The reproductive biology of Lyonsia hyalina (Conrad, 1831) (Mollusca: Bivalvia: Anomalodesmata): Ultrastructural aspects of spermatogenesis and oogenesis

The reproductive biology of the simultaneously hermaphroditic anomalodesmatid bivalve Lyonsia hyalina (Conrad, 1831) was examined. Transmission electron and light microscopy was used to study spermatogenesis and oogenesis in this organism.;This is only the second time oogenesis in a member of the bivalve subclass Anomalodesmata (i.e., L. hyalina) has been examined. The oocytes are similar in size to most other anomalodesmatids, though generally larger than in other shallow-water marine bivalve species. Cortical granules are absent in this species, thus the mechanism that prevents polyspermy remains undetermined.;Vitellogenic oocytes contain structures resembling poorly developed annulate lamellae which provides insight into this little understood organelle. This structure is apparently involved in the manufacture of protein yolk and the vitelline coat, although exogenous sources may also exist. Follicular cells grow around previtellogenic oocytes but become restricted to the thin stalk of late stage vitellogenic oocytes. Membrane degradation often occurs between follicular cells and oocytes, thus providing a mechanism through which substances can be transferred.;This species produces ect-aquasperm which is composed of a compact head, midpiece and long tail containing a flagellum. The midpiece has five mitochondria, a distal centriole (which acts as the flagellar basal body), a proximal centriole and a highly unusual acrosome. The acrosome develops during spermiogenesis and migrates to the posterior region of the spermatid midpiece. This acrosomal movement is unique to the bivalve subclass Anomalodesmata. Non-germinal cells are present in the testes and may provide nutrition to the developing sperm.