What is Polychaete?
{{Taxobox | name = Polychaetes | image = Libr0409.jpg | image_width = 250px | image_caption = A variety of marine worms <br />from ''Das Meer'', M.J. Schleiden (1804–1881). | regnum = [[Animal]]ia | phylum = [[Annelida]] | classis = '''Polychaeta''' | classis_authority = Grube, 1850}} [[File:Spirobrancheus giganteus.jpg|right|230px|thumb|Christmas tree worms (''Spirobranchus giganteus'') from [[East Timor]].]] [[File:Featherduster 300.jpg|thumb|right|230px|''Sabellastarte indica'']] [[File:Tomopteriskils.jpg|thumb|right|230px|''Tomopteris'' from [[plankton]]]] '''Polychaetes''', or '''bristle worms''', are a [[class (biology)|class]] of [[annelid]] worms. They are generally found in a [[Ocean|marine]] [[environment]]. There are more than 10,000 known [[species]] in this class. They are ancient animals, dating back to 518 million years ago. They are first found in the early [[Cambrian]] fossil beds of [[Sirius Passet]] in [[Greenland]].<ref>Morris S.C. & Peel J. S. 2008. The earliest annelids: Lower Cambrian polychaetes from the Sirius Passet lagerstätte, Peary Land, North Greenland. ''Acta Palaeontologica Polonica'' '''53''': 137. [http://www.app.pan.pl/article/item/app53-137.html]</ref> Each of their body [[segment]]s has some fleshy protrusions that stand out. These 'parapodia' have many [[bristle]]s, which are made of [[chitin]]. This is different from the [[Oligochaeta]], which are similar in form, but only have a few bristles. Common species are the [[lugworm]], and the [[clam worm]] ''[[Nereis]]'' (which is sometimes also called a 'sandworm').<ref name=Barnes>Barnes, Robert D. 1982. ''Invertebrate zoology''. Philadelphia, PA: Holt-Saunders International. pp. 469–525. {{ISBN|0-03-056747-5}}.</ref> == Description == Polychaetes are segmented worms, generally less than {{convert|10|cm|in}} in length, although ranging at the extremes from {{convert|1|mm|in}} to {{convert|3|m|ft}}. They are often brightly coloured, and may be [[Iridescence|iridescent]] or even [[Bioluminescence|luminescent]]. Each segment