The Spermatozoon of Capilloventer Australis and the Systematic Position of the Capilloventridae (Annelida: Oligochaeta)

Abstract

The spermatozoon and spermiogenesis of Capilloventer australis, an oligochaete annelid belonging to the family Capilloventridae, were examined with the aim of supplying further elements for the discussion of the phylogenetic position of the family. Capilloventer australis has a typical oligochaete spermatozoon, with an acrosome tube, mitochondria between the nucleus and flagellum, and a basal cylinder inside the basal body. The acrosome is plesiomorphic, with many characters in common with the Enchytraeidae. The nucleus is twisted, as that of most microdriles, 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 features of spermiogenesis, including the acute angle between the nuclear and flagellar axes, are probably plesiomorphic. The spermatological study here presented supports a basal position for the Capilloventridae among the oligochaetes.