What is Class Polychetae - Marine Worms?

The polychaetes differ from the oligochaetes in several ways. The name itself suggests one of the differences. The prefix "poly" means "many," as opposed to "oligo," meaning "few." Thus, the polychaetes have many hair-like bristles. They also have paired appendages called parapodia that bear the numerous setae. Parapodia have several functions, including helping the worms swim or crawl, as well as providing an anchoring mechanism. Parapodia, in addition, provide increased surface area for gas exchange. Most polychaetes live in marine habitats, and they can be found either living as plankton, crawling on the sea floor, or living in tubes, which the worms secrete around themselves.

Polychaetes also differ from the other two groups in that their anterior is better developed. They have a definite head region with sensory apparatus that include light-sensitive eyes.