The data on the ultrastructure of spermatozoa and oocytes and their development in the marine tricladid Uteriporus vulgaris are described for the first time. The conservativeness of the spermatozoal morphology in Tricladida as one of the most advanced turbellarian orders is notified. In addition, some specific ultrastructural features of spermatids and oocytes in U. vulgaris are described
