Spermatid differentiation and the morphology of mature spermatozoa in Nucella crassilabrum, a muricid snail, was investigated. Five phases of spermiogenesis considering the polarization of organelles, nuclear elongation and chromatin condensation are described. Characteristics observed are compared to those of other muricaceans gastropods. The comparison of the proportional size of the different sperm segments (head, middle- and principal piece) between these species, is emphasized.