Histological Description of Oogenesis in Chiton virgulatus (Mollusca: Polyplacophora)

Abstract

This paper describes the oogenesis of Chiton virgulatus, based on histological observations under transmission and scanning electron microscopy. Three oocyte types were identified: i) previtellogenic oocytes with a mean diameter of 50±20.5 mm, surrounded by elongated follicular cells of approximately 5 μ, ii) immature vitellogenic oocytes with a mean diameter of 113±15.3 mm and small cytoplasmic projections denoting the onset of the oocyte hull development; adjacent to each projection are pores approximately 0.7 μ in diameter, and iii) mature vitellogenic oocytes with a mean diameter of 146±24.8 mm; the oocyte cytoplasmic projections grow and its apical zone becomes trident-shaped; follicular cells adopt a bulbous shape due to the growth of the elongation and can reach up to 20 μ in length. The morphology and ultrastructure of the projections of the mature vitellogenic oocyte, as well as the size of pores at their base, are specific to C. virgulatus; therefore, these features could be used in taxonomic or fertilization studies.