Polychaeta is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes. 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.
Polychaete
Phyllodoce rosea
The Pompeii worm lives at great depths by hydrothermal vents at temperatures up to 80 °C
Hesiocaeca methanicola lives at great depths on methane ice
The annelids, also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.
Annelid
This sabellid tubeworm is budding
Burgessochaeta setigera
Phylogenetic tree of early lophophorates