Scanning electron microscope observations of the surface features of the digenean Astiotrema impletum (Looss, 1899) Looss 1900.

The surface topography of Astiotrema impletum (Looss, 1899) Looss, 1900, from the white tilapia Oreochromis niloticus showed regional variations in the distribution of spines allover the body. The spines are abundant on the tegument of the head region, and the outer border of the ventral sucker. No spines were observed on the genital pore, on the inner rim of both the oral and ventral suckers, and on the tegumental surface of the posterior extremity of the body where the excretory pore is located. The sensory papillae are dome-shaped and arranged in a bilateral symmetrical pattern on both the oral and ventral suckers. They are also concentrated on the posterior extremity of the body. Some of these papillae possess a short knob-like process, while others have no process. Gland duct-like apertures were observed in four regions of the body: on the tegument covering the anterior extremity of the oral sucker, on the inner rim of the ventral sucker, in the region close to the genital aperture and in the region lying anterior to the excretory pore. The possible functions of the spines, sensory papillae, and gland duct-like apertures were discussed.