A comparison of the structure of the spermatozoa and spermatogenesis of 16 species of patellid limpet (Mollusca: Gastropoda: Archaeogastropoda).

Abstract

Light and transmission electron microscopy of the spermatozoa and spermatogenesis of 16 species (in three genera, Patella, Helcion, Cellana) of patellid limpet have shown that head lengths of the sperm range from 3 to 13 μm, and each species has a sperm with a unique morphology, indicating that the spermatozoa can be used as a taxonomic character. Although spermatozoon structure is species specific, five types can be recognized, based on the size, shape, and structure of the nucleus and acrosome. The occurrence of five morphological types of sperm, one of which (Cellana capensis) is particularly different from other patellids, suggests that the taxonomy of the family Patellidae be re-examined. The morphological changes that occur during spermatogenesis are very similar in all species, although two patterns of chromatin condensation are found. Those species with sperm that have short squat nuclei (length:breadth < 3.5:1) have a granular pattern of condensation. Species with sperm that have more elongate nuclei (length:breadth > 5:1) have an initial granular phase followed by the formation of chromatin fibrils. These fibrils become organized along the long axis of the elongating nucleus. The absence of a manchette suggests that nuclear elongation is brought about from within the nucleus.