Ultrastructure of spermiogenesis and spermatozoa ofPolylabroides australis(Platyhelminthes, Monogenea, Polyopisthocotylea, Microcotyudae)

Abstract

Testis follicles are surrounded by a sheath and conlain several stages of spermatogenesis. Primary spermatocytes have large nuclei with a loose granular appearance and synaptonemal complexes, and their densely packed cell bodies are small and rich in mitochondria. Spermatids are joined to a central cytophore; their nuclei are at first spherical and located near the tips of the spermatids, later they elongate and coil. In each of the cytoplasmic protuberances (the of differentiation) in the periphery of the cytophore, two flagella, each with a cross-striated rootlet, grow out from basal bodies separated by an intercentriolar body, and later fuse in a proximo-distal direction with the median cytoplasmic process which has developed at the tip of the zone of differentiation. The zones of differentiation and the median cytoplasmic processes possess a row of peripheral microtubules. Mature sperm have a single row of peripheral microtubules that is incomplete in some parts of the sperm. Number of peripheral microtubules decreases towards both ends from about 55 in the principal region. One axoneme terminates before the other in the nuclear region, and nucleus and mitochondrion overlap only in the middle regions. The proximal end contains the axonemes, and the distal end the nucleus.