Clitellum not present as a definite organ, as in Oligochaeta.
Clitellum 37 always present, extendin over two (many limicolous forms) to forty-five seg ments (Alma).
The clitellum consists of a thickening of the epidermis, and is of two forms among the Oligochaeta.
It is therefore obviously much thicker than the clitellum in the limicolous forms. The position of the clitellum, which is universal in occurrence, varies much as does the number of component segments.
There are a clitellum and sperm ducts which though like nephridia have a larger funnel and a less complexly wound duct.
Nerve cord lies in coelom; brain in first segment or prostomium in many forms. Clitellum generally only two or three segments and more anterior in position than in Terricolae.
Clitellum commonly extensive and more posterior in position than in other groups.
The appendages of the body are reduced to branchiae, present in certain forms. A clitellum is present.