Spermiogenesis and sperm ultrastructure of Diphterostomum brusinae (Digenea, Zoogonidae), a parasite of Diplodus annularis (Pisces, Teleostei).

This paper constitutes the first ultrastructural study of spermiogenesis and the spermatozoon of a Digenea belonging to the family Zoogonidae, Diphterostomum brusinae. Spermiogenesis follows the general pattern found in the digeneans. It begins with the formation of a differentiation zone in the spermatid. The two centrioles give rise to flagella. These two flagella undergo a rotation of 90 degrees and fuse with the median cytoplasmic process. The proximo-distal fusion occurs at the level of attachment zones. The mature spermatozoon of D. brusinae presents all the features found in the digeneans gametes: two axonemes, mitochondrion, nucleus and two bundles of parallel cortical microtubules. Nevertheless, several characteristics distinguish the spermatozoon of D. brusinae from other digeneans, in particular the external ornamentations of the plasma membrane and the anterior and posterior extremities. The description of the ultrastructural features of reproduction in this species would contribute to the understanding of the phylogenetic relationships in the Zoogonidae family.