Ultrastructure of the Redia of Cryptocotyle lingua

Abstract

Electron micrographs of the redia of Cryptocotyle lingua show many highly flexible, ribbonlike folds extending from the epithelial cells of its saccate intestine into the lumen. Nutritive phagocytosis is suggested by the entrapment of food globules by curved intestinal folds which loop to coalesce with the apical surface of the gut cells. Droplets impounded by these processes may then sink into the cytoplasm of the intestinal cells as vesicles. The body surface of the redia is characterized by the presence of numerous, broad, cytoplasmic projections, the integumental folds or flaps. It is proposed that the integumental folds engulf nutrients by pinocytosis in a manner similar to that indicated above for intestinal folds. Cavitations of the apical integumentary membrane, sparsely present along the outer surface of the redial body, are suggestive of micropinocytosis. Mitochondria, membrane-bounded vesicles, and glycogen-like granules are found in the integument. Circular and longitudinal muscle cells contain only beta glycogen particles, whereas both alpha and beta varieties of glycogen are present in parenchymal cells. Recent electron microscope studies have revealed some of the ultrastructural adaptations that enable trematode rediae to exist in the tissues of their molluscan hosts. Microvilli projecting from the redial integument, presumably to facilitate exchange of materials between parasite and host, have been described in Acanthoparyphium spinulosum by Bils and Martin (1966), and in Parorchis acanthus by Rees (1966). This report on the fine structure of the intestine, integument and body wall of the Cryptocotyle lingua redia extends these observations and provides an additional basis for future biochemical studies of host-trema-