Ultrastructure of spermiogenesis and the spermatozoon of Sudarikovina taterae (Cestoda, Cyclophyllidea, Anoplocephalidae) intestinal parasite of Tatera gambiana (Rodentia, Gerbillidae)

The young spermatid of Sudarikovina taterae exhibits a nucleus with a partially condensed chromatin and a differentiation zone, bordered by cortical microtubules, delimited at the front by arched membranes and containing two centrioles. The latter are parallel to one another and linked together at their bases by electron-dense material. During spermiogenesis, one of the centrioles gives rise to a flagellum whereas the other disappears. Crested-like bodies lie outside the cortical microtubules and the nucleus migrates in the spermatid along the axoneme. At the end of spermiogenesis, the ring of arched membranes constricts and the old spermatid becomes detached from the residual cytoplasm. The S. taterae mature spermatozoon is filiform and tapered at both extremities. It exhibits an apical cone of electron-dense material and seven crested-like bodies 50 to 100 nm thick. The cortical microtubules run along the whole length of the spermatozoon. They are spiralized at their anterior extremities and straight over the rest of their length. The nucleus is a fine compact cord interposed between the axoneme and the cortical microtubules. The cytoplasm is slightly electron-dense in regions I and II of the gamete. In regions III, IV and V, it contains fine electron-dense granulations and patches of electron-lucent material. An electron-dense material located both between and under centrioles has not been observed before in a platyhelminth. Similarly, distinctive ultrastructural characters between centrioles and seven crested-like bodies have not been previously described in a cestode. Moreover, we report for the first time the existence of cortical microtubules spiralized only at their anterior extremities in a cestode from a mammal.