The re-discovery of a tubificid originally described as Heterodrilus arenicolus, together with a study of the efferent ducts of Clitellio arenarius, has led to the merging of Heterodrilus in Clitellio. Clitellio subtilis seems to be very closely related to C. arenicolus. A new genus is erected to receive a second marine species discovered, like the first, in material from the Gulf of Mexico and the Atlantic seaboard off North Carolina, U.S.A.
