Ultrastructural aspects of spermiogenesis of Temnocephala sp (Turbellaria,Rhabdocoela), ectoparasite of Dilocarcinus septemdentatus Herbst, 1783 (Crustacea, Decapoda)

Spermiogenesis and sperm cell of Temnocephala sp. were studied by light mic roscope, transmission and scanning electron microscope. The beginning of sp ermiogenesis involves formation of a zone of differentiation, giving rise t o two free flagella of the 9 + '1' flatworm pattern that grow in opposite d irections. Elongation of the spermatid takes place, along with reduction of nucleus volume. Then, the flagella rotate and emerge adjacent to one anoth er but perpendicular to the cell shaft. The mature spermatozoon is filiform , presenting an anterior thin region, a long sperm body, subterminal short flagella and a posterior tapered end. A thread-like nucleus is present thro ugh all the length of the sperm shaft, where we can also observe several sm all mitochondria and a large number of dense granules. Longitudinally linin g the perimeter of the sperm body there are rows of parallel slightly spira l singlets of microtubules, that overlap in a small extension. Ultrastructu re of the spermiogenesis and spermatozoon of Temnocephala sp. is similar to which occurs in other rhabdocoels, sometimes showing common features with the Cyclophyllidea, an order of the Cestoda.