A clitellum is part of the reproductive system of an annelid (a worm with small rings or segments). The clitellum is a thick, saddle-like, ring found in the epidermis (skin) of the worm. To form a cocoon for its eggs, the clitellum secretes a viscous fluid. This organ is used in sexual reproduction of some annelids. The clitellum becomes apparent in mature annelids and may be hard to visually locate in younger annelids. Its color is usually slightly lighter than that of the body of the annelid.
Mitchell, Anne P. All about segmented worms-phylum annelida.Retrieved
Online August 1, 2008. http://www.allaboutworms.com/segmented-worms- phylum-annelida
The Free Dictionary. August 1, 2008. http://www.thefreedictionary.com/clitellum