Ultrastructure of the gametolytic gland and seminal receptacle in Hypselodoris messinensis (Gastropoda, Opisthobranchia).

ABSTRACT

The gametolytic gland of Hypselodoris messinensis is a voluminous globular structure that encloses a large mass of degenerative gametes, especially waste exogenous sperm. The epithelial cells of this organ show some features characteristic of secretory cells and probably release hydrolytic enzymes into the lumen. The amorphous material accumulated in the gametolytic gland does not appear to be reabsorbed by the lining epithelium. The seminal receptacle stores exogenous sperm received during copulation. The spermatozoa are oriented radially their heads are embedded in the epithelium and their tails are directed toward the center of the lumen. The epithelial cells of the seminal receptacle may synthesize certain substances that induce sperm activation and maintain them in adequate physiological conditions. However, they apparently do not perform an important function of sperm nourishment. The nuclear chromatin of spermatozoa stored in the seminal receptacle is not homogeneously condensed, but forms longitudinal filaments. The significance of this phenomenon, which also occurs in other nudibranchs, remains to be understod.