Polychaetes, or bristle worms, are a very common and diverse class of worms with over 10,000 species described so far. Commonly overlooked, these mostly marine worms can be brightly coloured and are to be found in tubes and burrows in the sand and mud of the beach to the depths of the ocean or even just free-living in the water. They all have bristles on their segmented bodies - in fact 'polychaeta' means 'many bristles'. They come in an impressive range of sizes from just 1mm to 3m long.
Scientific name: Polychaeta
The Polychaeta or polychaetes are a polyphyletic 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, 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.
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 extreme 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 2–3 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 freshwaters.