page_title: Polychaete
section_title: Taxonomy and systematics
hierarchical_section_title: Polychaete / Taxonomy and systematics
caption_attribution_description: English: Polychaete worm Nereis pelagica Русский: Многощетинковый кольчатый червь Nereis pelagica
context_page_description: The Polychaeta, also known as the bristle worms or polychaetes, are a paraphyletic class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. More than 10,000 species are described in this class. Common representatives include the lugworm and the sandworm or 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 vents. 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 observed by the robot ocean probe Nereus at the bottom of the Challenger Deep, the deepest known spot in the Earth's oceans. Only 168 species are known from fresh waters.
context_section_description: Taxonomically, polychaetes are thought to be paraphyletic, meaning the group excludes some descendants of its most recent common ancestor.  Groups that may be descended from the polychaetes include the oligochaetes (earthworms and leeches), sipunculans, and echiurans.  The Pogonophora and Vestimentifera were once considered separate phyla, but are now classified in the polychaete family Siboglinidae.
  Much of the classification below matches Rouse & Fauchald, 1998, although that paper does not apply ranks above family.
  Older classifications recognize many more (sub)orders than the layout presented here. As comparatively few polychaete taxa have been subject to cladistic analysis, some groups which are usually considered invalid today may eventually be reinstated.
  These divisions were shown to be mostly paraphyletic in recent years.
  Basal or incertae sedis
  Family Diurodrilidae
  Family Histriobdellidae
  Family Nerillidae
  Family Parergodrilidae
  Family Potamodrilidae
  Family Psammodrilidae
  Family Spintheridae
  Family Protodriloididae
  Family Saccocirridae
  Order Haplodrili
  Order Myzostomida
  Family Endomyzostomatidae
  Family Asteromyzostomatidae
  Family Myzostomidae
  Subclass Palpata
  Family Protodrilidae
  Family Polygordiidae
  Subclass Aciculata
  Family Levidoridae
  Order Amphinomida
  Family Amphinomidae
  Family Euphrosinidae
  Order Eunicida
  Family Dorvilleidae
  Family Eunicidae
  Family Hartmaniellidae
  Family Ichthyotomidae
  Family Lumbrineridae
  Family Oenonidae
  Family Onuphidae
  Order Phyllodocida
  Suborder Aphroditiformia
  Family Acoetidae
  Family Aphroditidae
  Family Eulepethidae
  Family Iphionidae
  Family Pholoidae
  Family Polynoidae
  Family Sigalionidae
  Suborder Glyceriformia
  Family Glyceridae
  Family Goniadidae
  Family Lacydoniidae
  Family Paralacydoniidae
  Suborder Nereidiformia
  Family Antonbruunidae
  Family Chrysopetalidae
  Family Hesionidae
  Family Nereididae
  Family Pilargidae
  Family Syllidae
  Suborder Phyllodocida incertae sedis
  Family Iospilidae
  Family Nautiliniellidae
  Family Nephtyidae
  Family Typhloscolecidae
  Family Tomopteridae
  Suborder Phyllodociformia
  Family Alciopidae
  Family Lopadorhynchidae
  Family Phyllodocidae
  Family Pontodoridae
  Subclass Sedentaria
  Family Chaetopteridae
  Infraclass Canalipalpata
  Order Sabellida
  Family Caobangidae
  Family Fabriciidae
  Family Oweniidae
  Family Sabellariidae
  Family Sabellidae
  Family Serpulidae
  Family Siboglinidae (formerly the phyla Pogonophora & Vestimentifera)
  Order Spionida
  Suborder Spioniformia
  Family Apistobranchidae
  Family Longosomatidae
  Family Magelonidae
  Family Poecilochaetidae
  Family Spionidae
  Family Trochochaetidae
  Family Uncispionidae
  Order Terebellida
  Suborder Cirratuliformia
  Family Acrocirridae (sometimes placed in Spionida)
  Family Cirratulidae (sometimes placed in Spionida)
  Family Ctenodrilidae (sometimes own suborder Ctenodrilida)
  Family Fauveliopsidae (sometimes own suborder Fauveliopsida)
  Family Flabelligeridae (sometimes suborder Flabelligerida)
  Family Flotidae (sometimes included in Flabelligeridae)
  Family Poeobiidae (sometimes own suborder Poeobiida or included in Flabelligerida)
  Family Sternaspidae (sometimes own suborder Sternaspida)
  Suborder Terebellomorpha
  Family Alvinellidae
  Family Ampharetidae
  Family Pectinariidae
  Family Terebellidae
  Family Trichobranchidae
  Infraclass Scolecida
  Family Arenicolidae
  Family Capitellidae
  Family Cossunidae
  Family Maldanidae
  Family Opheliidae
  Family Orbiniidae
  Family Paraonidae
  Family Scalibregmatidae
  Order Capitellida (nomen dubium)
  Order Cossurida (nomen dubium)
  Order Opheliida (nomen dubium)
  Order Orbiniida (nomen dubium)
  Order Questida (nomen dubium)
  Order Scolecidaformia (nomen dubium)
  Subclass Echiura
  Order Bonelliida
  Family Bonelliidae
  Family Ikedidae
  Order Echiurida
  Family Echiuridae
  Family Thalassematidae
  Family Urechidae
caption: Rag worms can be dangerous to touch, giving painful burns
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