Ultrastructural observations on the redia of Echinostoma revolutum (Froelich, 1802).

E. revolutum redia digestive and excretory system ultrastructure, as well as body wall tegument were studied in TEM. The body tegument protrudes in short microvilli and contains uni- and multiciliate sensory endings. The anterior part of the digestive system (pharynx, short oesophagus) is lined with body tegument, the caecum being covered with a flat epithelium with sporadic microvilli. Oesophageal gland cells are filled with minute electron-dense granules. The excretory capillaries joined to large flame cells are composed of spirally wrapped cells, in the cytoplasm of which there are clusters of microtubules. The special features of the digestive system of echinostome rediae, as well as their significance in the antagonistic relationship to the partenitae of other families of trematodes and their pathogenic effect on the intermediate host, are discussed.