Editing Bryozoa (section)

== 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>