RESUMO
Scanning electron microscopy is used for the first time to study the surface topography of Ithyoclinostomum dimorphum (Diesing, 1850), collected from Ardea cocoi Linnaeus, 1766 on the floodplain of the upper Paraná River Basin, Brazil. The body surface exhibits annular furrows, ridges and sensory papillae but no spines, and the tegument is reticulate. The oral sucker is terminal, bears radial furrows and is surrounded by a collar. The ventral sucker is located close to the oral sucker but lacks a collar. When extruded, the cirrus can be seen to bear papillae in its base, and the aperture of the ejaculatory duct is visible distally. The excretory pore is dorso-subterminal. Various incrustations and secretions are present on the body surface. These detailed observations make it possible for to us speculate on the functional significance of some of our findings in relation to the large size and contractile nature of these worms, and their ability to survive and mate in an apparently hostile environment.
