On some ultrastructural features of the reproductive system of the monogenean parasite Macrogyrodactylus congolensis from Clarias gariepinus inhabiting the River Nile in Egypt.

Some organs of the reproductive system of the protogynous monogenean skin parasite Macrogyrodactylus congolensis (Prudhoe, 1957) Yamaguti, 1963 have been studied using transmission electron microscopy. The vesicula seminalis is enclosed by a prominent layer of circular muscle fibres and has inner syncytial protrusions. The penis bulb is a highly muscular organ with prominent radial and circular muscle fibres, a gutter-shaped large spine and 16 small spines. Two syncytial male accessory glands, and a single reservoir for male accessory secretion were identified. The secretory bodies in the male accessory glands and male accessory reservoir have a unique structure. A large oocyte is situated in a chamber, previously referred to as the "ootype" or "egg-cell-forming region" (ECFR), which also contains one or two small undifferentiated cells and vacuolated tissue. Mature spermatozoa were abundant in the receptaculum seminis and dispersed in the vacuolated tissue in the ECFR and appeared to be attached to the membrane of the large oocyte. Mature spermatozoa were also seen in the parenchymal tissue near the chamber containing embryos and even in the tissues of the embryo.

Ultrastructure of the digestive system and experimental study of feeding in the monogenean skin and fin parasite Macrogyrodactylus congolensis.

In the present study, transmission electron microscopy (TEM) has been used to study the ultrastructure of the digestive system, namely the pharynx, oesophageal glands and intestine, of the monogenean skin and fin parasite Macrogyrodactylus congolensis. The pharynx consists of an anterior highly muscular region and a posterior mainly glandular syncytial region. The anterior region is provided with six pharyngeal papillae, the centre of each of which is occupied by electron dense secretory bodies, identical with those in the posterior region of the pharynx. The intestine has an uninterrupted syncytial gastrodermis and the luminal surface is provided with many unbranched lamellae. The intestine of living specimens contains large and small granules which give it a reddish brown colour. Large particles, presumed to be lipid droplets, and small granules, presumed to be melanin granules, were found in the gastrodermis and in the intestinal lumen. Parasites were induced to feed and then preserved for TEM at the following intervals: just after feeding, 30 min after feeding, 1 h 30 min after feeding and 2 h after feeding. The specimens were then processed for TEM and sections cut through the intestine of each specimen were examined with the transmission electron microscope. Three types of vacuoles (V1, V2, V3) were detected in the gastrodermis. Vacuoles V1 have thick walls and are likely to be endocytotic, enclosing luminal contents at the surface of the gastrodermis. V2 vacuoles may be lysosomes that fuse with V1 vacuoles. V3 vacuoles may serve to dispose of residual digestive material into the lumen.

Neuromusculature of Gyrodactylus rysavyi, a monogenean gill and skin parasite of the catfish Clarias gariepinus.

Phalloidin fluorescence technique, enzyme cytochemistry and immunocytochemistry in conjunction with confocal scanning laser microscopy were used for the first time to describe the nervous and muscle systems of the viviparous monogenean parasite, Gyrodactylus rysavyi inhabiting the gills and skin of the Nile catfish Clarias gariepinus. The body wall muscles are composed of an outer layer of circular fibres, an intermediate layer of paired longitudinal fibres and an inner layer of well-spaced bands of diagonal fibres arranged in two crossed directions. The musculature of the pharynx, intestine, reproductive tract and the most prominent muscles of the haptor were also described. Two characteristic muscular pads were found lying in the anterior region of the haptor in close contact with the hamuli. To each one of these pads, a group of ventral extrinsic muscles was connected. The role of this ventral extrinsic muscle in the body movement was discussed. The mechanism operating the marginal hooklets was also discussed. The central nervous system (CNS) consists of paired cerebral ganglia from which three pairs of longitudinal ventral, lateral and dorsal nerve cords arise. The nerve cords are connected at intervals by many transverse connectives. The CNS is better developed ventrally than dorsally or laterally and it has the highest reactivity for all neuroactive substances examined. Both the central and the peripheral nervous system (PNS) are bilaterally symmetrical. Structural and functional correlates of the neuromusculature of the pharynx, haptor and reproductive tracts were explained. The results implicated acetylcholine, FMRFamide-related peptides (FaRPs) and serotonin in sensory and motor function. The results were compared with those of the monogeneans Macrogyrodactylus clarii and M. congolensis inhabiting the gills and skin respectively of the same host fish C. gariepinus.