Description of Clitellata
Clitellata is a class of Annelid worms, characterized by having a clitellum - a collar that forms a reproductive cocoon during part of their life cycle. The clitellates comprise around 8,000 species. All clitellata are hermaphrodites. During reproduction, the clitellum secretes a coat which hardens. The worm then creeps out backward from the coat and deposits either fertilized zygotes or both ova and sperm into the coat, which is then packed into a cocoon. The zygotes then evolve further directly in the cocoon without passing through a larva stadium (as opposed to other annelids, e.g. polychaeta.) Description accessed from WikiPedia 3rd August 2008, and modified.
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