Unusual features of sperm ultrastructure in the Musk shrew <i>Suncus murinus</i>

Abstract

The spermatozoon of the Musk shrew Suncus murinus displays unusual fine anatomical features. In the head, the equatorial segment of the acrosome is recessed within a waist in the sperm nucleus in a way that could afford some protection for this fusogenic region, perhaps during penetration of the egg vestments. The perinuclear material has distinctive inner and outer regions, the latter being arranged as a series of coxcomblike spikes. These structures in Suncus could serve to anchor its characteristically giant acrosome to the sperm nucleus. In the tail, small aggregations of electron dense material appear against some centriolar triplets and also, proximally, against some axonemal doublets. In the midpiece, prominent satellite material aggregates proximally over the inner border of the dense fibers. More distally, the material maintains a close relationship with and primarily lies between the corresponding axonemal doublets and dense fibers 5 and 6, the latter being positioned asymmetrically in relation to the remaining dense fibers.