Comparative studies on surface ultrastructure of newly excysted metacercariae of Japanese lung flukes.

The surface ultrastructure of excysted metacercariae of five species of Japanese lung flukes: Paragonimus westermani, P. pulmonalis, P. miyazakii, P. ohirai and P. iloktsuenensis, were studied. Some differences were observed in the distribution of the spines and papillae among the five species. Single-pointed spines were generally developed in the antero-ventral region, and their development varied among species. Three morphological types of papillae were observed: large-domed, small-domed and pit type. Large-domed papillae were regularly located on the lip of suckers without variation among the five species. The small-domed and pit type papillae were arranged bilaterally and symmetrically on the body surface, and the distribution varied among the species, especially around the suckers. These results suggest that metacercariae of Paragonimus species can be distinguished by surface ultrastructure, especially by the distribution of papillae.