Analytical studies of the ultrastructure and movement of the spermatozoa of freshwater triclads

Abstract

The spermatozoa in the testis of three species of triclad turbellarians showed slightly different morphologies from spermatozoa in the seminiferous tubule and ovovitelline duct, and we suggest these differences relate to maturation of the spermatozoa. Glycogen granules could be found in the flagella between the central core and the peripheral doublets of spermatozoa in the seminiferous tubule and ovovitelline duct but only rarely in spermatozoa in the testis, and connections between a third arm of the doublets and the flagellar membrane were detectable only in those spermatozoa in the ovovitelline duct and seminiferous tubule. The movement of spermatozoa also appeared to change with capacitation: spermatozoa isolated from the spermiducal vesicle swam with either the anterior process or the head leading; those within the ovovitelline duct appeared to move with the anterior process leading. The flagellum, with the so-called ‘9 + 1’ axonemal pattern, was observed to divide into nine branches toward its distal end; the central cylinder of the axoneme did not continue into the branches. An acrosome has not been observed in planarian spermatozoa. Rod-like structures and a dense mass lying in the anterior process and suspected of containing an acrosomal substance, could not be shown to produce acrosome-like proteolytic activity.