align="center"
! Colonial
| Colonies of clones in most; one solitary [[genus]] || colspan="3" | [[Sessility (zoology)|Sessile]] species often form clumps, but with no active co-operation || Colonies of clones in some species; some solitary species || Colonies of clones
|- align="center"
! Shape of founder zooid
| Round, unlike normal zooids<ref name="RichFenton1997Bryozoans" /> || colspan="3" | not applicable || colspan="2" | Same as other zooids
|- align="center"
! [[Biomineralization|Mineralized]] [[exoskeleton]]s
| Some [[taxon|taxa]] || no || [[Bivalve]]-like shells || Some sessile annelids build mineralized tubes;<ref name="RuppertFoxBarnesAnnelGen">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Annelida | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/414 414–420] | chapter-url=https://archive.org/details/isbn_9780030259821/page/414 }}</ref> most molluscs have shells, but most modern [[cephalopod]]s have internal shells or none.<ref name="RuppertFoxBarnes2004MolluscaGen">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/284 284–291] | url=https://archive.org/details/isbn_9780030259821/page/284 }}</ref> || no || Some taxa
|}

=== Types of zooid ===
All bryozoans are colonial except for one [[genus]], ''[[Monobryozoon]]''.<ref>{{cite book|last=Giere|first=O.|title=Meiobenthology|publisher=Springer Verlag|year=2009|edition=2nd|page=227|chapter=Tentaculata|isbn=978-3-540-68657-6|chapter-url=https://books.google.com/books?id=an9ncYOxkUoC&q=solitary+bryozoan&pg=PA227|access-date=2009-07-07|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183240/https://books.google.com/books?id=an9ncYOxkUoC&q=solitary+bryozoan&pg=PA227|url-status=live}}</ref><ref name="Doherty2001EctoproctaInAnderson">{{cite book
| author=Doherty, P.J. | year=2001| edition=2nd| chapter=The Lophophorates | pages=363–373
| editor=Anderson, D.T.| title=Invertebrate Zoology| publisher=Oxford University Press
| isbn=978-0-19-551368-4
}}</ref> Individual members of a bryozoan colony are about {{cvt|0.5|mm|in|frac=64}} long and are known as ''zooids'',<ref name="RuppertFoxBarnesBryozoa">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Lophoporata | publisher=Brooks / Cole | edition=7th | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/829 829–845] | chapter-url=https://archive.org/details/isbn_9780030259821/page/829 }}</ref> since they are not fully independent animals.<ref>{{cite book|last=Little|first=W.|author2=Fowler, H.W |author3=Coulson, J. |author4=Onions, C.T. |name-list-style=amp |title=Shorter Oxford English Dictionary|publisher=Oxford University Press|year=1964|chapter=Zooid|isbn=978-0-19-860613-0}}</ref> All colonies contain feeding zooids, known as autozooids. Those of some groups also contain non-feeding heterozooids, also known as polymorphic zooids, which serve a variety of functions other than feeding;<ref name="Doherty2001EctoproctaInAnderson" /> colony members are genetically identical and co-operate, rather like the organs of larger animals.<ref name="RuppertFoxBarnesBryozoa" /> What type of zooid grows where in a colony is determined by chemical signals from the colony as a whole or sometimes in response to the scent of predators or rival colonies.<ref name="Doherty2001EctoproctaInAnderson" />

The bodies of all types have two main parts. The ''cystid'' consists of the body wall and whatever type of [[exoskeleton]] is [[secretion|secreted]] by the [[Epidermis (zoology)|epidermis]]. The exoskeleton may be organic ([[chitin]], [[polysaccharide]] or [[protein]]) or made of the mineral [[calcium carbonate]]. The latter is always absent in freshwater species.<ref>[http://palaeontologicalsociety.in/vol50_2/v1.pdf Bryozoans and Palaeoenvironmental Interpretation]</ref> The body wall consists of the epidermis, [[basal lamina]] (a mat of non-cellular material), [[connective tissue]], muscles, and the [[mesothelium]] which lines the [[coelom]] (main body cavity)<ref name="RuppertFoxBarnesBryozoa" /> – except that in one class, the mesothelium is split into two separate layers, the inner one forming a membranous sac that floats freely and contains the coelom, and the outer one attached to the body wall and enclosing the membranous sac in a [[pseudocoelom]].<ref name="Nielsen2001InEncOfLifeSci">{{cite book
| contribution=Bryozoa (Ectoprocta: 'Moss' Animals) | author=Nielsen, C.
| title=Encyclopedia of Life Sciences | year=2001 | publisher= John Wiley & Sons, Ltd. | doi=10.1038/npg.els.0001613
| isbn=978-0470016176
}}</ref> The other main part of the bryozoan body, known as the ''polypide'' and situated almost entirely within the cystid, contains the nervous system, digestive system, some specialized muscles and the feeding apparatus or other specialized organs that take the place of the feeding apparatus.<ref name="RuppertFoxBarnesBryozoa" />

==== Feeding zooids ====
{{Annotated image | align=right | caption=A generalized autozooid<ref name="RuppertFoxBarnesBryozoa" />
| image=Ectoproct generalized 01.png
| width=280 | height=400 | image-width=156 | image-left=52
|annotations=
{{Annotation|30|108|[[Pharynx]]}}
{{Annotation|30|128|Invert}}
{{Annotation|15|160|Retractor muscle}}
{{Annotation|30|205|[[Ovary]]}}
{{Annotation|15|243|Protective covering}}
{{Annotation|200|20|Lophophore's tentacles}}
{{Annotation|180|98|[[Ganglion]]}}
{{Annotation|180|118|[[Anus]]}}
{{Annotation|195|188|[[Coelom]] (body cavity)}}
{{Annotation|195|228|Stomach }}
{{Annotation|195|262|[[Testis]] }}
{{Annotation|195|280|Funiculus }}
{{Annotation|15|330|{{legend2|border=solid 1px silver|yellow|{{=}} [[Digestive tract]]}}}}
{{Annotation|160|330|{{legend2|border=solid 1px silver|lime|{{=}} [[Gonad]]s}}}}
{{Annotation|15|370|{{legend2|border=solid 1px silver|#a500a5|{{=}} Retractor muscle}}}}
{{Annotation|160|370|{{legend2|border=solid 1px silver|#808000|{{=}} Outer covering}}}}
}}
The most common type of zooid is the feeding autozooid, in which the polypide bears a "crown" of hollow tentacles called a [[lophophore]], which captures food particles from the water.<ref name="Doherty2001EctoproctaInAnderson" /> In all colonies a large percentage of zooids are autozooids, and some consist entirely of autozooids, some of which also engage in reproduction.<ref name="McKinneyJackson">{{cite book|last=McKinney|first=F.K.|author2=Jackson, J.B.C.|title=Bryozoan evolution|publisher=University of Chicago Press|year=1991|pages=1–13|chapter=Bryozoans as modular machines|isbn=978-0-226-56047-2|chapter-url=https://books.google.com/books?id=TMnsG36wHoIC&q=Avicularia+bryozoa&pg=PA7|access-date=2009-07-29|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183241/https://books.google.com/books?id=TMnsG36wHoIC&q=Avicularia+bryozoa&pg=PA7|url-status=live}}</ref>

The basic shape of the "crown" is a full circle. Among the [[Phylactolaemata|freshwater bryozoans]] ([[Phylactolaemata]]) the crown appears U-shaped, but this impression is created by a deep dent in the rim of the crown, which has no gap in the fringe of tentacles.<ref name="RuppertFoxBarnesBryozoa" /> The sides of the tentacles bear fine hairs called [[cilia]], whose beating drives a water current from the tips of the tentacles to their bases, where it exits. Food particles that collide with the tentacles are trapped by [[mucus]], and further cilia on the inner surfaces of the tentacles move the particles towards the mouth in the center.<ref name="RuppertFoxBarnesLophophorataGen"/> The method used by ectoprocts is called "upstream collecting", as food particles are captured before they pass through the field of cilia that creates the feeding current. This method is also used by [[phoronid]]s, [[brachiopod]]s and [[pterobranch]]s.<ref>{{cite journal|last1=Riisgård|first1=H.U.|year=2000|title=Downstream collecting in ciliary suspension feeders: the catch-up principle|journal=Marine Ecology Progress Series|volume=207|pages=33–51|url=https://www.int-res.com/articles/meps/207/m207p033.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.int-res.com/articles/meps/207/m207p033.pdf |archive-date=2022-10-09 |url-status=live|access-date=12 September 2009|doi=10.3354/meps207033|last2=Nielsen|first2=C|last3=Larsen|first3=PS|bibcode=2000MEPS..207...33R|doi-access=free}}</ref>

The lophophore and mouth are mounted on a flexible tube called the "invert", which can be turned inside-out and withdrawn into the polypide,<ref name="RuppertFoxBarnesBryozoa" /> rather like the finger of a rubber glove; in this position the lophophore lies inside the invert and is folded like the spokes of an umbrella. The invert is withdrawn, sometimes within 60{{nbsp}}[[millisecond]]s, by a pair of retractor muscles that are anchored at the far end of the cystid. Sensors at the tips of the tentacles may check for signs of danger before the invert and lophophore are fully extended. Extension is driven by an increase in internal fluid pressure, which species with flexible exoskeletons produce by contracting circular muscles that lie just inside the body wall,<ref name="RuppertFoxBarnesBryozoa" /> while species with a membranous sac use circular muscles to squeeze this.<ref name="Nielsen2001InEncOfLifeSci" /> Some species with rigid exoskeletons have a flexible membrane that replaces part of the exoskeleton, and transverse muscles anchored on the far side of the exoskeleton increase the fluid pressure by pulling the membrane inwards.<ref name="RuppertFoxBarnesBryozoa" /> In others there is no gap in the protective skeleton, and the transverse muscles pull on a flexible sac which is connected to the water outside by a small pore; the expansion of the sac increases the pressure inside the body and pushes the invert and lophophore out.<ref name="RuppertFoxBarnesBryozoa" /> In some species the retracted invert and lophophore are protected by an operculum ("lid"), which is closed by muscles and opened by fluid pressure. In one [[class (biology)|class]], a hollow lobe called the "epistome" overhangs the mouth.<ref name="RuppertFoxBarnesBryozoa" />

The gut is U-shaped, running from the mouth, in the center of the lophophore, down into the animal's interior and then back to the [[anus]], which is located on the invert, outside and usually below the lophophore.<ref name="RuppertFoxBarnesBryozoa" /> A network of strands of [[mesothelium]] called "funiculi" ("little ropes")<ref name="RanHouDictFuniculus">{{cite book|title=Random House Dictionary|publisher=Random House|chapter=funiculus|chapter-url=http://dictionary.reference.com/browse/funiculus|access-date=2009-08-02|archive-date=13 May 2010|archive-url=https://web.archive.org/web/20100513073724/http://dictionary.reference.com/browse/funiculus|url-status=live}}</ref> connects the mesothelium covering the gut with that lining the body wall. The wall of each strand is made of mesothelium, and surrounds a space filled with fluid, thought to be blood.<ref name="RuppertFoxBarnesBryozoa" /> A colony's zooids are connected, enabling autozooids to share food with each other and with any non-feeding heterozooids.<ref name="RuppertFoxBarnesBryozoa" /> The method of connection varies between the different classes of bryozoans, ranging from quite large gaps in the body walls to small pores through which nutrients are passed by funiculi.<ref name="RuppertFoxBarnesBryozoa" /><ref name="Nielsen2001InEncOfLifeSci" />

There is a nerve ring round the pharynx (throat) and a [[ganglion]] that serves as a brain to one side of this. Nerves run from the ring and ganglion to the tentacles and to the rest of the body.<ref name="RuppertFoxBarnesBryozoa" /> Bryozoans have no specialized sense organs, but [[cilia]] on the tentacles act as sensors. Members of the [[genus]] ''[[Bugula]]'' [[phototropism|grow towards the sun]], and therefore must be able to detect light.<ref name="RuppertFoxBarnesBryozoa" /> In colonies of some species, signals are transmitted between zooids through nerves that pass through pores in the body walls, and coordinate activities such as feeding and the retraction of lophophores.<ref name="RuppertFoxBarnesBryozoa" />

The solitary individuals of ''Monobryozoon'' are autozooids with pear-shaped bodies. The wider ends have up to 15 short, muscular projections by which the animals anchor themselves to sand or gravel<ref>{{cite book|last=Hayward|first=P.J.|title=Ctenostome Bryozoans|publisher=Linnean Society of London|year=1985|series=Synopses of the British fauna|pages=106–107|chapter=Systematic part|isbn=978-90-04-07583-2|chapter-url=https://books.google.com/books?id=HgwVAAAAIAAJ&q=monobryozoon&pg=PA106|access-date=2009-08-02|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183239/https://books.google.com/books?id=HgwVAAAAIAAJ&q=monobryozoon&pg=PA106|url-status=live}}</ref> and pull themselves through the sediments.<ref>{{cite book|last=Giere|first=O.|title=Meiobenthology|publisher=Springer-Verlag|year=2009|edition=2nd|page=227|chapter=Tentaculata|isbn=978-3-540-68657-6|chapter-url=https://books.google.com/books?id=an9ncYOxkUoC&q=monobryozoon&pg=PA227|access-date=2009-08-02|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183241/https://books.google.com/books?id=an9ncYOxkUoC&q=monobryozoon&pg=PA227|url-status=live}}</ref>

==== Avicularia and vibracula ====
Some authorities use the term ''avicularia'' (plural of ''[[avicularium]]'') to refer to any type of zooid in which the lophophore is replaced by an extension that serves some protective function,<ref name="McKinneyJackson" /> while others restrict the term to those that defend the colony by snapping at invaders and small predators, killing some and biting the [[appendage]]s of others.<ref name="RuppertFoxBarnesBryozoa" /> In some species the snapping zooids are mounted on a peduncle (stalk), their bird-like appearance responsible for the term – [[Charles Darwin]] described these as like "the head and beak of a vulture in miniature, seated on a neck and capable of movement".<ref name="RuppertFoxBarnesBryozoa" /><ref name="McKinneyJackson" /> Stalked avicularia are placed upside-down on their stalks.<ref name="Doherty2001EctoproctaInAnderson" /> The "lower jaws" are modified versions of the opercula that protect the retracted lophophores in autozooids of some species, and are snapped shut "like a mousetrap" by similar muscles,<ref name="RuppertFoxBarnesBryozoa" /> while the beak-shaped upper jaw is the inverted body wall.<ref name="Doherty2001EctoproctaInAnderson" /> In other species the avicularia are stationary box-like zooids laid the normal way up, so that the modified operculum snaps down against the body wall.<ref name="Doherty2001EctoproctaInAnderson" /> In both types the modified operculum is opened by other muscles that attach to it,<ref name="McKinneyJackson" /> or by internal muscles that raise the fluid pressure by pulling on a flexible membrane.<ref name="RuppertFoxBarnesBryozoa" /> The actions of these snapping zooids are controlled by small, highly modified polypides that are located inside the "mouth" and bear tufts of short sensory [[cilia]].<ref name="RuppertFoxBarnesBryozoa" /><ref name="Doherty2001EctoproctaInAnderson" /> These zooids appear in various positions: some take the place of autozooids, some fit into small gaps between autozooids, and small avicularia may occur on the surfaces of other zooids.<ref name="McKinneyJackson" />

In vibracula, regarded by some as a type of avicularia, the operculum is modified to form a long bristle that has a wide range of motion. They may function as defenses against predators and invaders, or as cleaners. In some species that form mobile colonies, vibracula around the edges are used as legs for burrowing and walking.<ref name="RuppertFoxBarnesBryozoa" /><ref name="McKinneyJackson" />

==== Structural polymorphs ====
Kenozooids (from the Greek {{grc-transl|κενός}} 'empty')<ref>{{cite book|last=Liddell|first=H.G.|author2=Scott R.|title=A Greek-English Lexicon|publisher=Clarendon Press|year=1940|chapter=kenos|isbn=978-0-19-864226-8|chapter-url=https://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%2356587|access-date=2009-08-01|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183237/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%2356587&redirect=true|url-status=live}}</ref> consist only of the body wall and funicular strands crossing the interior,<ref name="RuppertFoxBarnesBryozoa" /> and no polypide.<ref name="Doherty2001EctoproctaInAnderson" /> The functions of these zooids include forming the stems of branching structures, acting as spacers that enable colonies to grow quickly in a new direction,<ref name="Doherty2001EctoproctaInAnderson" /><ref name="McKinneyJackson" /> strengthening the colony's branches, and elevating the colony slightly above its substrate for competitive advantages against other organisms. Some kenozooids are hypothesized to be capable of storing nutrients for the colony.{{Sfn|Taylor|2020|pp=72–73}} Because kenozooids' function is generally structural, they are called "structural polymorphs."

Some heterozooids found in extinct trepostome bryozoans, called mesozooids, are thought to have functioned to space the feeding autozooids an appropriate distance apart. In thin sections of trepostome fossils, mesozooids can be seen in between the tubes that held autozooids; they are smaller tubes that are divided along their length by diaphragms, making them look like rows of box-like chambers sandwiched between autozooidal tubes.{{Sfn|Taylor|2020|p=74}}

==== Reproductive polymorphs ====
Gonozooids act as brood chambers for fertilized eggs.<ref name="Doherty2001EctoproctaInAnderson" /> Almost all modern cyclostome bryozoans have them, but they can be hard to locate on a colony because there are so few gonozooids in one colony. The aperture in gonozooids, which is called an ooeciopore, acts as a point for larvae to exit. Some gonozooids have very complex shapes with autozooidal tubes passing through chambers within them. All larvae released from a gonozooid are clones created by division of a single egg; this is called monozygotic [[polyembryony]], and is a reproductive strategy also used by [[armadillo]]s.{{Sfn|Taylor|2020|p=59}}

Cheilostome bryozoans also brood their embryos; one of the common methods is through ovicells, capsules attached to autozooids. The autozooids possessing ovicells are normally still able to feed, however, so these are not considered heterozooids.{{Sfn|Taylor|2020|p=60}}

"Female" polymorphs are more common than "male" polymorphs, but specialized zooids that produce sperm are also known. These are called androzooids, and some are found in colonies of ''Odontoporella bishopi'', a species that is [[Symbiosis|symbiotic]] with [[hermit crab]]s and lives on their shells. These zooids are smaller than the others and have four short tentacles and four long tentacles, unlike the autozooids which have 15–16 tentacles. Androzooids are also found in species with mobile colonies that can crawl around. It is possible that androzooids are used to exchange sperm between colonies when two mobile colonies or bryozoan-encrusted hermit crabs happen to encounter one another.{{Sfn|Taylor|2020|p=65}}

====Other polymorphs====
Spinozooids are hollow, movable spines, like very slender, small tubes, present on the surface of colonies, which probably are for defense.{{Sfn|Taylor|2020|p=75}} Some species have miniature nanozooids with small single-tentacled polypides, and these may grow on other zooids or within the body walls of autozooids that have degenerated.<ref name="McKinneyJackson" />

=== Colony forms and composition ===
[[File:Flustra foliacea.jpg|thumb|A colony of the modern marine bryozoan ''Flustra foliacea''.]]
[[File:Cheilostome Serpulid Cape Cod.JPG|thumb|Cheilostome bryozoan with serpulid tubes]]

Although zooids are microscopic, colonies range in size from {{cvt|1|cm|in|frac=4}} to over {{cvt|1|m|ftin}}.<ref name="RuppertFoxBarnesBryozoa" /> However, the majority are under {{cvt|10|cm|in|0}} across.<ref name="RichFenton1997Bryozoans">{{cite book|last=Rich|first=T.H.|author2=Fenton, M.A.|author3=Fenton, C.L.|title=The fossil book|publisher=Dover Publications|year=1997|pages=[https://archive.org/details/fossilbookrecor00rich/page/142 142–152]|chapter='Moss Animals', or Bryozoans|isbn=978-0-486-29371-4|chapter-url=https://books.google.com/books?id=_ntSspji0LYC&q=bryozoans&pg=PA141|access-date=2009-08-07|url=https://archive.org/details/fossilbookrecor00rich/page/142}}</ref> The shapes of colonies vary widely, depend on the pattern of budding by which they grow, the variety of zooids present and the type and amount of skeletal material they [[secretion|secrete]].<ref name="RuppertFoxBarnesBryozoa" />

Some marine species are bush-like or fan-like, supported by "trunks" and "branches" formed by kenozooids, with feeding autozooids growing from these. Colonies of these types are generally [[biomineralization|unmineralized]] but may have [[exoskeleton]]s made of [[chitin]].<ref name="RuppertFoxBarnesBryozoa" /> Others look like small [[coral]]s, producing heavy lime skeletons.<ref>{{cite book|last=Branch|first=M.L.|author2=Griffiths, C.I.|author3=Beckley, L.E.|title=Two Oceans – A Guide to the Marine Life of Southern Africa|publisher=Struik|year=2007|pages=104–110|chapter=Bryozoa: Moss or Lace Animals|isbn=978-1-77007-633-4|chapter-url=https://books.google.com/books?id=W_2QB8ftLgcC&q=bryozoa+lace+animal&pg=PA104|access-date=2009-08-02}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Many species form colonies which consist of sheets of autozooids. These sheets may form leaves, tufts or, in the [[genus]] ''[[Thalamoporella]]'', structures that resemble an open head of lettuce.<ref name="RuppertFoxBarnesBryozoa" />

The most common marine form, however, is encrusting, in which a one-layer sheet of zooids spreads over a hard surface or over seaweed. Some encrusting colonies may grow to over {{cvt|50|cm|ftin|0}} and contain about 2,000,000 zooids.<ref name="RuppertFoxBarnesBryozoa" /> These species generally have exoskeletons reinforced with [[calcium carbonate]], and the openings through which the lophophores protrude are on the top or outer surface.<ref name="RuppertFoxBarnesBryozoa" /> The moss-like appearance of encrusting colonies is responsible for the phylum's name ([[Ancient Greek]] words {{lang|grc|βρύον}} {{grc-tr|βρύον}} meaning 'moss' and {{lang|grc|ζῷον}} {{grc-tr|ζῷον}} meaning 'animal').<ref name="SOED1959Bryozoa">{{cite book|last=Little|first=W.|author2=Fowler, H.W. |author3=Coulson, J. |author4=Onions, C.T. |name-list-style=amp |title=Shorter Oxford English Dictionary|publisher=Oxford University|year=1959|chapter=Bryozoa|isbn=978-0-19-860613-0}}</ref> Large colonies of encrusting species often have "[[chimney]]s", gaps in the canopy of lophophores, through which they swiftly expel water that has been sieved, and thus avoid re-filtering water that is already exhausted.<ref>{{cite journal|last1=Eckman|first1=J.E.|date=December 1998|title=A Model of Particle Capture by Bryozoans in Turbulent Flow: Significance of Colony Form|volume=152|pages=861–880 | doi=10.1086/286214|journal=The American Naturalist|pmid=18811433|last2=Okamura|first2=B|issue=6|bibcode=1998ANat..152..861E |s2cid=5535013}}</ref> They are formed by patches of non-feeding heterozooids.<ref>{{cite book|last=Vogel|first=S.|title=Life in moving fluids|publisher=Princeton University Press|year=1996|edition=2nd|page=191|chapter=Life in velocity gradients|isbn=978-0-691-02616-9|chapter-url=https://books.google.com/books?id=XBqncfXFsOIC&q=bryozoan+chimney&pg=PA191|access-date=2009-08-05|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183243/https://books.google.com/books?id=XBqncfXFsOIC&q=bryozoan+chimney&pg=PA191|url-status=live}}</ref> New chimneys appear near the edges of expanding colonies, at points where the speed of the outflow is already high, and do not change position if the water flow changes.<ref>{{cite journal|last=von Dassow|first=M.|title=Function-Dependent Development in a Colonial Animal|journal=Biological Bulletin|volume=211|pages=76–82|url=http://www.biolbull.org/cgi/content/full/211/1/76|access-date=2009-08-05|doi=10.2307/4134580|issn=0006-3185|date=1 August 2006|issue=1|pmid=16946244|jstor=4134580|archive-url=https://web.archive.org/web/20090706012640/http://www.biolbull.org/cgi/content/full/211/1/76|archive-date=6 July 2009|url-status=dead}}</ref>

Some freshwater species secrete a mass of gelatinous material, up to {{cvt|1|m|ftin}} in diameter, to which the zooids stick. Other freshwater species have plant-like shapes with "trunks" and "branches", which may stand erect or spread over the surface. A few species can creep at about {{cvt|2|cm|in|frac=4}} per day.<ref name="RuppertFoxBarnesBryozoa" />

Each colony grows by [[asexual reproduction|asexual]] [[budding]] from a single zooid known as the ancestrula,<ref name="RuppertFoxBarnesBryozoa" /> which is round rather than shaped like a normal zooid.<ref name="RichFenton1997Bryozoans" /> This occurs at the tips of "trunks" or "branches" in forms that have this structure. Encrusting colonies grow round their edges. In species with [[calcareous]] exoskeletons, these do not mineralize until the zooids are fully grown. Colony lifespans range from one to about 12 years, and the short-lived species pass through several generations in one season.<ref name="RuppertFoxBarnesBryozoa" />

Species that produce defensive zooids do so only when threats have already appeared, and may do so within 48 hours.<ref name="Doherty2001EctoproctaInAnderson" /> The theory of "induced defenses" suggests that production of defenses is expensive and that colonies which defend themselves too early or too heavily will have reduced growth rates and lifespans. This "last minute" approach to defense is feasible because the loss of zooids to a single attack is unlikely to be significant.<ref name="Doherty2001EctoproctaInAnderson" /> Colonies of some encrusting species also produce special heterozooids to limit the expansion of other encrusting organisms, especially other bryozoans. In some cases this response is more belligerent if the opposition is smaller, which suggests that zooids on the edge of a colony can somehow sense the size of the opponent. Some species consistently prevail against certain others, but most [[wikt:turf war|turf war]]s are indecisive and the combatants soon turn to growing in uncontested areas.<ref name="Doherty2001EctoproctaInAnderson" /> Bryozoans competing for territory do not use the sophisticated techniques employed by [[sponge]]s or [[coral]]s, possibly because the shortness of bryozoan lifespans makes heavy investment in turf wars unprofitable.<ref name="Doherty2001EctoproctaInAnderson" />

Bryozoans have contributed to carbonate sedimentation in marine life since the Ordovician period. Bryozoans take responsibility for many of the colony forms, which have evolved in different taxonomic groups and vary in sediment producing ability. The nine basic bryozoan colony-forms include: encrusting, dome-shaped, palmate, foliose, fenestrate, robust branching, delicate branching, articulated and free-living. Most of these sediments come from two distinct groups of colonies: domal, delicate branching, robust branching and palmate; and fenestrate. Fenestrate colonies generate rough particles both as sediment and components of stromatoporoids coral reefs. The delicate colonies however, create both coarse sediment and form the cores of deep-water, subphotic biogenic mounds. Nearly all post- bryozoan sediments are made up of growth forms, with the addition to free-living colonies which include significant numbers of various colonies. "In contrast to the Palaeozoic, post-Palaeozoic bryozoans generated sediment varying more widely with the size of their grains; they grow as they moved from mud, to sand, to gravel."<ref>{{cite journal|last1=Taylor|first1=Paul D.|last2=James|first2=Noel P.|title=Secular changes in colony-forms and bryozoan carbonate sediments through geological history|journal=Sedimentology|date=August 2013|volume=60|issue=5|pages=1184–1212|doi=10.1111/sed.12032|s2cid=128939236 |doi-access=free}}</ref>

== Taxonomy ==
{{See also|List of bilaterial animal orders}}
[[File:Peronopora080512.JPG|thumb|''Peronopora'', a trepostome bryozoan from the Whitewater Formation (Upper [[Ordovician]]) of eastern [[Indiana]], United States]]
[[File:The Childrens Museum of Indianapolis - Evactinopora bryozoan - detail.jpg|thumb|''Evactinopora'' bryozoan found in Jefferson County, [[Missouri]], United States]]

The phylum was originally called "Polyzoa", but this name was eventually replaced by Ehrenberg's term "Bryozoa".<ref name="Muir-Wood 1955"/><ref name="BeattyBlackwelder1974" /><ref name="Mayr1968BryozoaVersusEctoprocta" /> The name "Bryozoa" was originally applied only to the animals also known as Ectoprocta ({{lit|outside-anus}}),<ref>{{cite book |last=Little |first=W. |author2=Fowler, H.W |author3=Coulson, J. |author4=Onions, C.T. |name-list-style=amp |title=Shorter Oxford English Dictionary |publisher=Oxford University Press |year=1964 |chapter=Ecto- |isbn=978-0-19-860613-0}}</ref> in which the [[anus]] lies outside the "crown" of tentacles. After the discovery of the [[Entoprocta]] ({{lit|inside-anus}}),<ref>{{cite book |last=Little |first=W. |author2=Fowler, H.W. |author3=Coulson, J. |author4=Onions, C.T. |name-list-style=amp |title=Shorter Oxford English Dictionary |publisher=Oxford University Press |year=1964 |chapter=Ento- |isbn=978-0-19-860613-0}}</ref> in which the anus lies within a "crown" of tentacles, the name "Bryozoa" was promoted to [[phylum]] level to include the two [[class (biology)|classes]] Ectoprocta and Entoprocta.<ref name="Halanych2004AnimalPhylogeny">{{cite journal |last=Halanych |first=K.M. |year=2004 |title=The new view of animal phylogeny |journal=Annual Review of Ecology, Evolution, and Systematics |volume=35 |pages=229–256 |url=http://www-fourier.ujf-grenoble.fr/~dpiau/cdem/130124b.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www-fourier.ujf-grenoble.fr/~dpiau/cdem/130124b.pdf |archive-date=2022-10-09 |url-status=live |access-date=2016-08-26 | doi=10.1146/annurev.ecolsys.35.112202.130124}}</ref> However, in 1869 Hinrich Nitsche regarded the two groups as quite distinct for a variety of reasons, and coined the name "Ectoprocta" for Ehrenberg's "Bryozoa".<ref name="FuchsObstSundberg2009ComprMolPhyloOfBryozoa" /><ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics" /> Despite their apparently similar methods of feeding, they differed markedly anatomically; in addition to the different positions of the anus, ectoprocts have hollow tentacles and a [[coelom]], while entoprocts have solid tentacles and no coelom. Hence the two groups are now widely regarded as separate phyla, and the name "Bryozoa" is now synonymous with "Ectoprocta".<ref name="Halanych2004AnimalPhylogeny" /> This has remained the majority view ever since, although most publications have preferred the name "Bryozoa" rather than "Ectoprocta".<ref name="Mayr1968BryozoaVersusEctoprocta">{{cite journal |last=Mayr |first=E. |date=June 1968 |title=Bryozoa versus Ectoprocta |journal=Systematic Zoology |volume=17 |issue=2 |pages=213–216 |jstor=2412368 |doi=10.2307/2412368}}</ref> Nevertheless, some notable scientists have continued to regard the "Ectoprocta" and Entoprocta as close relatives and group them under "Bryozoa".<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics"/>

The ambiguity about the scope of the name "Bryozoa" led to proposals in the 1960s and 1970s that it should be avoided and the unambiguous term "Ectoprocta" should be used.<ref>{{cite journal |last=Cuffey |first=R. J. |year=1969 |title=Bryozoa versus Ectoprocta – The Necessity for Precision |journal=Systematic Zoology |volume=18 |issue=2 |pages=250–251 |doi=10.2307/2412617 |jstor=2412617 }}</ref> However, the change would have made it harder to find older works in which the phylum was called "Bryozoa", and the desire to avoid ambiguity, if applied consistently to all classifications, would have necessitated renaming of several other phyla and many lower-level groups.<ref name="BeattyBlackwelder1974">{{cite journal |last=Beatty |first=J.A. |year=1974 |title=Names of Invertebrate Phyla |journal=Systematic Zoology |volume=23 |issue=4 |pages=545–547 |jstor=2412472 |doi=10.2307/2412472 |author2=Blackwelder}}</ref> In practice, zoological naming of split or merged groups of animals is complex and not completely consistent.<ref>{{cite journal |last=Ghiselin |first=M.T. |year=1977 |title=On Changing the Names of Higher Taxa |journal=Systematic Zoology |volume=26 |issue=3 |pages=346–349 |jstor=2412681 |doi=10.2307/2412681}}</ref> Works since 2000 have used various names to resolve the ambiguity, including: "Bryozoa",<ref name="RuppertFoxBarnesBryozoa" /><ref name="RichFenton1997Bryozoans" /> "Ectoprocta",<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /><ref name="Doherty2001EctoproctaInAnderson" /> "Bryozoa (Ectoprocta)",<ref name="Nielsen2001InEncOfLifeSci" /> and "Ectoprocta (Bryozoa)".<ref>{{cite journal |last1=Yokobori |first1=S. |date=May 2008 |title=Complete nucleotide sequences of mitochondrial genomes of two solitary entoprocts, ''Loxocorone allax'' and ''Loxosomella aloxiata'': Implications for lophotrochozoan phylogeny |journal=Molecular Phylogenetics and Evolution |volume=47 |issue=2 |pages=612–628 |doi=10.1016/j.ympev.2008.02.013 |pmid=18374604 |last2=Iseto |first2=T |last3=Asakawa |first3=S |last4=Sasaki |first4=T |last5=Shimizu |first5=N |last6=Yamagishi |first6=A |last7=Oshima |first7=T |last8=Hirose |first8=E|bibcode=2008MolPE..47..612Y }}</ref> Some have used more than one approach in the same work.<ref>{{cite journal |last=Reynolds |first=K.T. |year=2000 |title=Taxonomically Important Features on the Surface of Floatoblasts in ''Plumatella'' (Bryozoa) |journal=Microscopy and Microanalysis |volume=6 |issue=3 |pages=202–210 |pmid= 10790488 |doi=10.1017/S1431927600000349 |bibcode=2000MiMic...6..202R}} The text begins "Phylum Ectoprocta (Bryozoa) ..."</ref>

The common name "moss animals" is the literal meaning of "Bryozoa", from Greek {{lang|grc|βρυόν}} ('moss') and {{lang|grc|ζῷα}} ('animals'), based on the mossy appearance of encrusting species.<ref>{{cite book | last1=Trumble | first1=W | author2=Brown, L | title=Shorter Oxford English Dictionary | chapter-url=https://archive.org/details/shorteroxfordeng00will_0 | chapter-url-access=registration | publisher=Oxford University Press | year=2002 | isbn=978-0-19-860457-0 | chapter=Bryozoa }}</ref>
<!--[[ITIS]], the Integrated Taxonomic Information System, designates the phylum as "Ectoprocta",<ref name="ITISEctoprocta">{{cite web |url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=155470 |title=ITIS Standard Report Page: Ectoprocta |publisher=[[Integrated Taxonomic Information System]] |access-date=2009-08-23}}</ref> referring to the position of the [[anus]] outside the "crown" of feeding tentacles (based on the [[Ancient Greek]] prefix {{lang|grc|ἐκτο}} meaning "outside" and word {{lang|grc|πρωκτος}} meaning "anus").<ref>{{cite book |last=Little |first=W. |author2=Fowler, H.W, Coulson, J. and Onions, C.T. |title=Shorter Oxford English Dictionary |publisher=Oxford University Press |date=1964 |chapter=Ecto- |isbn=0-19-860613-3}}</ref> The term "Bryozoa" (from the Ancient Greek words {{lang-grc|βρυος|bryos|label=none}} meaning "moss" and {{lang-grc|ζωον|zoon|label=none}} meaning "animal") is widely used to refer to Ectoprocta in books and articles.<ref name="Nielsen2002PhyloPosOfEntoproctaEctoproctaPhoronidaBrachiopoda" /> because some species look moss-like.<ref name="SOED1959Bryozoa" /> However, the name "Bryozoa" has also been used for the combination of Ectoprocta with [[Entoprocta]], which are distinguished by having the anus inside a "crown" of tentacles (based on the Ancient Greek prefix {{lang|grc|ἐντο}} meaning "inside" and word {{lang|grc|πρωκτος}} meaning "anus"),<ref>{{cite book |last=Little |first=W. |author2=Fowler, H.W, Coulson, J. and Onions, C.T. |title=Shorter Oxford English Dictionary |publisher=Oxford University Press |date=1964 |chapter=Ento- |isbn=0-19-860613-3}}</ref> and the differing meanings of "Bryozoa" have caused much confusion.<ref>{{cite journal |last=Cuffey |first=R. J. |date=1969 |title=Bryozoa versus Ectoprocta – The Necessity for Precision |journal=Systematic Zoology |volume=18 |issue=2 |pages=250–251 |doi=10.2307/2412617 |jstor=2412617 }}</ref> ITIS treats the term "Bryozoa" as "invalid – junior synonym", in other words "Ectoprocta" is the longer-established name and ITIS recommends that "Bryozoa" should not be used to identify this phylum.<ref>{{cite web |url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=155469 |title=ITIS Standard Report Page: Bryozoa |publisher=Integrated Taxonomic Information System |access-date=2009-08-23}}</ref> -->

Until 2008 there were "inadequately known and misunderstood type species belonging to the Cyclostome Bryozoan family Oncousoeciidae."<ref>Taylor, Zaton 2008</ref> Modern research and experiments have been done using low-vacuum scanning electron microscopy of uncoated type material to critically examine and perhaps revise the taxonomy of three genera belonging to this family, including ''Oncousoecia'', ''Microeciella'', and ''Eurystrotos''. This method permits data to be obtained that would be difficult to recognize with an optical microscope. The valid type species of ''Oncousoecia'' was found to be ''Oncousoecia lobulata''. This interpretation stabilizes ''Oncousoecia'' by establishing a type species that corresponds to the general usage of the genus. Fellow Oncousoeciid ''Eurystrotos'' is now believed to be not conspecific with ''O. lobulata'', as previously suggested, but shows enough similarities to be considered a junior synonym of ''Oncousoecia''. ''Microeciella suborbicularus'' has also been recently distinguished from ''O. lobulata'' and ''O. dilatans'', using this modern method of low vacuum scanning, with which it has been inaccurately synonymized with in the past. A new genus has also been recently discovered called ''Junerossia'' in the family Stomachetosellidae, along with 10 relatively new species of bryozoa such as ''Alderina flaventa'', ''Corbulella extenuata'', ''Puellina septemcryptica'', ''Junerossia copiosa'', ''Calyptotheca kapaaensis'', ''Bryopesanser serratus'', ''Cribellopora souleorum'', ''Metacleidochasma verrucosa'', ''Disporella compta'', and ''Favosipora adunca''.<ref>{{cite journal |last1=Taylor |first1=Paul D |title=Taxonomy of the bryozoan genera Oncousoecia, Microeciella and Eurystrotos |journal=Journal of Natural History |date=October 2008 |volume= 42 |issue=39–40 |pages=2557–2574 |doi=10.1080/00222930802277640 |s2cid=84315311}}</ref>

=== Classification and diversity ===
Counts of formally described species range between 4,000 and 4,500.<ref>{{cite book |last=Chapman |first=A.D. |title=Numbers of Living Species in Australia and the World |publisher=Department of the Environment and Heritage, Australian Government |year=2006 |page=34 |isbn=978-0-642-56849-6 |url=http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/pubs/number-living-species-report.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/pubs/number-living-species-report.pdf |archive-date=2022-10-09 |url-status=live |access-date=2009-08-07}}</ref> The Gymnolaemata and especially Cheilostomata have the greatest numbers of species, possibly because of their wide range of specialist zooids.<ref name="Doherty2001EctoproctaInAnderson" /> Under the [[Linnaean taxonomy|Linnaean system of classification]], which is still used as a convenient way to label groups of organisms,<ref name="RuppertFoxBarnesCladistics">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp | title=Invertebrate Zoology | chapter=Introduction to Invertebrates | publisher=Brooks / Cole | edition=7 | isbn=978-0-03-025982-1 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/2 2–9] | chapter-url=https://archive.org/details/isbn_9780030259821/page/2 }}</ref> living members of the [[phylum]] Bryozoa are divided into:<ref name="RuppertFoxBarnesBryozoa" /><ref name="Doherty2001EctoproctaInAnderson" />

{| class="wikitable"
! [[Class (biology)|Class]] !! [[Phylactolaemata]] !! [[Stenolaemata]] !! colspan="2" | [[Gymnolaemata]]
|- align="center"
! [[Order (biology)|Order]] !! [[Plumatellida]]<ref>{{cite web |url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156688 |title=ITIS Standard Report Page: Phylactolaemata |publisher=Integrated Taxonomic Information System |access-date=2009-08-12 |archive-date=18 January 2018 |archive-url=https://web.archive.org/web/20180118182014/https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156688 |url-status=live }}</ref>!! [[Cyclostomatida]] !! [[Ctenostomatida]] !! [[Cheilostomata]]
|- align="center"
! Environments
| [[Freshwater]] || Marine || colspan="2" | Mostly marine
|- align="center"
! Lip-like epistome overhanging mouth
| Yes || colspan="3" | none
|- align="center"
! Colony shapes
| Gelatinous masses or tubular branching structures<ref name="MassardGeimer2008FreshwaterBryoDiversity">{{cite journal |last1=Massard |first1=J.A. |year=2008 |title=Global diversity of bryozoans (Bryozoa or Ectoprocta) in freshwater |journal=[[Hydrobiologia]] |volume=595 |pages=93–99 |doi=10.1007/s10750-007-9007-3 |last2=Geimer |first2=Gaby |issue=1 |bibcode=2008HyBio.595...93M |s2cid=13057599}}</ref> || colspan="2" | Erect or encrusting<ref name="FishFish1996StudentsGuide" /> || Erect, encrusting or free-living
|- align="center"
! Exoskeleton material
| Gelatinous or membranous; unmineralized || Mineralized || [[Chitin]], gelatinous or membranous; unmineralized || Mineralized
|- align="center"
! Operculum ("lid")
| none || none<ref name="FishFish1996StudentsGuide">{{cite book |last=Fish |first=J.D. |author2=Fish, S. |title=A student's guide to the seashore |year=1996 |edition=2 |pages=[https://archive.org/details/studentsguideto00fish/page/418 418–419] |chapter=Bryozoa |isbn=978-0-521-46819-0 |publisher=Cambridge University Press |location=Cambridge |chapter-url=https://archive.org/details/studentsguideto00fish/page/418}}</ref> (except in family [[Eleidae]])<ref>{{cite journal |last1=Jablonski |first1=D. |last2=Lidgard |first2=S. |last3=Taylor |first3=P.D. |year=1997 |title=Comparative Ecology of Bryozoan Radiations: Origin of novelties in cyclostomes and Cheilostomes |journal=[[PALAIOS]] |volume=12 |pages=505–523 |doi=10.2307/3515408 |jstor=3515408 |issue=6 |bibcode=1997Palai..12..505J}}</ref> || None in most species || Yes (except in genus ''[[Bugula]]'')
|- align="center"
! Shape of lophophore
| U-shaped appearance{{pb}}(except in [[genus]] ''[[Fredericella]]'', whose lophophore is circular) || colspan="3" | Circular
|- align="center"
! How lophophore extended
| Compressing the whole body wall || Compressing the membranous sac{{pb}}(separate inner layer of [[epithelium]] that lines the coelom) || Compressing the whole body wall || Pulling inwards of a flexible section of body wall, or making an internal sac expand.
|- align="center"
! Types of zooid
| Autozooids only || Limited heterozooids, mainly gonozooids<ref name="HaywardRyland1985Cyclostome">{{cite book |last=Hayward |first=P.J. |author2=Ryland, J.S. |title=Cyclostome bryozoans |publisher=Linnean Society of London |year=1985 |page=7 |chapter=Key to the higher taxa of marine Bryozoa |isbn=978-90-04-07697-6 |chapter-url=https://books.google.com/books?id=cAsVAAAAIAAJ&q=Stenolaemata+Cyclostomata+heterozooid&pg=PA7 |access-date=2009-08-09 |archive-date=8 March 2023 |archive-url=https://web.archive.org/web/20230308183237/https://books.google.com/books?id=cAsVAAAAIAAJ&q=Stenolaemata+Cyclostomata+heterozooid&pg=PA7 |url-status=live }}</ref> || [[Stolon]]s and spines as well as autozooids<ref name="HaywardRyland1985Cyclostome" /> || Full range of types
|}

=== Fossil record ===
[[File:OilShaleFossilsEstonia.jpg |thumb |Bryozoan fossils in an Upper [[Ordovician]] oil shale ([[kukersite]]), northern [[Estonia]].]]
{{stereo image
 |image = Arhimedes3d.jpg
 |caption = Fossilized skeleton of [[Archimedes (bryozoan)|Archimedes Bryozoan]]
 |width = 450
 |height = 200
}}
Fossils of about 15,000 bryozoan species have been found. Bryozoans are among the three dominant groups of Paleozoic fossils.<ref name="Bryozoan Evolution">{{cite news |last1=McKinney |last2=Frank K |last3=Jeremy |title=Bryozoan Evolution |publisher=Boston: Unwin & Hyman, 1989}}</ref> Bryozoans with calcitic skeletons were a major source of the carbonate minerals that make up limestones, and their fossils are incredibly common in marine sediments worldwide from the Ordovician onward. However, unlike corals and other colonial animals found in the fossil record, Bryozoan colonies did not reach large sizes.<ref name="Phylum Bryozoa">{{cite book |last1=Ernst |first1=Andrej |title=Phylum Bryozoa |date=2020 |pages=11–56 |chapter=2- Fossil record and evolution of Bryozoa}}</ref> Fossil bryozoan colonies are typically found highly fragmented and scattered; the preservation of complete zoaria is uncommon in the fossil record, and relatively little study has been devoted to reassembling fragmented zoaria.<ref>{{cite journal |last1=Jackson |first1=Patrick N. Wyse |last2=Key |first2=Marcus M. Key Jr. |title=Epizoan and endoskeletozoan distribution across reassembled ramose stenolaemate bryozoan zoaria from the Upper Ordovician (Katian) of the Cincinnati Arch region, USA |journal=Australasian Palaeontological Memoirs |date=2019 |volume=52 |pages=169–178}}</ref> The largest known fossil colonies are branching trepostome bryozoans from Ordovician rocks in the United States, reaching 66 centimeters in height.<ref name="Phylum Bryozoa"/>

The oldest species with a [[biomineralization|mineralized]] skeleton occurs in the Lower [[Ordovician]].<ref name="Taylor2013" /> It is likely that the first bryozoans appeared much earlier and were entirely soft-bodied, and the Ordovician fossils record the appearance of mineralized skeletons in this phylum.<ref name="FuchsObstSundberg2009ComprMolPhyloOfBryozoa" /> By the [[Arenigian]] stage of the Early Ordovician [[Period (geology)|period]],<ref name="RichFenton1997Bryozoans" /><ref>{{cite journal |last1=Torsvik |first1=T.H. |date=January 1991 |journal=Geology |volume=19 |issue=1 |pages=7–10 |doi=10.1130/0091-7613(1991)019<0007:COPOB>2.3.CO;2 |title=Cambrian-Ordovician paleogeography of Baltica |last2=Ryan |first2=Paul D. |last3=Trench |first3=Allan |last4=Harper |first4=David A.T. |author-link4 = David Harper (palaeontologist) |bibcode = 1991Geo....19....7T }}</ref> about {{ma|480}}, all the modern [[Order (biology)|orders]] of [[Stenolaemata|stenolaemates]] were present,<ref name="DewelWinstonMcKinney2001Deconstructing" /> and the [[Ctenostomatida|ctenostome]] order of [[Gymnolaemata|gymnolaemates]] had appeared by the Middle Ordovician, about {{ma|465}}. The Early Ordovician fossils may also represent forms that had already become significantly different from the original members of the phylum.<ref name="DewelWinstonMcKinney2001Deconstructing" /> Ctenostomes with phosphatized soft tissue are known from the Devonian.<ref name="Olempska2012">{{cite journal | last1 = Olempska | first1 = E. | doi = 10.4202/app.2011.0200 | title = Exceptional soft-tissue preservation in boring ctenostome bryozoans and associated "fungal" borings from the Early Devonian of Podolia, Ukraine | journal = Acta Palaeontologica Polonica | year = 2012 | volume=57 | issue = 4 | pages=925–940 | doi-access = free }}</ref> Other types of [[filter feeder]]s appeared around the same time, which suggests that some change made the environment more favorable for this lifestyle.<ref name="RichFenton1997Bryozoans" /> Fossils of [[Cheilostomata|cheilostomates]], an order of gymnolaemates with mineralized skeletons, first appear in the Mid [[Jurassic]], about {{ma|172}}, and these have been the most abundant and diverse bryozoans from the [[Cretaceous]] to the present.<ref name="RichFenton1997Bryozoans" /> Evidence compiled from the last 100&nbsp;million years show that cheilostomatids consistently grew over cyclostomatids in territorial struggles, which may help to explain how cheilostomatids replaced cyclostomatids as the dominant marine bryozoans.<ref>{{cite journal |last=McKinney |first=F.K. |year=1994 |title=One hundred million years of competitive interactions between bryozoan clades: asymmetrical but not escalating |journal=Biological Journal of the Linnean Society |volume=56 |issue=3 |pages=465–481 |doi=10.1111/j.1095-8312.1995.tb01105.x}}</ref> Marine fossils from the [[Paleozoic]] era, which ended {{ma |251}}, are mainly of erect forms, those from the [[Mesozoic]] are fairly equally divided by erect and encrusting forms, and more recent ones are predominantly encrusting.<ref>{{cite book |last=Wood |first=R. |title=Reef evolution |publisher=Oxford University Press |year=1999 |pages=235–237 |isbn=978-0-19-857784-3 |url=https://books.google.com/books?id=H_ah6Hzib4AC&q=bryozoa+distribution+range&pg=PA235 |access-date=2009-08-11 |archive-date=8 March 2023 |archive-url=https://web.archive.org/web/20230308183234/https://books.google.com/books?id=H_ah6Hzib4AC&q=bryozoa+distribution+range&pg=PA235 |url-status=live }}</ref> Fossils of the soft, freshwater [[Phylactolaemata|phylactolaemates]] are very rare,<ref name="RichFenton1997Bryozoans" /> appear in and after the Late Permian (which began about {{ma |260}}) and consist entirely of their durable statoblasts.<ref name="MassardGeimer2008FreshwaterBryoDiversity" /> There are no known fossils of freshwater members of other classes.<ref name="MassardGeimer2008FreshwaterBryoDiversity" />

=== 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>

== Physiology ==

=== Feeding and excretion ===
Most species are [[filter feeder]]s that sieve small particles, mainly [[phytoplankton]] (microscopic floating plants), out of the water.<ref name="RuppertFoxBarnesBryozoa" /> The freshwater species ''[[Plumatella emarginata]]'' feeds on [[diatom]]s, [[green algae]], [[cyanobacteria]], non-[[photosynthetic]] bacteria, [[dinoflagellate]]s, [[rotifer]]s, [[protozoa]], small [[nematode]]s, and microscopic [[crustacean]]s.<ref name="CallaghanKarlson2002SummerDormancy" /> While the currents that bryozoans generate to draw food towards the mouth are well understood, the exact method of capture is still debated. All species also flick larger particles towards the mouth with a tentacle, and a few capture [[zooplankton]] (planktonic animals) by using their tentacles as cages. In addition the tentacles, whose surface area is increased by [[microvilli]] (small hairs and pleats), absorb [[organic compound]]s dissolved in the water.<ref name="RuppertFoxBarnesBryozoa" /> Unwanted particles may be flicked away by tentacles or shut out by closing the mouth.<ref name="RuppertFoxBarnesBryozoa" /> A study in 2008 showed that both encrusting and erect colonies fed more quickly and grew faster in gentle than in strong currents.<ref name="Pratt2008WhereFlowRight">{{cite journal|last=Pratt|first=M.C.|year=2008|title=Living where the flow is right: How flow affects feeding in bryozoans|journal= Integrative and Comparative Biology|volume=48|issue=6|pages=808–822|doi=10.1093/icb/icn052|pmid=21669834  |doi-access=free|url=https://scholarworks.smith.edu/context/bio_facpubs/article/1297/viewcontent/Living_where_the_flow_is_right.pdf}}</ref>

In some species the first part of the stomach forms a muscular [[gizzard]] lined with [[chitin]]ous teeth that crush armored prey such as [[diatom]]s. Wave-like [[peristalsis|peristaltic]] contractions move the food through the stomach for digestion. The final section of the stomach is lined with [[cilia]] (minute hairs) that compress undigested solids, which then pass through the [[intestine]] and out through the [[anus]].<ref name="RuppertFoxBarnesBryozoa" />

There are no [[nephridia]] ("little kidneys") or other [[excretory system|excretory]] organs in bryozoa,<ref name="Doherty2001EctoproctaInAnderson" /> and it is thought that [[ammonia]] [[molecular diffusion|diffuses]] out through the body wall and lophophore.<ref name="RuppertFoxBarnesBryozoa" /> More complex waste products are not excreted but accumulate in the [[polypide]], which degenerates after a few weeks. Some of the old polypide is recycled, but much of it remains as a large mass of dying cells containing accumulated wastes, and this is compressed into a "brown body". When the degeneration is complete, the cystid (outer part of the animal) produces a new polypide, and the brown body remains in the [[coelom]], or in the stomach of the new polypide and is expelled next time the animal [[defecate]]s.<ref name="RuppertFoxBarnesBryozoa" />

=== Respiration and circulation ===
There are no respiratory organs, [[heart]] or [[blood vessel]]s. Instead, zooids absorb oxygen and eliminate carbon dioxide through diffusion. Bryozoa accomplish diffusion through the use of either a thin membrane (in the case of [[anasca]]ns and some polyzoa) or through pseudopores located on the outer dermis of the zooid.<ref>{{Cite journal|last1=Ryland|first1=J.S.|title=Respiration in polyzoa (ectoprocta)|journal=Nature|volume=216|issue=5119|pages=1040–1041|doi=10.1038/2161040b0|year=1967|bibcode=1967Natur.216.1040R|s2cid=4207120}}</ref> The different bryozoan groups use various methods to share nutrients and oxygen between zooids: some have quite large gaps in the body walls, allowing the [[Coelom#Coelomic fluid|coelomic fluid]] to circulate freely; in others, the funiculi (internal "little ropes")<ref name="RanHouDictFuniculus" /> of adjacent zooids connect via small pores in the body wall.<ref name="RuppertFoxBarnesBryozoa" /><ref name="Nielsen2001InEncOfLifeSci" />

=== Reproduction and life cycles ===
[[File:ThecideanZalas.jpg|thumb|Encrusting cyclostome bryozoans (B), the one on the right showing swollen gonozooids; T = [[Thecideida|thecideide]] brachiopod and S = [[sabellida|sabellid]] worm tube; [[Jurassic]] of [[Poland]].]]

Zooids of all phylactolaemate species are simultaneous [[hermaphrodite]]s. Although those of many marine species are protandric, in other words function first as males and then as females, their colonies contain a combination of zooids that are in their male and female stages. In all species the [[ovary|ovaries]] develop on the inside of the body wall, and the [[testes]] on the funiculus connecting the stomach to the body wall.<ref name="Doherty2001EctoproctaInAnderson" /> Eggs and sperm are released into the coelom, and sperm exit into the water through pores in the tips of some of the tentacles, and then are captured by the feeding currents of zooids that are producing eggs.<ref name="RuppertFoxBarnesBryozoa" /> Some species' eggs are fertilized externally after being released through a pore between two tentacles, which in some cases is at the tip of a small projection called the "intertentacular organ" in the base of a pair of tentacles. Others' are fertilized internally, in the intertentacular organ or in the coelom.<ref name="RuppertFoxBarnesBryozoa" />

All phylactolaemates and stenolaemates, and most gymnolaemates, exhibit placentation, and has therefore lecithotrophic (non-feeding) larvae. Except for Cyclostomata and the small gymnolaemate family Epistomiidae, which are viviparous, all are brooders. Phylactolaemata brood their embryos in an internal brood sac, but Gymnolaemata both external membranous sacs, skeletal chambers (ovicells) and internal brooding sacs exist.<ref>{{cite journal | pmc=8042935 | date=2021 | last1=Nekliudova | first1=U. A. | last2=Schwaha | first2=T. F. | last3=Kotenko | first3=O. N. | last4=Gruber | first4=D. | last5=Cyran | first5=N. | last6=Ostrovsky | first6=A. N. | title=Three in one: Evolution of viviparity, coenocytic placenta and polyembryony in cyclostome bryozoans | journal=BMC Ecology and Evolution | volume=21 | issue=1 | page=54 | doi=10.1186/s12862-021-01775-z | doi-access=free | pmid=33845757 }}</ref><ref>{{cite journal | pmc=3489856 | date=2012 | last1=Moosbrugger | first1=M. | last2=Schwaha | first2=T. | last3=Walzl | first3=M. G. | last4=Obst | first4=M. | last5=Ostrovsky | first5=A. N. | title=The placental analogue and the pattern of sexual reproduction in the cheilostome bryozoan Bicellariella ciliata (Gymnolaemata) | journal=Frontiers in Zoology | volume=9 | issue=1 | page=29 | doi=10.1186/1742-9994-9-29 | doi-access=free | pmid=23098166 }}</ref>  The developing embryo relies on egg's yolk, extraembryonic nutrition (matrotrophy) or both.<ref>{{cite journal | url=https://ui.adsabs.harvard.edu/abs/2024PalJ...57.1306K/abstract | bibcode=2024PalJ...57.1306K | title=Unravelling the Evolution of Bryozoan Larvae | last1=Kotenko | first1=O. N. | last2=Ostrovsky | first2=A. N. | journal=Paleontological Journal | date=2024 | volume=57 | issue=11 | page=1306 | doi=10.1134/S0031030123110072 }}</ref>

In ctenostomes the mother provides a brood chamber for the fertilized eggs, and her polypide disintegrates, providing nourishment to the [[embryo]]. Stenolaemates produce specialized zooids to serve as brood chambers, and their eggs divide within this to produce up to 100 identical embryos.<ref name="Doherty2001EctoproctaInAnderson" />

Planktotrophic (feeding) larvae are only found in class Gymnolaemata: In the cheilostomatan suborder Malacostegina they are found in the two families Membraniporidae and Electridae, and in the three ctenostome families Alcyonidiidae, Farrellidae, and Hislopiidae. In addition there are a few unconfirmed records, like the solitary form Aethozoid where larvae has never been observed, but which is assumed to have planktotrophic larvae.<ref>{{cite journal | doi=10.1007/s13127-020-00443-2 | title=Morphology and life cycle of an epiphytic pherusellid ctenostome bryozoan from the Mediterranean Sea | date=2020 | last1=Decker | first1=Sebastian | last2=Wanninger | first2=Andreas | last3=Schwaha | first3=Thomas | journal=Organisms Diversity & Evolution | volume=20 | issue=3 | pages=417–437 | doi-access=free | bibcode=2020ODivE..20..417D }}</ref><ref>{{cite book | url=https://books.google.com/books?id=SK4HEAAAQBAJ&dq=planktotrophic+ctenostome+larvae&pg=PA134 | title=Phylum Bryozoa | isbn=978-3-11-058631-2 | last1=Schwaha | first1=Thomas | date=23 November 2020 | publisher=Walter de Gruyter GmbH & Co KG }}</ref><ref>{{cite journal | doi=10.1007/s12526-024-01409-9 | title=The first deep-sea ctenostome bryozoan from the Indian Ocean: ''Aethozoon flavum'' sp. nov. | date=2024 | last1=Schwaha | first1=Thomas | last2=Zeppilli | first2=Daniela | last3=González-Casarrubios | first3=Alberto | last4=Cepeda | first4=Diego | journal=Marine Biodiversity | volume=54 | issue=2 | page=19 | bibcode=2024MarBd..54...19S | doi-access=free }}</ref>

The [[Cleavage (embryo)|cleavage]] of bryozoan eggs is biradial, in other words the early stages are bilaterally symmetrical. It is unknown how the coelom forms, since the [[metamorphosis]] from [[larva]] to adult destroys all of the larva's internal tissues. In many animals the [[blastopore]], an opening in the surface of the early embryo, tunnels through to form the gut. However, in bryozoans the blastopore closes, and a new opening develops to create the mouth.<ref name="RuppertFoxBarnesBryozoa" />

Bryozoan larvae vary in form, but all have a band of cilia round the body which enables them to swim, a tuft of cilia at the top, and an adhesive sac that everts and anchors them when they settle on a surface.<ref name="RuppertFoxBarnesBryozoa" /> Some gymnolaemate species produce cyphonautes larvae which have little yolk but a well-developed mouth and gut, and live as [[plankton]] for a considerable time before settling. These larvae have triangular shells of [[chitin]], with one corner at the top and the base open, forming a hood round the downward-facing mouth.<ref name="Doherty2001EctoproctaInAnderson" /> In 2006 it was reported that the cilia of cyphonautes larvae use the same range of techniques as those of adults to capture food.<ref>{{cite journal|last=Strathmann|first=R.R.|date=March 2006|title=Versatile ciliary behaviour in capture of particles by the bryozoan cyphonautes larva|journal=Acta Zoologica|volume=87|issue=1|pages=83–89|doi=10.1111/j.1463-6395.2006.00224.x}}</ref> Species that brood their embryos form larvae that are nourished by large [[yolk]]s, have no gut and do not feed, and such larvae quickly settle on a surface.<ref name="RuppertFoxBarnesBryozoa" /> In all marine species the larvae produce cocoons in which they [[metamorphosis|metamorphose]] completely after settling: the larva's [[Epidermis (skin)|epidermis]] becomes the lining of the [[coelom]], and the internal tissues are converted to a food reserve that nourishes the developing zooid until it is ready to feed.<ref name="RuppertFoxBarnesBryozoa" /> The larvae of phylactolaemates produce multiple polypides, so that each new colony starts with several zooids.<ref name="RuppertFoxBarnesBryozoa" /> In all species the founder zooids then grow the new colonies by [[budding]] clones of themselves. In phylactolaemates, zooids die after producing several [[Cloning|clones]], so that living zooids are found only round the edges of a colony.<ref name="RuppertFoxBarnesBryozoa" />

Phylactolaemates can also reproduce asexually by a method that enables a colony's lineage to survive the variable and uncertain conditions of freshwater environments.<ref name="Doherty2001EctoproctaInAnderson" /> Throughout summer and autumn they produce disc-shaped statoblasts, masses of cells that function as "survival pods" rather like the [[Sponge#Asexual|gemmules of sponges]].<ref name="RuppertFoxBarnesBryozoa" /> Statoblasts form on the funiculus connected to the parent's gut, which nourishes them.<ref name="Doherty2001EctoproctaInAnderson" /> As they grow, statoblasts develop protective [[Bivalve shell|bivalve-like]] shells made of [[chitin]]. When they mature, some statoblasts stick to the parent colony, some fall to the bottom ("sessoblasts"), some contain air spaces that enable them to float ("floatoblasts"),<ref name="RuppertFoxBarnesBryozoa" /> and some remain in the parent's cystid to re-build the colony if it dies.<ref name="Doherty2001EctoproctaInAnderson" /> Statoblasts can remain dormant for considerable periods, and while dormant can survive harsh conditions such as freezing and [[desiccation]]. They can be transported across long distances by animals, floating vegetation, currents<ref name="RuppertFoxBarnesBryozoa" /> and winds,<ref name="Doherty2001EctoproctaInAnderson" /> and even in the guts of larger animals.<ref name="WoodOkamura1999Asajirella">{{cite journal|last1=Wood|first1=T.S.|date=December 1998|title=''Asajirella gelatinosa'' in Panama: a bryozoan range extension in the Western Hemisphere|journal=[[Hydrobiologia]]|volume=390|issue=1–3|pages=19–23|doi=10.1023/A:1003502814572|last2=Okamura|first2=Beth|s2cid=1525771}}</ref> When conditions improve, the valves of the shell separate and the cells inside develop into a zooid that tries to form a new colony. ''[[Plumatella emarginata]]'' produces both "sessoblasts", which enable the lineage to control a good territory even if hard times decimate the parent colonies, and "floatoblasts", which spread to new sites. New colonies of ''[[Plumatella repens]]'' produce mainly "sessoblasts" while mature ones switch to "floatoblasts".<ref name="CallaghanKarlson2002SummerDormancy" /> A study estimated that one group of colonies in a patch measuring {{convert|1|m2|sqft|sp=us|0}} produced 800,000 statoblasts.<ref name="RuppertFoxBarnesBryozoa" />
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Some freshwater bryozoans also avoid difficult conditions by producing statoblasts that lie dormant until conditions improve. For example, although conditions are favorable throughout the summer, most ''[[Plumatella emarginata]]'' statoblasts germinate in spring, very few in summer, and a significant numbers in autumn. Colonies that germinate in summer die quickly if [[crayfish]] are present, but survive about as well as spring and autumn colonies if there are no crayfish.<ref name="CallaghanKarlson2002SummerDormancy" />
-->

Cupuladriid Bryozoa are capable of both sexual and asexual reproduction. The sexually reproducing colonies (aclonal) are the result of a larval cupuladriid growing into an adult stage whereas the asexual colonies(clonal) are a result of a fragment of a colony of cupuladriids growing into its own colony. The different forms of reproduction in cupuladriids are achieved through a variety of methods depending on the morphology and classification of the zooid.<ref>{{cite journal |last1=O'Dea |first1=Aaron |last2=Jackson |first2=Jeremy B. C. |last3=Taylor |first3=Paul D. |last4=Rodríguez |first4=Felix |title=Modes of reproduction in recent and fossil cupuladriid bryozoans |volume=51 |issue=4 |journal=Palaeontology |year=2008 |pages=847–864|doi=10.1111/j.1475-4983.2008.00790.x |bibcode=2008Palgy..51..847O |s2cid=41016220 |doi-access=free }}</ref>

== Ecology ==

=== Habitats and distribution ===
Most marine species live in tropical waters at depths less than {{convert|100|m|ft fathom|sp=us}}. However, a few have been found in deep-sea [[Oceanic trench|trenches]],<ref>{{cite book|last=Emiliani|first=C.|author-link=Cesare Emiliani|title=Planet Earth: Cosmology, Geology, & the Evolution of Life & the Environment|publisher=Cambridge University Press|year=1992|pages=[https://archive.org/details/dictionaryofphys00emil/page/488 488–490]|chapter=The Paleozoic|isbn=978-0-19-503652-7|chapter-url=https://books.google.com/books?id=MfAGpVq8gpQC&q=bryozoa%20marine%20tropical&pg=PA489|access-date=2009-08-11|url=https://archive.org/details/dictionaryofphys00emil/page/488}}</ref> especially around [[cold seep]]s, and others near the [[Geographical pole|poles]].<ref name="Jones2006AppliedPaleo">{{cite book|last=Jones|first=R.W.|title=Applied palaeontology|publisher=Cambridge University Press|year=2006|page=116|chapter=Principal fossil groups|isbn=978-0-521-84199-3|chapter-url=https://books.google.com/books?id=KJBKC4qvV8AC&q=bryozoa+marine+tropical&pg=RA5-PA116|access-date=2009-08-11|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183244/https://books.google.com/books?id=KJBKC4qvV8AC&q=bryozoa+marine+tropical&pg=RA5-PA116|url-status=live}}</ref><ref>{{cite journal|last1=Kuklinski|first1=P.|year=2007|title=Comparison of bryozoan assemblages from two contrasting Arctic shelf regions |journal=[[Estuarine, Coastal and Shelf Science]]|volume=73|issue=3–4|pages=835–843|doi=10.1016/j.ecss.2007.03.024|last2=Bader|first2=Beate |bibcode = 2007ECSS...73..835K }}</ref>

The great majority of bryozoans are [[Sessility (zoology)|sessile]]. Typically, sessile bryozoans live on hard substrates including rocks, sand or shells.<ref>{{cite news|last1=Brusca|first1=R|last2=Brusca|first2=G|title=Invertebrates (2nd Edition)|publisher=Sunderland, MA: Sinauer Associates}}</ref> Boring bryozoans leave unique borehole traces after dissolving [[calcium carbonate]] substrates.<ref>{{Cite journal |last1=Johnson |first1=Mildred J. |last2=Lemer |first2=Sarah |last3=Hirose |first3=Masato |last4=Decker |first4=Sebastian H. |last5=Schwaha |first5=Thomas |date=2024-12-31 |title=Ecology of endolithic bryozoans: colony development, growth rates and interactions of species in the genus Immergentia |journal=Zoological Letters |volume=10 |issue=1 |pages=23 |doi=10.1186/s40851-024-00246-9 |doi-access=free |issn=2056-306X |pmc=11686985 |pmid=39736804}}</ref> Encrusting forms are much the commonest of these in shallow seas, but erect forms become more common as the depth increases.<ref name="Jones2006AppliedPaleo" /> An example of incrustation on pebbles and cobbles is found in the diverse Pleistocene bryozoans found in northern Japan, where fossils have been found of single stones covered with more than 20 bryozoan species.{{Sfn|Taylor|2020|p=159}} Sediments with smaller particles, like sand or silt, are usually unsuitable habitat for bryozoans, but tiny colonies have been found encrusting grains of coarse sand.{{Sfn|Taylor|2020|p=164}} Some bryozoan species specialize in colonizing marine algae, seagrasses, and even mangrove roots; the genus ''Amphibiobeania'' lives on the leaves of mangrove trees and is called "amphibious" because it can survive regular exposure to air at low tide.{{Sfn|Taylor|2020|p=162–163}}

There are a variety of "free-living" bryozoans that live un-attached to a substrate. A few forms such as ''[[Cristatella]]'' can move. Lunulitiform cheilostomes are one group of free-living bryozoans with mobile colonies. They form small round colonies un-attached to any substrate; colonies of the genus Selenaria have been observed to "walk" around using setae.{{Sfn|Taylor|2020|p=112–113}} Another cheilostome family, the Cupuladriidae, convergently evolved similarly shaped colonies capable of movement. When observed in an aquarium, Selenaria maculata colonies were recorded to crawl at a speed of one meter per hour, climb over each other, move toward light, and right themselves when turned upside-down.{{Sfn|Taylor|2020|p=79}} Later study of this genus showed that neuroelectrical activity in the colonies increased in correlation with movement toward light sources. It is theorized that the capacity for movement arose as a side effect when colonies evolved longer setae for unburying themselves from sediment.{{Sfn|Taylor|2020|p=79}}
[[File:Alcyonidium (Charleston, South Carolina, 1851).jpg|alt=Watercolor of alcyonidium|thumb|1851 watercolor of ''Alcyonidium'' by Jacques Burkhardt.]]
Other free-living bryozoans are moved freely by waves, currents, or other phenomena. An [[Antarctic]] species, ''Alcyonidium pelagosphaera'', consists of floating colonies. The pelagic species is between {{cvt|5.0 and 23.0|mm}} in diameter, has the shape of a hollow sphere and consists of a single layer of autozooids. It is still not known if these colonies are pelagic their whole life or only represents a temporarily and previously undescribed juvenile stage.<ref name="Jones2006AppliedPaleo" /><ref>{{Cite journal |url=https://link.springer.com/article/10.1007/BF00349118 |title= A pelagic bryozoan from Antarctica|journal=Marine Biology |date=October 1995 |volume=123 |issue=4 |pages=757–762 |doi=10.1007/BF00349118 |access-date=28 August 2017 |archive-date=3 August 2017 |archive-url=https://web.archive.org/web/20170803131921/https://link.springer.com/article/10.1007/BF00349118 |url-status=live |last1=Peck |first1=L. S. |last2=Hayward |first2=P. J. |last3=Spencer-Jones |first3=M. E. |bibcode= 1995MarBi.123..757P|s2cid=83529565 }}</ref> Colonies of the species ''Alcyonidium disciforme'', which is disc-shaped and similarly free-living, inhabit muddy seabeds in the Arctic and can sequester sand grains they have engulfed, potentially using the sand as ballast to turn themselves right-side-up after they have been overturned. Some bryozoan species can form bryoliths, sphere-shaped free-living colonies that grow outward in all directions as they roll about on the seabed.{{Sfn|Taylor|2020|p=114}}

In 2014 it was reported that the bryozoan ''[[Fenestrulina rugula]]'' had become a dominant species in parts of Antarctica. [[Global warming]] has increased the rate of scouring by [[iceberg]]s, and this species is particularly adept at recolonizing scoured areas.<ref>{{Cite news|title='Weedy thing' thrives as Antarctic shores warm|author=Matt McGrath|newspaper=BBC News|url=https://www.bbc.co.uk/news/science-environment-27831958|date=16 June 2014|access-date=16 June 2014|archive-date=17 June 2014|archive-url=https://web.archive.org/web/20140617181747/http://www.bbc.co.uk/news/science-environment-27831958|url-status=live}}</ref>

The phylactolaemates live in all types of freshwater environment – lakes and ponds, rivers and streams, and estuaries<ref name="MassardGeimer2008FreshwaterBryoDiversity" /> – and are among the most abundant sessile freshwater animals.<ref name="WoodLore2005PhylactolaemateMolPhylo">{{cite book|last=Wood|first=T.S.|author2=Lore M.|title=Bryozoan Studies 2004: Proceedings of the 13th International Bryozoology Association|editor=Moyano, H. I. |editor2=Cancino, J.M. |editor3=Wyse-Jackson, P.N.|publisher=Taylor & Francis Group|location=London|year=2005|pages=361–367|chapter=The higher phylogeny of phylactolaemate bryozoans inferred from 18S ribosomal DNA sequences|chapter-url=http://bryotechnologies.com/pdf/18S_rDNA.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://bryotechnologies.com/pdf/18S_rDNA.pdf |archive-date=2022-10-09 |url-status=live|access-date=2009-08-24}}</ref> Some ctenostomes are exclusively freshwater while others prefer brackish water but can survive in freshwater.<ref name="MassardGeimer2008FreshwaterBryoDiversity" /> Scientists' knowledge of freshwater bryozoan populations in many parts of the world is incomplete, even in some parts of Europe. It was long thought that some freshwater species occurred worldwide, but since 2002 all of these have been split into more localized species.<ref name="MassardGeimer2008FreshwaterBryoDiversity" />

Bryozoans grow in [[cloning|clonal]] colonies. A larval Bryozoan settles on a hard substance and produces a colony asexually through budding. These colonies can grow thousands of individual zooids in a relatively short period of time. Even though colonies of zooids grow through asexual reproduction, Bryozoans are hermaphrodites and new colonies can be formed through sexual reproduction and the generation of free swimming larvae. When colonies grow too large, however, they can split in two. This is the only case where asexual reproduction results in a new colony separate from its predecessor. Most colonies are stationary. Indeed, these colonies tend to be settled on immobile substances such as sediment and coarse substances. There are some colonies of freshwater species such as ''[[Cristatella|Cristatella mucedo]]'' that are able to move slowly on a creeping foot.<ref>{{cite web |last1=Ramel |first1=Gordon |date=2020-03-05 |title=Bryozoans: The Fascinating Colonies Of Phylum Ectoprocta |url=https://www.earthlife.net/inverts/bryozoa.html |access-date=2022-05-19 |website=Earthlife |archive-date=27 March 2022 |archive-url=https://web.archive.org/web/20220327220537/https://www.earthlife.net/inverts/bryozoa.html |url-status=live }}</ref>

=== Interactions with non-human organisms ===
[[File:Membranipora membranacea.jpg|thumb|Lacelike ''[[Membranipora membranacea]]'']]
Marine species are common on [[coral reef]]s, but seldom a significant proportion of the total [[biomass]]. In temperate waters, the skeletons of dead colonies form a significant component of shell gravels, and live ones are abundant in these areas.<ref name="MargulisSchwartz1998FiveKingdomsBryozoa" /> The marine lace-like bryozoan ''[[Membranipora membranacea]]'' produces spines in response to predation by several species of [[nudibranch|sea slug]]s (nudibranchs).<ref>{{cite journal|last1=Iyengar|first1=E.V.|year=2002|title=Specificity of cues inducing defensive spines in the bryozoan Membranipora membranacea|journal=Marine Ecology Progress Series|volume=225|pages=205–218|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=13449426|access-date=2009-08-18|doi=10.3354/meps225205|last2=Harvell|first2=CD|bibcode=2002MEPS..225..205I|doi-access=free|archive-date=26 January 2012|archive-url=https://web.archive.org/web/20120126225336/http://cat.inist.fr/?aModele=afficheN&cpsidt=13449426|url-status=live}}</ref> Other predators on marine bryozoans include fish, [[sea urchin]]s, [[pycnogonid]]s, [[crustacean]]s, [[mite]]s<ref>{{cite book|last=Hayward|first=P. J.|author2=Ryland, J.S.|title=Cyclostome bryozoans: keys and notes for the identification of the species|page=27|chapter=Predators|chapter-url=https://books.google.com/books?id=cAsVAAAAIAAJ&q=Bryozoa%20predator%20prey&pg=PA27|access-date=2009-08-18|isbn=978-90-04-07697-6|year=1985|publisher=Brill Archive|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183245/https://books.google.com/books?id=cAsVAAAAIAAJ&q=Bryozoa%20predator%20prey&pg=PA27|url-status=live}}</ref> and [[starfish]].<ref>{{cite journal|last1=Day|first1=R.W.|date=January 1981|title=Predation by ''Patiria miniata'' (Asteroidea) on bryozoans|journal=Oecologia|volume=51|issue=3|pages=300–309|doi=10.1007/BF00540898|pmid=28310012|last2=Osman|first2=R.W.|s2cid=19976956|bibcode=1981Oecol..51..300D}}</ref> In general marine [[echinoderms]] and [[molluscs]] eat masses of zooids by gouging pieces of colonies, breaking their mineralized "houses", while most [[arthropod]] predators on bryozoans eat individual zooids.<ref>{{cite book|last=McKinney|first=F.K.|author2=Taylor, P.D.|author3=Lidgard, S.|title=Predator-prey interactions in the fossil record|editor=Kelley, P.H.|editor2=Kowalewski, M.|editor3=Hansen, T.A.|publisher=Springer|year=2003|pages=239–246|chapter=Predation on Bryozoans and its Reflection in the Fossil Record|isbn=978-0-306-47489-7|chapter-url=https://books.google.com/books?id=bVlYBhq5hNYC&q=%22Predation%20on%20Bryozoans%20and%20its%20Reflection%20in%20the%20Fossil%20Record%22&pg=PA239|access-date=2009-08-18|archive-date=8 March 2023|archive-url=https://web.archive.org/web/20230308183233/https://books.google.com/books?id=bVlYBhq5hNYC&q=%22Predation%20on%20Bryozoans%20and%20its%20Reflection%20in%20the%20Fossil%20Record%22&pg=PA239|url-status=live}}</ref>

In freshwater, bryozoans are among the most important [[filter feeder]]s, along with [[sponge]]s and [[mussel]]s.<ref>{{cite journal|last=Wood|first=T.S.|date=October 2006|title=Freshwater Bryozoans of Thailand (Ectoprocta and Entoprocta)|journal=The Natural History Journal of Chulalongkorn University|volume=6|issue=2|pages=83–119|url=http://www.wright.edu/~tim.wood/documents/2006_ThaiBryos_000.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.wright.edu/~tim.wood/documents/2006_ThaiBryos_000.pdf |archive-date=2022-10-09 |url-status=live|access-date=2009-08-24}}</ref> Freshwater bryozoans are attacked by many predators, including snails, insects, and fish.<ref name="CallaghanKarlson2002SummerDormancy">{{cite journal|last1=Callaghan|first1=T.P.|date=June 2002|title=Summer dormancy as a refuge from mortality in the freshwater bryozoan ''Plumatella emarginata''|journal=Oecologia|volume=132|issue=1|pages=51–59|doi=10.1007/s00442-002-0946-0|pmid=28547286|last2=R.|first2=Karlson|s2cid=19925846|bibcode=2002Oecol.132...51C}}</ref>

In [[Thailand]] the [[introduced species]] ''[[Pomacea canaliculata]]'' (golden apple snail), which is generally a destructive [[herbivore]], has wiped out phylactolaemate populations wherever it has appeared. ''P. canaliculata'' also preys on a common freshwater gymnolaemate, but with less devastating effect. Indigenous snails do not feed on bryozoans.<ref name="predation_golden">{{cite journal|last=Wood|first=T.S.|date=May 2006|title=Heavy Predation on Freshwater Bryozoans by the Golden Apple Snail, ''Pomacea canaliculata''|journal=Natural History Journal of Chulalongkorn University|volume=6|issue=1|pages=31–36|url=http://www2.biology.sc.chula.ac.th/web%20of%20NHJCU%20PDF/6-1,31-36.pdf|access-date=2009-08-18|archive-url=https://web.archive.org/web/20111006013213/http://www2.biology.sc.chula.ac.th/web%20of%20NHJCU%20PDF/6-1,31-36.pdf|archive-date=6 October 2011|url-status=dead}}</ref>

Several species of the [[hydroid (zoology)|hydroid]] family [[Zancleidae]] have symbiotic relationships with bryozoans, some of which are beneficial to the hydroids while others are [[parasite|parasitic]]. Modifications appear in the shapes of some these hydroids, for example smaller tentacles or encrustation of the roots by bryozoans.<ref>{{cite journal|last=Puce|first=S.|year=2007|title=Symbiotic relationships between hydroids and bryozoans|journal=International Symbiosis Society Congress Number 5|volume=44|issue=1–3|pages=137–143|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=18888422|access-date=2009-08-18|archive-date=26 January 2012|archive-url=https://web.archive.org/web/20120126215431/http://cat.inist.fr/?aModele=afficheN&cpsidt=18888422|url-status=live}}</ref> The bryozoan ''[[Alcyonidium nodosum]]'' protects the [[whelk]] ''[[Burnupena papyracea]]'' against predation by the powerful and voracious [[rock lobster]] ''[[Jasus lalandii]]''. While whelk shells encrusted by the bryozoans are stronger than those without this reinforcement, chemical defenses produced by the bryozoans are probably the more significant deterrent.<ref>{{cite journal|last1=Gray|first1=C.A.|date=December 2005 |title=A symbiotic shell-encrusting bryozoan provides subtidal whelks with chemical defence against rock lobsters|journal=African Journal of Marine Science|volume=27|issue=3|pages=549–556| doi = 10.2989/18142320509504115|last2=McQuaid|first2=CD|last3=Davies-Coleman|first3=MT |bibcode=2005AfJMS..27..549G |s2cid=84531235}}</ref>

[[File:Bryolith (Banc d'Arguin, Mauritania).jpg|thumb|Mauritanian bryolith formed by circumrotatory growth of the bryozoan species ''[[Acanthodesia commensale]]'']]
In the [[Banc d'Arguin]] offshore [[Mauritania]] the species ''[[Acanthodesia commensale]]'', which is generally growing attached to gravel and hard-substrate, has formed a [[symbiosis|facultative symbiotic relationship]] with [[hermit crabs]] of the species ''Pseudopagurus cf. granulimanus'' resulting in egg-size structures known as bryoliths.<ref>{{cite journal|last1=Klicpera|first1=André|last2=Taylor|first2=Paul D.|last3=Westphal|first3=Hildegard|s2cid=15841444|title=Bryoliths constructed by bryozoans in symbiotic associations with hermit crabs in a tropical heterozoan carbonate system, Golfe d'Arguin, Mauritania|journal=Marine Biodiversity|date=30 July 2013|volume=43|issue=4|pages=429–444|doi=10.1007/s12526-013-0173-4|bibcode=2013MarBd..43..429K |url=https://doi.pangaea.de/10.1594/PANGAEA.836168|access-date=19 August 2019|archive-date=11 January 2020|archive-url=https://web.archive.org/web/20200111231258/https://doi.pangaea.de/10.1594/PANGAEA.836168|url-status=live}}</ref> Nucleating on an empty gastropod shell, the bryozoan colonies form multilamellar skeletal crusts that produce spherical encrustations and extend the living chamber of the hermit crab through helicospiral tubular growth.

Some phylactolaemate species are intermediate hosts for a group of [[myxozoa]] that have also been found to cause [[proliferative kidney disease]], which is often fatal in [[salmonid]] fish,<ref name="AndersonCanningOkamura2004BryozoanHostsForPKX">{{cite journal|last1=Anderson|first1=C.|year=1999|title=Molecular data implicate bryozoans as hosts for PKX (Phylum Myxozoa) and identify a clade of bryozoan parasites within the Myxozoa|journal=Parasitology|volume=119|issue=6|pages=555–561|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=1203412|access-date=2009-08-18|doi=10.1017/S003118209900520X|pmid=10633916|last2=Canning|first2=E.U.|last3=Okamura|first3=B.|s2cid=2851575|archive-date=26 January 2012|archive-url=https://web.archive.org/web/20120126223846/http://cat.inist.fr/?aModele=afficheN&cpsidt=1203412|url-status=live}}</ref> and has severely reduced wild fish populations in Europe and North America.<ref name="MassardGeimer2008FreshwaterBryoDiversity" />

''[[Membranipora membranacea]]'', whose colonies feed and grow exceptionally fast in a wide range of current speeds, was first noticed in the [[Gulf of Maine]] in 1987 and quickly became the most abundant organism living on [[kelp]]s.<ref name="Pratt2008WhereFlowRight" /> This [[invasive species|invasion]] reduced the kelp population by breaking their fronds,<ref name="RuppertFoxBarnesBryozoa" /> so that its place as the dominant "vegetation" in some areas was taken by another invader, the large [[alga]] ''[[Codium fragile]] tomentosoides''.<ref name="Pratt2008WhereFlowRight" /> These changes reduced the area of habitat available for local fish and invertebrates. ''M. membranacea'' has also invaded the northwest coast of the US.<ref name="RuppertFoxBarnesBryozoa" /> A few freshwater species have been also found thousands of kilometers from their native ranges. Some may have been transported naturally as statoblasts. Others more probably were spread by humans, for example on imported water plants or as stowaways on ships.<ref name="WoodOkamura1999Asajirella" />

=== Interaction with humans ===
[[Fish farms]] and hatcheries have lost stock to [[proliferative kidney disease]], which is caused by one or more [[myxozoan]]s that use bryozoans as alternate hosts.<ref name="AndersonCanningOkamura2004BryozoanHostsForPKX" />

Some fishermen in the [[North Sea]] have had to find other work because of a form of [[eczema]] (a skin disease) known as "[[Dogger Bank itch]]",<ref name="Jones2006AppliedPaleo" /> caused by contact with bryozoans that have stuck to nets and lobster pots.<ref>{{cite journal|last=Clin|first=B.|title=Professional photosensitive eczema of fishermen by contact with bryozoans: disabling occupational dermatosis|journal=International Maritime Health|volume=59|issue=1–4|pages=1–4|url=http://www.imh.mug.edu.pl/attachment/attachment/4761/2008t4.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.imh.mug.edu.pl/attachment/attachment/4761/2008t4.pdf |archive-date=2022-10-09 |url-status=live|access-date=2009-08-18|pmid=19227737|year=2008}}</ref>

Marine bryozoans are often responsible for [[biofouling]] on ships' hulls, on docks and marinas, and on offshore structures. They are among the first colonizers of new or recently cleaned structures.<ref name="MargulisSchwartz1998FiveKingdomsBryozoa">{{cite book|last=Margulis|first=L.|author-link=Lynn Margulis|author2=Schwartz K.V.|title=Five kingdoms: an illustrated guide to the phyla of life on earth|publisher=Elsevier|year=1998|page=[https://archive.org/details/fivekingdomsillu00marg_0/page/335 335]|chapter=Bryozoa|isbn=978-0-7167-3027-9|chapter-url=https://books.google.com/books?id=9IWaqAOGyt4C&q=bryozoa+ectoprocta+fouling|access-date=2009-08-20|url=https://archive.org/details/fivekingdomsillu00marg_0/page/335}}</ref> Freshwater species are occasional nuisances in water pipes, drinking water purification equipment, sewage treatment facilities, and the cooling pipes of power stations.<ref name="MassardGeimer2008FreshwaterBryoDiversity" /><ref>{{cite journal|last1=Wood|first1=T.S.|date=February 1999|title=Biofouling of wastewater treatment plants by the freshwater bryozoan, ''Plumatella vaihiriae''|journal=Water Research|volume=33|issue=3|pages=609–614|doi=10.1016/S0043-1354(98)00274-7|last2=Marsh|first2=Terrence G}}</ref>

A group of chemicals called [[bryostatin]]s can be extracted from the marine bryozoan ''[[Bugula neritina]]''. In 2001 pharmaceutical company [[GPC Biotech]] licensed bryostatin 1 from [[Arizona State University]] for commercial development as a treatment for cancer. GPC Biotech canceled development in 2003, saying that bryostatin 1 showed little effectiveness and some toxic side effects.<ref>{{cite web|url=http://www.marinebiotech.org/bryostatin.html|archive-url=https://web.archive.org/web/20070509175548/http://www.marinebiotech.org/bryostatin.html|url-status=dead|archive-date=9 May 2007|title=Bryostatin 1|date=19 June 2006|access-date=2009-08-20}}</ref> In January 2008 a [[clinical trial]] was submitted to the United States [[National Institutes of Health]] to measure the safety and effectiveness of Bryostatin 1 in the treatment of [[Alzheimer's disease]]. However, no participants had been recruited by the end of December 2008, when the study was scheduled for completion.<ref>{{cite web|url=http://clinicaltrials.gov/ct2/show/results/NCT00606164|title=Safety, Efficacy, Pharmacokinetics, and Pharmacodynamics Study of bryostatin 1 in Patients With Alzheimer's Disease|date=19 August 2009|publisher=National Institutes of Health|access-date=2009-08-20|archive-date=13 June 2011|archive-url=https://web.archive.org/web/20110613200451/http://clinicaltrials.gov/ct2/show/results/NCT00606164|url-status=live}}</ref> More recent work shows it has positive effects on cognition in patients with Alzheimer's disease with few side effects.<ref>{{cite journal | pmc=5438479 | year=2017 | last1=Nelson | first1=T. J. | last2=Sun | first2=M. K. | last3=Lim | first3=C. | last4=Sen | first4=A. | last5=Khan | first5=T. | last6=Chirila | first6=F. V. | last7=Alkon | first7=D. L. | title=Bryostatin Effects on Cognitive Function and PKCɛ in Alzheimer's Disease Phase IIA and Expanded Access Trials | journal=Journal of Alzheimer's Disease | volume=58 | issue=2 | pages=521–535 | doi=10.3233/JAD-170161 |doi-access=free | pmid=28482641 }}</ref> About {{convert|1000|kg|lb}} of bryozoans must be processed to extract {{convert|1|g|oz|frac=32}} of bryostatin, As a result, synthetic equivalents have been developed that are simpler to produce and apparently at least as effective.<ref>{{cite journal|last1=Wender|first1=P.A.|date=20 November 2002|title=The Practical Synthesis of a Novel and Highly Potent Analogue of Bryostatin|journal=Journal of the American Chemical Society|volume=124|issue=46|pages=13648–13649|doi=10.1021/ja027509+|pmid=12431074|last2=Baryza|first2=JL|last3=Bennett|first3=CE|last4=Bi|first4=FC|last5=Brenner|first5=SE
|last6=Clarke|first6=MO|last7=Horan|first7=JC|last8=Kan|first8=C|last9=Lacôte|first9=E|bibcode=2002JAChS.12413648W | display-authors = 8}}</ref>
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== Anatomy ==
[[File:Costazia costazi.jpg|thumb|''[[Costazia costazi]]'', a [[coralline]] bryozoan]]
Bryozoan skeletons grow in a variety of shapes and patterns: mound-shaped, lacy fans, branching twigs, and even corkscrew-shaped. Their [[skeleton]]s have numerous tiny openings, each of which is the home of a minute animal called a '''zooid'''. They also have a [[body cavity|coelomate]] body with a looped alimentary canal or gut, opening at the mouth and terminating at the [[anus]]. They feed with a specialized, [[cilia]]ted structure called a [[lophophore]], which is a crown of [[tentacle]]s surrounding the mouth. Their diet consists of small microorganisms, including [[diatom]]s and other unicellular [[algae]]. In turn, bryozoans are preyed on by grazing organisms such as [[sea urchin]]s and fish. Bryozoans do not have any defined respiratory, or circulatory systems due to their small size. However, they do have a simple nervous system and a hydrostatic skeletal system. Several studies have been undertaken on the crystallography of bryozoan skeletons, revealing a complex fabric suite of oriented [[calcite]] or [[aragonite]] crystallites within an organic matrix – see for example Hall ''et al.'' (2002).

[[File:Lophophores bryozoan.jpg|thumb|right240px|bryozoan lophophores]]
The tentacles of the bryozoans are ciliated, and the beating of the [[cilia]] creates a powerful current of water which drives water together with entrained food particles (mainly phytoplankton) towards the mouth. The gut is U-shaped, and consists of a [[pharynx]] which passes into the [[esophagus]], followed by the [[stomach]], which has three parts: the [[cardia]], the [[caecum]], and the [[pylorus]]. The pylorus leads to an intestine and a short [[rectum]] terminating at the anus, which opens outside the [[lophophore]]. In some groups, notably some ctenostomes, a specialized [[gizzard]] may be formed from the proximal part of the cardia. Gut and lophophore are the principal components of the [[polypide]]. Cyclical degeneration and regeneration of the polypide is characteristic of marine bryozoans. After the final polypide degeneration, the skeletal aperture of the feeding zooid may become sealed by the secretion of a terminal [[Septum (marine biology)|diaphragm]]. In many bryozoans only the zooids within a few generations of the growing edge are in an actively feeding state; older, more proximal zooids (e.g. in the interiors of bushy colonies) are usually dormant.

[[File:Freshwater Bryozoan234.JPG|thumb|left|Freshwater bryozoan]]
Because of their small size, bryozoans have no need of a blood system. Gaseous exchange occurs across the entire surface of the body, but particularly through the tentacles of the lophophore.

Bryozoans can reproduce both sexually and asexually. All bryozoans, as far as is known, are [[hermaphroditic]] (meaning they are both male and female). [[Asexual reproduction]] occurs by budding off new zooids as the colony grows, and is the main way by which a colony expands in size. If a piece of a bryozoan colony breaks off, the piece can continue to grow and will form a new colony. A colony formed this way is composed entirely of [[Cloning|clones]] (genetically identical individuals) of the first animal, which is called the '''ancestrula'''.

One species of bryozoan, ''Bugula neritina'', is of current interest as a source of [[cytotoxicity|cytotoxic]] chemicals, [[bryostatin]]s, under clinical investigation as anti-cancer agents.

== Fossils ==
[[File:07PaleoFTb15.JPG|thumb|Twig-like bryozoan fossils, Upper [[Ordovician]], near Brookville, Indiana.]]
[[File:Prasopora.JPG|thumb|''Prasopora'', a trepostome bryozoan from the [[Ordovician]] of Iowa.]]
[[File:BrownBodies.jpg|thumb|A section through ''Prasopora'' showing "brown bodies" in many of the zooecia; [[Ordovician]] of Iowa.]]
[[File:OilShaleFossilsEstonia.jpg|thumb|Bryozoans in an Ordovician [[oil shale]], northern [[Estonia]].]]
[[File:Bryozoa Hallopora1.jpg|thumb|Detail of [[Hallopora]] fossil specimen on display at [[National Museum of Natural History|Smithsonian]], Washington, DC]]
[[Fossil]] bryozoans are found in rocks beginning in the [[Early Ordovician]] as part of the [[Ordovician radiation]]. They were often major components of Ordovician seabed communities and, like modern-day bryozoans, played an important role in [[sediment]] stabilization and binding, as well as providing sources of food for other [[benthic]] organisms. During the [[Mississippian]] (354 to 323 million years ago) bryozoans were so common that their broken skeletons form entire [[limestone]] beds. Bryozoan fossil record comprises more than 1,000 described species. It is plausible that the Bryozoa existed in the [[Cambrian]] but were soft-bodied or not preserved for some other reason; perhaps they evolved from a [[phoronid]]-like ancestor at about this time.

Bryozoans are important members of sclerobiont (organisms which dwell on hard substrates such as shells and rocks) communities in the fossil record and in the Recent. For a review of sclerobiont evolution, history and ecology, see Taylor & Wilson (2003).

Most fossil bryozoans have mineralized skeletons. The skeletons of individual zooids vary from tubular to box-shaped and contain a terminal aperture from which the [[lophophore]] is protruded to feed. No pores are present in the great majority of Ordovician bryozoans, but skeletal evidence shows that [[epithelia]] were continuous from one zooid to the next.

With regard to the bryozoan groups lacking mineralized skeletons, the [[statoblasts]] of freshwater [[phylactolaemates]] have been recorded as far back as the [[Permian]], and the [[ctenostome]] fossils date from the [[Triassic]].

One of the most important events during bryozoan evolution was the acquisition of a calcareous skeleton and the related change in the mechanism of tentacle protrusion. The rigidity of the outer body walls allowed a greater degree of zooid contiguity and the evolution of massive, multiserial colony forms.

== Classification ==
The bryozoans were formerly considered to contain two subgroups: the ''ectoprocta'' and the ''[[entoprocta]]'', based on the similar bodyplans and mode of life of these two groups. (Some researchers also included the [[Cycliophora]], which are thought to be closely related to the entoprocta.) However, the ectoprocta are ''coelomate'' (possessing a [[body cavity]]) and their embryos undergo [[radial cleavage]], while the entoprocta are ''acoelemate'' and undergo [[spiral cleavage]]. Molecular studies are ambiguous about the exact position of the entoprocta, but do not support a close relationship with the ectoprocta. For these reasons, the entoprocta are now considered a phylum of their own.<ref>{{cite book|author = James W. Valentine|title = On the origins of phyla |year = 2004|publisher = University of Chicago Press}}</ref> The removal of the 150 species of entoprocta leaves ''bryozoa'' synonymous with ''ectoprocta''; some authors have adopted the latter name for the group, but the majority continue to use the former.

The closest relations of the bryozoans appear to be the [[brachiopod]]s. The sister group to this clade is still unclear but this seems most likely to be the [[phoronid]]s.
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== See also ==

*[[International Bryozoology Association]]
*[[List of prehistoric bryozoan genera]]
*[[Colony (biology)]]

== References ==
{{Reflist}}

==Bibliography==
* {{cite book |last1=Taylor |first1=Paul D. |title=Bryozoan Paleobiology |date=2020 |publisher=Natural History Museum |location=London |isbn=9781118455005}}

===Further reading===
* {{cite journal|last1=Hall|first1=S.R.|year=2002|title=Electron diffraction studies of the calcareous skeletons of bryozoans|journal=Journal of Inorganic Biochemistry|volume=88|pages=410–419| doi=10.1016/S0162-0134(01)00359-2 |pmid=11897358|last2=Taylor|first2=P.D. |last3=Davis|first3=SA|last4=Mann|first4=S|issue=3–4 |ref=none}}
*Hayward, P.G., J.S. Ryland and P.D. Taylor (eds.), 1992. ''Biology and Palaeobiology of Bryozoans'', Olsen and Olsen, Fredensborg, Denmark. {{ISBN?}}
* {{cite journal| doi=10.1093/icb/icq146| title=Life in the Colonies: Learning the Alien Ways of Colonial Organisms| year=2010| last1=Winston| first1=J. E.| journal=Integrative and Comparative Biology| volume=50| issue=6| pages=919–933| pmid=21714171| doi-access=free|ref=none}}
*Robison, R.A. (ed.), 1983. ''[[Treatise on Invertebrate Paleontology]], Part G, Bryozoa'' (revised). Geological Society of America and University of Kansas Press. {{ISBN?}}
*{{cite journal | pmid=17653353 | year=2007 | last1=Sharp | first1=J. H. | last2=Winson | first2=M. K. | last3=Porter | first3=J. S. | title=Bryozoan metabolites: An ecological perspective | volume=24 | issue=4 | pages=659–673 | doi=10.1039/b617546e | journal=Natural Product Reports | hdl=2160/3792 | url=http://cadair.aber.ac.uk/dspace/bitstream/2160/3792/1/bryozoan.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://cadair.aber.ac.uk/dspace/bitstream/2160/3792/1/bryozoan.pdf |archive-date=2022-10-09 |url-status=live |ref=none}}
* {{cite journal | doi=10.1016/S0012-8252(02)00131-9 | title=Palaeoecology and evolution of marine hard substrate communities | year=2003 | last1=Taylor | first1=P | journal=Earth-Science Reviews | volume=62 | issue=1 | pages=1–103 | url=http://www3.wooster.edu/geology/taylor%26Wilson2003.pdf | last2=Wilson | first2=M. A. | bibcode=2003ESRv...62....1T | url-status=dead | archive-url=https://web.archive.org/web/20090325233234/http://www.wooster.edu/geology/Taylor%26Wilson2003.pdf | archive-date=25 March 2009 | df=dmy-all |ref=none}}
* {{cite journal |title=The earliest bryozoan parasite: Middle Ordovician (Darriwilian) of Osmussaar Island, Estonia
 |journal= Palaeogeography, Palaeoclimatology, Palaeoecology |year=2014 |volume=414
 |pages=129–132 |url=https://www.researchgate.net/publication/265853181 |doi=10.1016/j.palaeo.2014.08.021|bibcode=2014PPP...414..129V  |ref=none|last1=Vinn |first1=Olev |last2=Wilson |first2=Mark A. |last3=Mõtus |first3=Mari-Ann |last4=Toom |first4=Ursula }}
* Woollacott, R.M. and R.L. Zimmer (eds), 1977. ''The Biology of Bryozoans'', Academic Press, New York. {{ISBN?}}

== External links ==

{{Commons category}}
*[http://bryozoa.net/ Index to Bryozoa] Bryozoa Home Page, was at RMIT; now bryozoa.net
*[http://bryozoa.net/links.html Other Bryozoan WWW Resources]
*[http://bryozoa.net/iba/index.html International Bryozoology Association] official website
*[http://neogenebryozoans.myspecies.info/ Neogene Bryozoa of Britain]
*[http://www.sms.si.edu/irlspec/IntroBryozoa.htm Bryozoan Introduction]
*[http://www.earthlife.net/inverts/bryozoa.html The Phylum Ectoprocta (Bryozoa)]
*[[:wikispecies:Bryozoa|Phylum Bryozoa]] at Wikispecies
*[https://web.archive.org/web/20141015183508/http://www.bio.umass.edu/biology/conn.river/bryozoa.html Bryozoans] in the [[Connecticut River]]
* [https://web.archive.org/web/20080720172410/http://www.tafi.org.au/zooplankton/imagekey/bryozoa/index.html Bryozoa Fact Sheet]

{{Animalia}}
{{Life on Earth}}
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[[Category:Bryozoans| ]]
[[Category:Protostome phyla]]
[[Category:Early Ordovician first appearances]]
[[Category:Extant Ordovician first appearances]]
[[Category:Taxa named by Christian Gottfried Ehrenberg]]