Scanning electron microscopical studies on cercariae and metacercariae of Fasciola gigantica.

The surface topography of Fasciola gigantica cercariae and metacercariae was studied by scanning electron microscopy. The head of F. gigantica cercaria is covered with several small knobs and its tail is provided with two lateral folds, fused ventrally, near the distal end of the tail. The oral sucker is smaller than the ventral one and possesses a characteristic surface structure. The outermost layer (layer I) of the outer cyst wall of the metacercaria is roughened with irregular furrows. The inner surface of the outer cyst wall (layer II) is more homogeneous and nearly smooth. The outermost layer of the inner cyst wall (layer III) is smooth and lacks any furrows or tubercles. The differences between F. gigantica and F. hepatica cercariae and metacercariae are discussed.