Polychaetes are chiefly aquatic and most species are marine. They are easily recognized by the paddle-like "legs" that protrude from the sides of each body segment. These appendages, which impart a centipede-like appearance, bear numerous tiny hairs that aid in locomotion and, in some groups, create water currents for feeding. The abundance of these hairs is the basis for the name of these worms (poly=many; chaeta=hairs).
Polychaetes have diverse eating habits, depending on their lifestyle. Many
polychaetes live in tubes, and are filter feeders. By moving their appendages
within these tubes, they create a water current that draws smaller particles
to their mouths. Others are active hunters, swimming through the water and grasping
prey, such as small worms or algae, with an extendible, jaw-like structure.
Some polychaetes dip into the substrate with feeding tentacles, scoop up some
muck, and draw it into their mouths to digest any edible particles.
Although many marine polychaetes reproduce asexually, all of the freshwater
species reproduce sexually. Most polychaetes have separate sexes, but some crawling
and swimming species are hermaphroditic (individuals bear both male and
female reproductive organs). A free-swimming larval stage is typical of marine
forms, but is absent in all freshwater species.
In the Arctic, individuals of Marenzelleria wireni, Chone sp., and Manayunkia speciosa have occasionally been found in tundra lakes. M. wireni is a highly adaptable species that can tolerate a wide range of conditions. It is found in both fresh and marine waters, although it usually inhabits the estuaries of rivers, where the water is not as salty. It can also tolerate a wide range of oxygen levels, even surviving without any oxygen at all! Chone sp. and Manayunkia speciosa are more restricted to freshwater habitats, although there is some speculation that they descended from marine species that entered the waters of North America in response to flooding of the land during the last glaciation. All three arctic freshwater polychaetes are widespread south of the Arctic.