Sperm ultrastructure in two species of the marine snail family Olividae is examined. Euspermatozoa of both species are composed of a conical, membrane-bound acrosomal vesicle; an axial rod and a basal plate similar in both species; a solid and highly electron-dense nucleus; an elongate midpiece consisting of the axoneme sheathed by helical mitochondrial elements; an elongate glycogen piece; a double electron-dense ring at the junction of the midpiece and glycogen piece; and a free tail region. The slight narrowing in the acrosomal vesicle invagination is situated in different levels between Olivancillaria deshayesiana and Olivancillaria carcellesi. This morphology could be considered as a specific character. The length of the nucleus in O. carcellesi and in O. deshayesiana is shorter than that of other neogastropods, and could be diagnostic at family level.
