Ultrastructure of the tail of Echinostoma revolutum cercaria.

The ultrastructure of the tail fins and muscles of Echinostoma revolutum cercaria is described. The longitudinal muscles consist of a primitive type of transversely striated muscle fibres with a well-developed sarcoplasmic reticulum in the Z-band. The fins are formed by a longitudinal tegument fold containing the same components as the remaining part of the tail tegument. The difference between the body and tail tegument is discussed.