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(Poly = many, Chaeta = bristle) are the most diverse and most speciose group of the Annelida containing over 5,500 species. They are predominantly marine animals and are divided ecologically into the Errantia and the Sedentaria depending on whether or not they live sedentary lives in holes or live more active lives. We now know that this is not a taxonomically valid classification but it is useful as it divides the class in two in terms of the number of families each group contains. The Errantia have well developed heads and complex parapodia (paddles)that they can use for swimming. They are often dorsoventrally flattened.
Most polychaetes are gonochoristic (meaning they are either male or female), however some are sequential hermaphrodites (meaning they are one sex first and then change to being the other sex). Reproduction is often accompanied by the production of special modified reproductive segments which may, or may not, become independent of the parent worm before mating. These segments are destroyed or die during or immediately after they have released their gametes (sperm and ova) (11).
Most polychaetes are gonochoristic (meaning they are either male or female), however some are sequential hermaphrodites (meaning they are one sex first and then change to being the other sex). Reproduction is often accompanied by the production of special modified reproductive segments which may, or may not, become independent of the parent worm before mating. These segments are destroyed or die during or immediately after they have released their gametes (sperm and ova) (11).