Parvidrilus strayeri, a new genus and species, an enigmatic interstitial clitellate from underground waters in Alabama

An exceedingly small oligochaete, Parvidrilus strayeri, a new genus and spe cies, is described from a streambed in northern Alabama, U.S.A. The species is up to 1.4 mm long (with up to 33 segments) and has several unusual feat ures. In ovigerous specimens, a clitellum is developed as a pair of lateral rows of a few, large, swollen epidermal cells in segments (IX-) X-XII (-XI II, -XIV). Chaetae are absent from segment II. Otherwise, in the anterior p art of the body, there are long hair chaetae as well as small crotchet chae tae in both dorsal and ventral bundles. Furthermore, the chaetal bundles ar e situated posteriorly in each segment. It is unclear whether gonads are pa ired or unpaired; testes (testis?) are in segment XI, ovaries (ovary?) in X II. The other reproductive organs include a U-shaped muscular 'genital body ' in segment and a V-shaped 'copulatory organ' in segments XII-XIII; the ex act nature and function of these structures are unknown. The genus is propo sed to be classified as the single member of Parvidrilidae, new family. It appears to be most closely related to two, largely Southern Hemisphere, aqu atic clitellate families, Capilloventridae and Phreodrilidae. A possible re lationship to the monotypic, South American taxon, Narapidae, is also discu ssed.