AB prepress abstract  -  doi: 10.3354/ab00046

ABSTRACT: Ultrastructural features of the ovary and oogenesis have been examined in the tropical abalone Haliotis varia with the help of transmission electron microscopy. Based on the ultrastructure, the female germ cells were divided into five stages; oogonia, pre-vitellogenic, early vitellogenic, late vitellogenic and mature oocytes. Oogonia were supported by follicle cells that lined up the inner walls of the ovary. Vitellogenesis in H. varia commenced at about 50μm oocyte diameter, with major contribution by autosynthetic pathway. Lipid as well as protein yolk granules, measuring 2.3 ± 0.2 μm and 2.5 ± 0.3 μm, respectively, were observed in late vitellogenic and mature oocytes. Many membrane specializations involved in the synthesis of lipid yolk components inside the oocyte cytoplasm. Vitellogenic oocytes were surrounded by a vitelline coat consisting of a single layer of about 2.3 μm thickness. Numerous microvilli were embedded in the vitelline envelope. Cytoplasmic inclusions such as cortical granules, lipid droplets, mitochondria and yolk granules constituted the fundamental components of the mature oocyte. The cortical granules were found to be arranged beneath the oolemma at the cortex of the oocyte. Oocyte degeneration in H. varia was observed in all the stages of oocyte development except in oogonial cells and pre-vitellogenic oocytes.