전자저널 > 전자저널 > Ultrastructural Description on Oogenesis of the Melania Snail, Semisulcospira libertina libertina (Gastropoda: Pleuroceridae)

Ultrastructural Description on Oogenesis of the Melania Snail, Semisulcospira libertina libertina (Gastropoda: Pleuroceridae)

Eun Kyoung Kim and Jung Sick Lee1

Medvill Co., Ltd., Gasan-dong, Geumcheon-gu, Seoul 153-801, Korea 1Department of Aqualife Medicine, Chonnam National University, Yeosu 550-749, Korea

The ultrastructural changes in germ cells during oogenesis of the melania snail, Semisulcospira libertina libertina have been investigated by light and electron microscopy. The ovary is located on the surface of the hepatopancreas in the spiral posterior region. The ovary exhibited greenish color in the gonadal mature season. The ovary was composed of a number of oogenic follicles. Oogenesis was divided into five stages with histological features: (1) oogonia, (2) previtellogenic, (3) initial vitellogenic, (4) active vitellogenic, and (5) mature stages. Oogonia were oval in shape, 4-6 μm in diameter, and had a large nucleus. Previtellogenic oocytes were about 20 μm in diameter and the cytoplasm reacted with hematoxylin in H-E satin. Initial vitellogenic stage, oocytes were 60-80 μm in diameter, and small yolk granules of low electron density are scattered in the cytoplasm. Oocytes in the initial vitellogenic stage were connected with ovarian follicle by egg stalk. Active vitellogenic oocyte were 100-120 μm in diameter. Electron density, size and quantity of yolk granules that are distributed in the cytoplasm have increased from the previous stage. Result of TEM observations, the oocyte contains well-developed Golgi complex, endoplasmic reticula and tubular mitochondria in the cytoplasm. Cytoplasm of mature oocyte was filled with proteinaceous yolk globules of high electron density. In this stage, the length of microvilli in the egg envelope was approximately 1.1 μm.

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