Ultrastructural study of spermiogenesis and the spermatozoon in Catenotaenia pusilla, an intestinal parasite of Mus musculus

The ultrastructure of spermiogenesis and the mature spermatozoon in Catenot aenia pusilla (Cestoda: Catenotaeniidae) is described. Spermiogenesis is ch aracterized by the presence of a single axoneme which grows on the outside of a cytoplasmic extension at an angle of 45 degrees. Flagellar rotation an d proximodistal fusion are produced in this process. The centrioles lack st riated roots and an intercentriolar body. In the mature spermatozoon four d ifferent regions are described. The anterior extremity is capped by an apic al cone and presents two helical crest-like bodies of unequal length. The a xoneme, of the 9 + '1' pattern of the Trepaxonemata, presents a periaxonema l sheath. The cortical microtubules form a spiral pattern at an angle of ab out 40 degrees to the hypothetical spermatozoon axis. The nucleus is kidney - to horseshoe-shaped in cross section. Granules and proteinaceus walls are not observed in the spermatozoon of C. pusilla.