Fine structure of spermatogenesis in polyopisthocotylid monogeneans (Protomicrocotyle ivoriensis, Gastrocotyle sp.).

The development of spermatozoa in the polyopisthocotylean fish-gill flukes Protomicrocotyle ivoriensis and Gastrocotyle sp. was investigated by light and transmission electron microscopy. In both species the spermatogonia were undifferentiated cells, the cytoplasm of which contained numerous free ribosomes, and successive mitoses gave rise to primary spermatocytes, which are clearly identified by the presence of synaptonemal complexes in their nuclei. As compared with that of the spermatogonia, the cytoplasm of the primary spermatocytes contained an increased number of ribosomes. Golgi complexes were frequently seen in the spermatocytes of P. ivoriensis but not in Gastrocotyle sp. In P. ivoriensis the secondary spermatocytes were separated by interspaces between the irregularly shaped cell surfaces. In both species a syncytial mass of spermatids developed, which gave rise to 64 spermatozoa. Cross sections of the mature spermatozoa of both species revealed the presence of numerous submembranous microtubules and two axonemes showing a pattern of 9 doublet peripheral microtubules plus a central one. In contrast to microtubules plus a central one. In contrast to P. ivoriensis, in Gastrocotyle sp. the axonemes originated from different places at the axis of the spermatozoon. With respect to the other results obtained, the spermiogenesis and the fine structure of spermatozoa of both species studied were similar to previous findings in other polyopisthocotyleans.