EN
The envelopes of oncospheres of a hymenolepidid tapeworm with an aquatic life cycle Fimbriaria czaplinskii, surrounding larvae inside the gravid part of the strobila, were examined under a transmission electron microscope. Details of the ultrastructure of the outer envelope and the inner envelope with its two derivatives: the embryophore and oncospheral membrane are described. The ultrastructural features of F. czaplinskii envelopes are compared and discussed with those described previously in the other hymenolepidids, and particularly with the related species Fimbriaria fasciolaris.