ULTRASTRUCTURE OF SPERMATOGENESIS OF ATRIASTER HETERODUS (PLATYHELMINTHES, MONOGENEA, POLYOPISTHOCOTYLEA)

The development of spermatozoa in the Polyopisthocotylea Atriaster het erodus was studied by transmission electron microscopy. Spermatogonia were undifferentiated, with irregular nuclei and little cytoplasm. Pri mary spermatocytes had sparse chromatin and typical synaptonemal compl exes. The nuclear chromatin of secondary spermatocytes was in parches along the nuclear envelope and throughout the nucleoplasm. The complet e process of fusion of the early spermatids to a common cytoplasmic ma ss forming a rosette was elucidated. Nuclei migrated to the center of the mass and changed from round to lamellar or tubular in shape. At th e borders of the common cytoplasmic mass, the irregular zones of diffe rentiation had microtubules, mitochondria, nuclei, centrioles, and int ercentriolar bodies that give rise to 2 flagella. The spermatozoa pres ented a continuous row of cortical microtubules surrounding 2 parallel s axonemes of the 9+1 type.