Schistosoma japonicum: ultrastructural changes in the tegument during cercaria-schistosomulum transformation

The tegumental changes of Schistosoma japonicum cercaria were initiated when introduced into NCTC 109 containing antibiotics for axenizing. In some regions the tegument was covered with a penta- or heptalaminate membrane, and the surface coat changed into an electron-dense, amorphous material. Large vacuoles limited by a multilaminate membrane were evident in the tegumental cytoplasm, and some appeared to join or open to the tegument. After 4 h incubation in NCTC 109 containing 50% fresh rabbit serum, the outer tegumental membrane of schistosomulum became heptalaminate. The amorphous material was still present on the surface of the tegument. Within 72 h the tegument was covered with a heptalaminate membrane over a greater part of the body, and the amorphous material was very reduced. Large vacuoles in the tegument disappeared and tegumental folds developed in some regions. No amorphous material existed on the surface of 10-day schistosomulum and the outer membrane of the tegument was heptalaminate in almost all regions of the body.