Ultrastructure of spermiogenesis and thespermatozoon of Mesocestoides litteratus (Cestoda,Mesocestoididae)

Abstract

This paper constitutes the first ultrastructural study of spermiogenesis and thespermatozoon of a cestode belonging to the family Mesocestoididae, Mesocestoides litteratus. Spermiogenesis in M. litteratus is characterised by a flagellar rotation and aproximodistal fusion. The zone of differentiation presents striated roots associated with thecentrioles and also an intercentriolar body. The most interesting ultrastructural feature found inthe mature spermatozoon of M. litteratus is the presence of parallel corticalmicrotubules. 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 ofconcordance between M. litteratus and cyclophyllidean species studied to date inspermiogenesis and in the ultrastructural organisation of spermatozoon. This study provides newspermatological data and calls into question the validity of the current systematic position ofmesocestoidids.