[Scanning electron microscopic observation on the encysted and excysted metacercariae of Paragonimus heterotremus].

The surface ultrastructure of metacercariae of Paragonimus heterotremus was studied by scanning electron microscope. Encysted metacercaria was egg-shaped with a button-like structure on its end. The oral sucker of the newly excysted metacercaria was larger than the ventral sucker. Single-pointed spines were covered densely on all of the tegumental surface. There were two and three rings sensory papillae on the oral and ventral suckers, respectively. Six papillae of the most inner ring were distributed on the ventral sucker inner-pore symmetrically. A few sensory papillae were dispersed on each side of the anterior part of the worms. These papillae of some excysted metacercariae were arranged irregularly in two rows with 5 to 6 papillae in each row (Figs. 1-8).