SPERMATOZOON STRUCTURE OF SOME NORTH-AMERICAN PROSOBRANCHS FROM THE FAMILIES LOTTIIDAE (PATELLOGASTROPODA) AND FISSURELLIDAE (ARCHAEOGASTROPODA)

The spermatozoa of four species of the patellogastropod family Lottiid ae (Lottia pelta, L. digitalis, L. strigatella, Tectura scutum) and on e species of the archaeogastropod family Fissurellidae (Diodora aspera ) were examined in 1990 using transmission electron microscopy. All ha ve primitive or ect-aquasperm, typical of invertebrates using external fertilization. Sperm of the lottiid limpets are characterized by a 5 to 9 mum-long head composed of a conical acrosome which constitutes > 50% of the head length, and a cylindrical nucleus. The acrosome of all species of lottiids is differentiated internally, and has a posterior invagination congruent-to 0.9 to 1 mum in depth, into which an elonga te acrosomal lobe protrudes. Between the posterior acrosomal lobe and the nucleus, the subacrosomal material is aggregated as a fibrous colu mn. The midpiece of the sperm has a ring of 4 to 5 spherical mitochond ria of congruent-to 0.6 mum diam, posterior to which is a collar of cy toplasm congruent-to 1 mum long, which sheaths the anterior portion of the axoneme. The size and morphology of the acrosome and large cytopl asmic collar clearly distinguish the spermatozoa of the Lottiidae from other families of Patellogastropoda. The sperm of D. aspera (Fissurel lidae) is typical of the family of archaeogastropod; the head has a le ngth to breadth ratio of 4:1, and the cylindrical nucleus is capped by a small acrosome, < 25 % of the total head length, which is deeply in vaginated.