Light and electron microscopic study on vitellogenesis of the caryophyllidean cestode Monobothrioides chalmersius (Woodland, 1924) Hunter, 1930 (Lytocestidae) from the catfish Clarias gariepinus

Transmission electron microscopy (TEM) has been applied for the first time to study vitellogenesis in the caryophyllidean tapeworm Monobothrioides chalmersius (Woodland, 1924) Hunter, 1930 from the catfish Clarias gariepinus inhabiting Nile Delta water in Egypt. During development of vitellocytes, cell size and nuclear surface are increased. Meanwhile, parallel cisternae of granular endoplasmic reticulum (GER) and Golgi complexes develop, but the nucleo-cytoplasmic ratio is restored, shell-globules (vitelline granules) are formed, small shell-granules fuse into larger shell-globules and large shell-globules fuse into larger shell-globule clusters, cytoplasmic and nuclear glycogen accumulate. Mature vitellocytes of M. chalmersius contain five kinds of vitelline material: shell globules clusters (vitelline granules), glycogen, few probably lipid droplets, many peripheral translucent vesicles and electron-dense vesicles. The interstitial tissue consists of cells from which many cytoplasmic processes extend to be in close contact with maturing and mature vitellocytes. The cytoplasm of the interstitial cells contains some electron-dense vesicles. The possible function of the interstitial cells inclusions is discussed. The vitellogenesis of M. chalmersius follows the basic pattern of the process in caryophyllidean cestodes but some differences were recorded particularly in the ultrastructure of the mature vitellocytes and interstitial tissue. Vitellogenesis and ultrastructure of the mature vitellocytes and interstitial tissue of M. chalmersius are compared particularly with those in other monozoic cestodes.