Sperm morphology and spermiogenesis in the methane-seep mollusc Bathynerita naticoidea (Gastropoda: Neritacea) from the Louisiana slope

Bathynerita nalicoidea, a bathyal neritid prosobranch endemic to oil and gas seeps in the Gulf of Mexico, produces filiform eusperms ~90 µm long. The eusperm is of the introsperm type, typical of invertebrates with internal fertilization, and they are similar in structure to those of shallow-water neritimorph taxa. The head of the sperm is ~26 µm long and consists of an elongate tubular nucleus (˜24 µm long X 0.2 µm diameter) and acrosome (~2 µm long), which sits on a subacrosomal plate.