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Polychaeta

Polychaetes
Fossil range: 530–0 Ma
Cambrian (or earlier?) - present
"A variety of marine worms": plate from Das Meer by M.J. Schleiden (1804–1881).
"A variety of marine worms": plate from Das Meer by M.J. Schleiden (1804–1881).
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Polychaeta
Grube, 1850
Included groups

Palpata
Scolecida

Excluded groups

Echiura
Chaetopteridae


Palpata
Scolecida

Echiura
Chaetopteridae

The Polychaeta /ˌpɒlɪˈktə/ 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. As such, 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 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 (still unclassified) 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 (less than 2% of all polychaetes) are known from fresh waters.


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