polychaete n : chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles [syn: polychete, polychaete worm, polychete worm]
- alternative spelling of polychete
The Polychaeta or polychaetes are a 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. Indeed the polychaetes are sometimes referred to as bristle worms. More than 10,000 species are described in this class. Common representatives include the lugworm (Arenicola marina) and the sandworm or clam worm Nereis.
Anatomy and physiologyThe polychaetes' paddle-like and highly vascularized parapodia are used for movement and act as the annelid's primary respiratory surfaces (parapodia can be thought of as kinds of external gills that are also used for locomotion). Polychaeta also have well-developed heads compared to other annelids.
EcologyPolychaetes are extremely variable in both form and lifestyle and include a few taxa that swim among the plankton. Most burrow or build tubes on the bottom, and some live as commensals. A few are parasitic. The mobile forms or Errantia tend to have well-developed sense organs and jaws, while the Sedentaria (or stationary forms) lack them but may have specialized gills or tentacles used for respiration and deposit or filter feeding, e.g., fanworms.
A few groups have evolved to live in terrestrial environments, like Namanereidinae with many terrestrial species, but are restricted to humid areas. Some have even evolved cutaneous invaginations for aerial gas exchange.
One notable polychaete, the Pompeii worm (Alvinella pompejana) is endemic to the hydrothermal vents of the Pacific Ocean. Pompeii worms are thought to be the most heat-tolerant complex animals known.
Lamellibrachia luymesi is a cold seep tube worm that reaches lengths of over 3 meters and may be the most long lived animal at over 250 years old.
Evolutionary historyThe oldest crown group polychaetes fossils come from the Sirius Passet , which is tentatively dated to the lower-middle Atdabanian (early Cambrian). Many of the more famous Burgess Shale organisms, such as Canadia and Wiwaxia, may also have polychate affinites. An even older fossil, Cloudina, dates to the terminal Ediacaran period; this has been interpreted as an early polychaete, although consensus is absent.
Being soft bodied, the fossil record of polychaetes is dominated by their fossilized jaws, known as scolecodonts, and the mineralized tubes that some of them secrete.
Taxonomy and systematicsTaxonomically, the polychaetes are thought to be paraphyletic, meaning that as a group it contains its most recent common ancestor, but does not contain all the descendants of that ancestor. Groups that may be descended from the polychaetes include the earthworms, the 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.
- Subclass Palpata
- Order Aciculata
- Basal or incertae sedis
- Suborder Eunicida
- Suborder Phyllodocida
- Family Acoetidae
- Family Alciopidae
- Family Aphroditidae
- Family Chrysopetalidae
- Family Eulepethidae
- Family Glyceridae
- Family Goniadidae
- Family Hesionidae
- Family Ichthyotomidae
- Family Iospilidae
- Family Lacydoniidae
- Family Lopadorhynchidae
- Family Myzostomatidae
- Family Nautillienellidae
- Family Nephtyidae
- Family Nereididae
- Family Paralacydoniidae
- Family Pholoidae
- Family Phyllodocidae
- Family Pilargidae
- Family Pisionidae
- Family Polynoidae
- Family Pontodoridae
- Family Sigalionidae
- Family Sphaeodoridae
- Family Syllidae
- Family Typhloscolecidae
- Family Tomopteridae
- Order Canalipalpata
- Basal or incertae sedis
- Suborder Sabellida
- Suborder Spionida
- Suborder Terebellida
- Family Acrocirridae (sometimes placed in Spionida)
- Family Alvinellidae
- Family Ampharetidae
- 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 Pectinariidae
- Family Poeobiidae (sometimes own suborder Poeobiida or included in Flabelligerida)
- Family Sternaspidae (sometimes own suborder Sternaspida)
- Family Terebellidae
- Family Trichobranchidae
- Order Aciculata
- Subclass Scolecida
- Epitoky, a form of reproduction of Polychaetae.
- Campbell, Reece, and Mitchell. Biology. 1999.
- Special issue dedicated to polychaete published in Marine Ecology. Read the article abstracts online
polychaete in Catalan: Poliquet
polychaete in Czech: Mnohoštětinatci
polychaete in German: Vielborster
polychaete in Estonian: Hulkharjasussid
polychaete in Spanish: Polychaeta
polychaete in Esperanto: Poliĥetoj
polychaete in French: Polychaeta
polychaete in Indonesian: Polychaeta
polychaete in Italian: Polychaeta
polychaete in Hebrew: רב זיפיות
polychaete in Lithuanian: Daugiašerės žieduotosios kirmėlės
polychaete in Macedonian: Полихети
polychaete in Dutch: Borstelwormen
polychaete in Japanese: 多毛類
polychaete in Norwegian: Havbørsteormer
polychaete in Polish: Wieloszczety
polychaete in Portuguese: Polychaeta
polychaete in Russian: Многощетинковые черви
polychaete in Simple English: Polychaeta
polychaete in Slovak: Mnohoštetinavce
polychaete in Slovenian: Mnogoščetinci
polychaete in Serbian: Многочекињасти црви
polychaete in Finnish: Monisukasmadot
polychaete in Swedish: Havsborstmaskar
polychaete in Thai: โพลีคีทา
polychaete in Turkish: Deniz halkalı solucanları
polychaete in Ukrainian: Поліхети