Ultrastructural aspects of spermatogenesis, testes, and vas deferens in the parthenogenetic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea), a carp parasite from Slovakia.

Spermatogenesis, testes, and vas deferens in the parthenogenetic monozoic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea) from Slovakia, parasitizing the carp Cyprinus carpio L., have been investigated by means of transmission electron microscopy for the first time. The present results show that helminths with parthenogenetic and normal reproduction may share some common spermatology features, e.g., dense cytoplasm of the peripherally localized spermatogonia or a rosette type of spermatogenesis. In contrast to tapeworms with normal reproduction, the most prominent ultrastructural characteristic of the spermatocytes of A. huronensis is fragmentation of their nuclei. This clear feature of cell degeneration might be a consequence of the aberrant first meiotic division. Peripheral cortical microtubules and a single centriole, indicators of the ongoing spermiogenesis, were observed only very rarely in the early spermatids. Characteristics of normal spermiogenesis, i.e., apical dense material in the zone of differentiation in early stages of spermiogenesis, flagellar rotation, and proximo-distal fusion, were never found in the present study. The testes follicles are surrounded by a thin cytoplasmic sheath underlined by a basal lamina. Vas deferens is lined by flat epithelium with numerous surface lamellae and cilia. Mature, functional spermatozoa were not observed in the vas deferens of A. huronensis from Slovakia.