Editing Polychaete (section)

{{short description|Class of annelid worms}}
{{Redirect|Polychaeta|the genus of flies|Polychaeta (fly)}}
{{Paraphyletic group
| fossil_range = {{fossilrange|Cambrian Stage 3|0|[[Cambrian]] <small>(or earlier?)</small> – present}}
| name = Polychaetes
| image = Libr0409.jpg
| image_caption = "A variety of marine worms": plate from ''Das Meer'' by [[Matthias Jakob Schleiden|M. J. Schleiden]] (1804–1881)
| image_upright = 1.2
| auto = yes
| taxon = Polychaeta
| authority = Grube, 1850
| includes = *[[Oweniidae]]
*[[Magelonidae]]
*[[Chaetopteridae]]<ref name="Struck2011">{{Cite journal | last1 = Struck | first1 = T. H. | last2 = Paul | first2 = C. | last3 = Hill | first3 = N. | last4 = Hartmann | first4 = S. | last5 = Hösel | first5 = C. | last6 = Kube | first6 = M. | last7 = Lieb | first7 = B. | last8 = Meyer | first8 = A. | last9 = Tiedemann | first9 = R. | last10 = Purschke | doi = 10.1038/nature09864 | first10 = G. N. | last11 = Bleidorn | first11 = C. | title = Phylogenomic analyses unravel annelid evolution | journal = Nature | volume = 471 | issue = 7336 | pages = 95–98 | year = 2011 | pmid =  21368831| bibcode = 2011Natur.471...95S | s2cid = 4428998 }}</ref>
*[[Amphinomida]]
*[[Errantia]]
*[[Sedentaria]]
| excludes = *[[Sipuncula]]
*[[Myzostomida]]
*[[Clitellata]]
}}

'''Polychaeta''' ({{IPAc-en|ˌ|p|ɒ|l|ɪ|ˈ|k|iː|t|ə}}) is a [[paraphyletic]]<ref name="Struck2011" /> class of generally marine [[Annelid|annelid worms]], [[common name|commonly called]] '''bristle worms''' or '''polychaetes''' ({{IPAc-en|ˈ|p|ɒ|l|ɪ|ˌ|k|iː|t|s}}). Each body segment has a pair of fleshy protrusions called [[parapodia]] that bear many bristles, called [[chaeta]]e, which are made of [[chitin]]. More than 10,000 species are described in this class.  Common representatives include the [[lugworm]] (''Arenicola marina'') and the [[Alitta virens|sandworm]] or [[Alitta succinea|clam worm]] ''Alitta''.

Polychaetes as a class are robust and widespread, with species that live in the coldest ocean temperatures of the [[abyssal plain]], to forms which tolerate the extremely high temperatures near [[hydrothermal vent]]s. Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as [[plankton]] near the surface, to a 2- to 3-cm specimen (still unclassified) observed by the robot ocean probe [[Nereus (underwater vehicle)|''Nereus'']] at the bottom of the [[Challenger Deep]], the deepest known spot in the Earth's oceans.<ref>[http://ns.gov.gu/geography.html Geography of Guam ] {{Webarchive|url=https://web.archive.org/web/19961027163532/http://ns.gov.gu/geography.html |date=1996-10-27 }} ns.gov.gu Accessed Oct. 8, 2009</ref> Only 168 species (less than 2% of all polychaetes) are known from fresh waters.<ref>{{cite journal |first1=Cristopher |last1=Glasby |first2=Tarmo |last2=Timm |year=2008 |title=Global diversity of polychaetes (Polychaeta: Annelida) in freshwater |journal=[[Hydrobiologia]] |volume=595 |issue=1: Freshwater Animal Diversity Assessment |pages=107–115 |doi=10.1007/s10750-007-9008-2 |citeseerx=10.1.1.655.4467 |s2cid=13143924 |editor1=E. V. Balian |editor2=C. Lévêque |editor3=H. Segers |editor4=K. Martens }}</ref>