Polychseta

Polychseta, the order of worms including those members of the class Chsetopoda or bristle-bearing worms which have numerous setse or bristles; these are united into bundles and placed on lateral processes of the body known as parapodia. In addition to these, there are other lateral appendages - the cirri and branchiae - which are mainly concerned in respiration. The Polyohseta are all marine. The order is subdivided into the Errantia, which are free and carnivorous; and the Tubicola, which live in tubes which are usually fixed; while the animals feed on vegetable matter. As examples of the former may be cited Aphrodite, or the Sea-hare, and the centipede-like worms, Nereis, Phyllodoce, etc.; of the latter there are the Lob-worms (Arenicola), which live in burrows in sand, and Serpula or Spirorbis, which form calcareous tubes.