Stereoscan studies of cercariae, metacercariae, and adults of Cryptocotyle lingua (Creplin 1825) Fischoeder 1903 (Trematoda: Heterophyidae).

The cercaria of Cryptocotyle lingua has simple pointed spines all over the body. Four pointed modified spines occur dorsally in the mouth, and similar spines surround the openings of the penetration glands. The modified spines are shed shortly after penetration and encystment in the fish host. Less than a week after encystment, cytoplasmic folds develop all over the tegument. After about 4 weeks the cytoplasmic folds have disappeared and the spines are now flattened and serrated. The external surface of adults from herring gulls is very similar to that of mature metacercariae. It is provided with scalelike serrated spines which are especially well developed ventrally on the anterior end.