Editing Bryozoa (section)

=== 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>