Ultra structural study of the Embryonic Development in the Intrauterine Eggs of Acanthostomum (atrophocaecum) aswaninesis Wannas, 1977 (Digenea, Acanthostomatidae) with evidence of early miracidium development

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 Intrauterine embryonic development of the eggs of Acanthostomum (atrophocaecum) aswaninesis was investigated by transmission electron microscopy. The study revealed the successive stages of embryonic development of the eggs. The proximal uterus contains unembryonated eggs and eggs with early embryos while the distal regions of the uterus were occupied with eggs containing fully developed embryos, each was composed of a fertilized oocyte and few vitelline cells; which were fused forming the vitelline syncytium that characterized the early embryonated eggs. With egg development, the eggshell progressively thickened with the appearance of the operculum after shell formation at the narrower pole of the eggshell surface. Three types of differentiated blastomeres are formed as a result of the continued cleavage divisions; macromeres, mesomeres and micromeres, with nuclei of different shapes and sizes. They occupy different places within the embryo. As a result of the following cleavage divisions, early degeneration or apoptosis of some micromeres take place. Numerous fully developed cilia are easily visible around the differentiated embryo (miracidium) of the advanced stages. The cilia have a typical 9+2 (nine peripheral and two central) arrangement of microtubules. The germinative cells of miracidia have easily appeared in the medioposterior parts of their ciliated larvae. The results of the present study were compared with those previously reported for other parasitic Platyhelminthes.  

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