The current investigation is concerning with the studying of the histology and ultrastructure of the digestive gland of the freshwater bivalve Caelatura parreyssi using light and transmission electron microscopes. This study was carried out on ten healthy clams, which were collected from the River Nile in Egypt. The specimens were dissected and small pieces of the digestive gland were selected out and processed for histological and ultrastructural examinations. The histological results revealed that the digestive gland of C. parreyssi is composed of numerous tubules, which are separated by connective tissues. Three types of cells were identified lined the digestive tubules; the digestive, excretory and crypt cells. Concerning the ultrastructural examination, digestive vesicles of different stages were seen that represent the characteristic features of the digestive cells. Excretory cells were distinguished by their excretory granules, whereas crypt cells showed spherules of calcium, which areconsidered also as characteristic ultrastructural feature. In conclusion, the present study revealed that the digestive gland of the freshwater bivalve Cealatura parreyssi has many functions covering the digestion, secretion and excretion processes. Moreover, it has a detoxification role.

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Oogenesis Histology UltrastructureThe present study was carried out to describe the ovary and oogenesis in the freshwater bivalve Caelatura parreyssi from histological and ultrastructural points of view. Ten adult healthy clams collected from the River Nile were used in this study. The specimens were dissected and gonads were obtained and processed for histological and ultrastructural examination. Histologically, the ovary of C. parreyssi is composed of numerous of follicles which are connected together by connective tissue. Each follicle contains different stages of developing oocytes; oogonia, previtellogenic oocytes, vitellogenic oocytes and postvitellogenic oocytes (mature oocytes). At ultrastructural level, stages of female gametogenesis were examined; the process of oocytes formation and yolk deposition were described in successive stages of oogenesis. The structure and function of auxiliary cells and follicle cells in ovarian follicles during vitellogenesis were discussed. In conclusion, this study showed that the follicle cells play an important role during oogenesis but probably are not the major source of yolk precursors. The vesicular connective tissue is probably the main source of nutrients for vitellogenesis. The auxiliary cells appear to play an integrate role in the development of the oocytes as their functions can permit a transfer of precursors necessary to vitelogenesis.

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