THE SPERMATOZOON OF CAPILLOVENTER AUSTRALIS AND THE SYSTEMATIC POSITION OF THE CAPILLOVENTRIDAE (ANNELIDA, OLIGOCHAETA)

The spermatozoon and spermiogenesis of Capilloventer australis, an oli gochaete annelid belonging to the family Capilloventridae, were examin ed with the aim of supplying further elements for the discussion of th e phylogenetic position of the family. Capilloventer australis has a t ypical oligochaete spermatozoon, with an acrosome tube, mitochondria b etween the nucleus and flagellum, and a basal cylinder inside the basa l body. The acrosome is plesiomorphic, with many characters in common with the Enchytraeidae. The nucleus is twisted, as that of most microd riles, but the middle piece is highly apomorphic in being formed by 11 mitochondria that are not in the usual radial arrangement. The basal cylinder is long and similar to that of the Enchytraeidae. Some featur es of spermiogenesis, including the acute angle between the nuclear an d flagellar axes, are probably plesiomorphic. The spermatological stud y here presented supports a basal position for the Capilloventridae am ong the oligochaetes.