ULTRASTRUCTURE OF SPERMIOGENESIS AND SPERMATOZOA IN DIURODRILUS-SUBTERRANEUS (POLYCHAETA, DIURODRILIDAE)

Spermiogenesis in the polychaete species Diurodrilus subterraneus may be divided into six stages. These stages, as well as the ultrastructur e of the mature spermatozoa, are described based on TEM studies. The s permatozoa are unusual in having a very large acrosome followed by a r egion containing the nucleus and several ovoid mitochondria. A seconda ry acrosomal membrane forms a manchette around the nucleus and mitocho ndria. In this region, the plasma membrane is modified, with many smal l, mushroom-shaped cytoplasmic processes, each including filaments. Th e flagellum may be divided into three sequential regions; the longest, middle one is covered by a helically arranged mucous coat. Spermatozo a of the type described here are unknown among polychaetes but show ce rtain superficial resemblances to those in oligochaetes. The resemblan ce of the mushroom-shaped bodies to spermatozoal microvilli in certain gnathostomulids is discussed. The phylogenetic relationships of Diuro drilidae are considered on the basis of this new information.