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Abstract
A survey of the structure and variety of the nephridia in the subclass Oligochaeta is presented. The most diversified forms are discernible in the families of Megadrile earthworms Two main types can be differentiated: holonephridia and meronephridia. Both types can be exonephric when they penetrate the body-wall and open to the exterior. However, in the meronephridia, the ducts can open also into the intestine; in this case, it is called enteronephric. The nephridia in the family of Enchytraeidae are holo-exonephric; namely, they always have a ciliated funnel connected to a coiled duct much folded and embedded in a compact elongated body covered by a layer of peritoneum and through an efferent duct open to the exterior in the next segment. The shape of this organ, the structure and the ratio of pre- and post-septale parts, and the origin of the efferent duct can be generic or specific in character. The number of nephridia in pre-clitellar segments may contribute to identification of the species, but our knowledge on these characteristics is insufficient; therefore, it would be very useful to record these traits in all species descriptions.