Fasciola gigantica: surface topography of the adult tegument

Adult Fasciola gigantica are leaf-shaped with tapered anterior and posterio r ends and measure about 35 mm in length and 15 mm in width across the mid section. Under the scanning electron microscope its surface appears rough d ue to the presence of numerous spines and surface foldings. Both oral and v entral suckers have thick rims covered with transverse folds and appear spi neless. On the anterior part of the ventral surface of the body, the spines are small and closely-spaced. Each spine has a serrated edge with 16 to 20 sharp points, and measures about 20 mum in width and 30 mum in height. In the mid-region the spines increase in size (up to 54 mum in width and 58 mu m in height) and number, especially towards the lateral aspect of the body. Towards the posterior end the spines progressively decrease in both size a nd number. The tegumental surface between the spines appears highly corruga ted with transverse folds alternating with grooves. At higher magnification s the surface of each fold is further increased with a meshwork of small ri dges separated by variable-sized pits or slits. There are three types of se nsory papillae on the surface. Types 1 and 2 are bulbous, measuring 4-6 mum in diameter at the base with nipple-like tips, and the type 2 also have sh ort cilia. Type 3 papillae are also bulbous and of similar size but with a smooth surface. These sensory papillae usually occur in clusters, each havi ng between 2 and 15 units depending on the region of the body. Clusters of papillae on the lateral aspect (usually types 1 and 2) and around the sucke rs (type 3) tend to be more numerous and larger in size. The dorsal side of the body exhibits similar surface features, but the spines and papillae ap pear less numerous and are smaller. Corrugation and invaginations of the su rface are also less extensive than on the ventral side of the body.