ULTRASTRUCTURE OF SPERMIOGENESIS AND THE MATURE SPERMATOZOON OF TETRABOTHRIUS-EROSTRIS LOENNBERG, 1896 (CESTODA, TETRABOTHRIIDAE)

The spermiogenesis of Tetrabothrius erostris is characterized by tbe f ollowing events: formation of a differentiation zone containing 2 basa l bodies and a pair of rootlets; one of the basal bodies gives rise to a free flagellum, the other induces formation of a flagellar bud; rot ation at 90 degrees of the flagellum prior to its fusion with the midd le cytoplasmic process of the differentiation zone and partial rotatio n of the flagellar bud; penetration of the nucleus between the rootlet s and appearance of a spur-like protrusion in the differentiation zone ; elongation and twisting of the differentiation zone, resulting in tw isting of the peripheral microtubules and migration of the nucleus; fo rmation of a crested body; proximal densification of the spermatozoon prior to its detachment from the spermatid rosette. The mature spermat ozoon has a single axoneme of 9+''1'' type and twisted peripheral micr otubules. It consists of 3 portions: a proximal part with a crested bo dy, a middle region rich in beta-glycogen, and a distal part containin g the nucleus. The pattern of spermiogenesis resembles most closely th at in phyllobothriid tetraphyllideans, and probably reflects a relatio nship of the family Tetrabothriidae with this group.