The spermathecal epithelium, sperm and their interactions in the hermaphroditic land snail Arianta arbustorum (Pulmonata, Stylommatophora)

Previous investigations showed that in Arianta arbustorum incoming sperm ar e not equally distributed among all tubules of the sperm storage organ, the spermatheca, and it has been assumed that the sperm recipient might influe nce paternity after multiple mating. Understanding postmating sexual select ion requires understandings the function of the genitalia. Against this bac kground we analyse the ultrastructure of the spermathecal epithelium, give a brief description of the sperm morphology and describe the sperm-epitheli um interactions. The epithelium of the spermatheca, which consists of up to nine blind tubules originating from a common duct, is a monolayer composed of a single cell type. Only the density of the ciliation increases along t he tubules and the common duct. In addition, the cilia of the latter are mo re than 50% longer than those in the tubules. These long and densely arrang ed cilia not only prevent autosperm from getting into the spermatheca, but may also be responsible for sorting sperm in the spermatheca allowing the r ecipient to store sperm from different partners separately. The most peculi ar characteristics of the epithelium are the wide intercellular spaces at t he base continuing apically into narrow channels used for extracellular tra nsport. Below apical junctions, the cells adhere to each other through inte rdigitations, which form an extensive labyrinth at the base and rest on the basement membrane. Rough endoplasmic reticulum and Golgi complexes are mai nly found in the vicinity of the basally positioned nucleus. A large vacuol e Lies above the nucleus and the apical portion of the cytoplasm is densely populated with mitochondria. Vesicles of various sizes are also found main ly in the apical region. The spermatozoa stored in the hermaphrodite duct p rior to transfer are characterised by an acrosome forming an angle of 90 de grees with the longitudinal axis of the nucleus and vesicles of undefined s hape in the terminal end of the flagellum. In the spermatheca the spermatoz oa lose their perinuclear sheath and the acrosome is almost in line with th e longitudinal axis of the sperm. This process is interpreted as capacitati on. In the spermatheca, the capacitated spermatozoa are in close contact wi th the epithelial cells. However, an exchange of substances was not observe d. It is assumed that the epithelium provides the environment for sperm qui escence rather than nutritives.