An overview of surface specializations in the digenetic trematodes

The outer covering of digenetic trematodes undergoes a number of changes in the course of the life cycle in adaptation to parasitism and to the host-seeking requirements of the various stages. Using Schistosoma mansoni as a model, I review morphological, physiological, and cytochemical features of the coverings of miracidia, sporocysts, cercariae, and adults. Such features should be used with caution in evaluating phylogenetic relationships of any flatworms since the environment is itself a powerful determinant.