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Summary
The keyhole limpet Fissurella crassa is a common archaeogastropod species occurring in the rocky intertidal zone along the entire Chilean coastline of South America. This study presents results of microscopic observations on female germ cell maturation required for recognition of fertility periods within its reproductive cycle. Sixty female specimens of over 45 mm in length were obtained for observation at Caleta Montemar (V Region, Chile) in August, October, and December 1997, and in February and April 1998. Gonadal tissue sections were prepared using current histological techniques for observations with light, transmission electron, and confocal laser microscopy. Four sequential stages of oocyte maturity are described, ranging from early oocyte development to oocytes at ovulation. Early and advanced germinal lines were recognized within the ovary structure. Cell stages were identified and described based on the predominant cell type present in samples collected during the study period. Mature oocytes (n = 150) obtained from five females were 317.04 ± 31.36 μm in diameter, while immature oocytes lacking the gelatinous layer measured approximately 229 μm. The oocyte covering begins as a vitelline coat, proceeding to a translucent gel layer with fine, broadly distributed microvilli structures; the oocytes then develop a third peripheral, ribbon-like structure formed of light-density fibrillar material, followed filially by a dense laminar coat, the chorion. The presence of a complex and well-defined pore (micropyle) was noted. This species exhibited continuous reproduction with partial spawning, with a proportion of mature individuals present in the population throughout the year. The present results provide information for future reproductive investigations on this species, which is a commercially valuable natural resource, and has potential for artificial culture and use in biotechnology assays.