Ultrastructural organization and development of male copulatory apparatus in Microsomacanthus sp (Cestoda, Cyclophyllidea)

Morphogenesis of the male copulatory apparatus in Microsomacanthus sp. begins from the aggregation of weakly differentiated cells, which form a three-layered anlage for a short time period. Each layer of the anlage is differentiated into the certain structure of the copulatory apparatus. Cells of the internal layer form cylindrical epithelium. The second layer consists of densely packed cells. The third layer is composed of chaotically located undifferentiated cells and nervous elements. The next stage of morphogenesis is characterized by the development of specialized contacts between epithelial cells. Apical parts of epithelial cells are destroyed forming a cavity in the reproductive channel. Then epithelial cells join into a syncytium, from which the nuclei eliminate. After embedding of the new population of undifferentiated cells into the epithelium layer, epithelium nuclei turn to be in the formed cirrus bag. Filamentous and blade-like microtriches are formed on the apical epithelial surface. Prostatic glands in Microsomacanthus sp. are absent. Muscular cells from the second anlage layer produce numerous cytoplasmic processes that fill the whole volume of the cirrus bag. An supplementary layer of longitudinal muscles is formed under basal matrix of epithelium. A thick layer of longitudinal muscles, which separates the copulatory apparatus from parenchyma cells is differentiated on the external side of the cirrus bag composed of muscular cells of the third layer. A thick basal plate develops between the second and third layers of the reproductive anlage. An additional layer of ring muscles is formed between the thick plate and longitudinal muscular fibers at the final stage of morphogenesis. The obtained and literature results on the ultrastructural organization and development of the copulatory apparatus are compared.