ULTRASTRUCTURAL STUDIES ON THE TEGUMENT OF THE METACERCARIAE OF MEIOGYMNOPHALLUS-MINUTUS AND MEIOGYMNOPHALLUS-FOSSARUM (DIGENEA, GYMNOPHALLIDAE) IN CERASTODERMA-EDULE (BIVALVIA) FROM PORTUGAL

Unencysted metacercariae of Meiogymnophallus minutus (Cobbold, 1859) a nd the sibling species Meiogymnophallus fossarum (Bartoli, 1965) infec t the edible cockle, Cerastoderma edule (L.), with free metacercariae occurring simultaneously in the same host specimens in Portugal. Obser vations on the tegument of both species show that changes in the morph ology of the body surface occurs in the intermediate host. Scanning an d transmission electron microscopy revealed an alveoli-like tegument w ith palmate, digitated spines protruding from each individual alveolus . Uniciliated papillate receptors, which may or not may be recessed, w ere abundant, surrounding the suckers as well as being distributed on the body surface. Transmission electron microscopy revealed a signific ant number of 3 types of densely packed secretory vesicles, thin cyste rnae, and mitochondria in the surface tegument of the body, oral cavit y, and esophagus. No distinguishing differences were observed in the s urface ultrastructure of M. minutus and M. fossarum metacercariae.