Editing Flagellum (section)

====Evolution and occurrence====
{{further|Evolution of flagella}}

Eukaryotic flagella or cilia, probably an ancestral characteristic,<ref>{{cite journal |last1=Yubuki |first1=Naoji |last2=Leander |first2=Brian S. |title=Evolution of microtubule organizing centers across the tree of eukaryotes |journal=The Plant Journal |date=July 2013 |volume=75 |issue=2 |pages=230–244 |doi=10.1111/tpj.12145 | pmid = 23398214 |doi-access=free}}</ref> are widespread in almost all groups of eukaryotes, as a relatively perennial condition, or as a flagellated life cycle stage (e.g., [[zoid]]s, [[gamete]]s, [[zoospore]]s, which may be produced continually or not).<ref>{{cite book |first=J.A. |last=Raven |chapter=The flagellate condition |chapter-url=https://books.google.com/books?id=GURZDwAAQBAJ&pg=PA27 |title={{harvnb|Leadbeater|Green|2000|pp=27–48}} |year=2000 |publisher=CRC Press |isbn=9781482268225 }}<!-- Pages from table of contents --></ref><ref name = "Webster_Weber_2007">{{cite book |last1=Webster |first1=John |last2=Weber |first2=Roland | title = 2007 | chapter = Spores of Fungi | date = 25 January 2007 | edition = 3rd | location = Cambridge | publisher = Cambridge University Press | pages = 23–24 | isbn = 9781139461504 | chapter-url = https://books.google.com/books?id=SApIn7IEnucC&pg=PT64 }}</ref><ref name = "Adl_2012" />

The first situation is found either in specialized cells of multicellular organisms (e.g., the [[choanocyte]]s of [[sponges]], or the ciliated [[epithelia]] of [[metazoan]]s), as in [[ciliate]]s and many eukaryotes with a "flagellate condition" (or "monadoid [[:de:Organisationsstufe|level of organization]]", see [[flagellate#Flagellates as organisms: the Flagellata|Flagellata]], an artificial group).

Flagellated lifecycle stages are found in many groups, e.g., many [[green algae]] (zoospores and male gametes), [[bryophyte]]s (male gametes), [[pteridophyte]]s (male gametes), some [[gymnosperm]]s ([[cycad]]s and ''[[Ginkgo]]'', as male gametes), centric [[diatom]]s (male gametes), [[brown algae]] (zoospores and gametes), [[oomycete]]s (assexual zoospores and gametes), [[hyphochytrid]]s (zoospores), [[labyrinthulomycetes]] (zoospores), some [[apicomplexan]]s (gametes), some [[radiolarian]]s (probably gametes),<ref>{{cite journal |last1=Lahr |first1=Daniel J. G. |last2=Parfrey |first2=Laura Wegener |last3=Mitchell |first3=Edward A. D. |last4=Katz |first4=Laura A. |last5=Lara |first5=Enrique |title=The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms |journal=Proceedings of the Royal Society B: Biological Sciences |date=22 July 2011 |volume=278 |issue=1715 |pages=2081–2090 |doi=10.1098/rspb.2011.0289 |pmid = 21429931 | pmc = 3107637}}</ref> [[foraminiferan]]s (gametes), [[Phytomyxea|plasmodiophoromycete]]s (zoospores and gametes), [[myxogastrid]]s (zoospores), [[metazoan]]s (male gametes), and [[chytrid]] fungi (zoospores and gametes).

Flagella or cilia are completely absent in some groups, probably due to a loss rather than being a primitive condition. The loss of cilia occurred in [[red algae]], some green algae ([[Zygnematophyceae]]), the [[gymnosperm]]s except cycads and ''Ginkgo'', [[angiosperm]]s, pennate [[diatom]]s, some [[apicomplexan]]s, some [[amoebozoan]]s, in the sperm of some [[metazoan]]s,<ref name = "Austin_1995">{{cite book |last1=Austin |first1=CR |editor1-last=Grudzinskas |editor1-first=Jurgis Gediminas |editor2-last=Yovich |editor2-first=J L |title=Gametes - the spermatozoon |date=1995 |publisher=Cambridge University Press |location=Cambridge |isbn=9780521479967 |url = https://books.google.com/books?id=UEvbQcZ7e1oC}}</ref> and in [[fungi]] (except [[chytrid]]s).