Ultrastructure of spermiogenesis and the spermatozoon of Mesocestoides litteratus (Cestoda, Mesocestoididae).

This paper constitutes the first ultrastructural study of spermiogenesis and the spermatozoon of a cestode belonging to the family Mesocestoididae, Mesocestoides litteratus. Spermiogenesis in M. litteratus is characterised by a flagellar rotation and a proximodistal fusion. The zone of differentiation presents striated roots associated with the centrioles and also an intercentriolar body. The most interesting ultrastructural feature found in the mature spermatozoon of M. litteratus is the presence of parallel cortical microtubules. The spermatozoon also exhibits a single crest-like body and granules of glycogen. The pattern of spermiogenesis and the parallel position of cortical microtubules reveal the lack of concordance between M. litteratus and cyclophyllidean species studied to date in spermiogenesis and in the ultrastructural organisation of spermatozoon. This study provides new spermatological data and calls into question the validity of the current systematic position of mesocestoidids.