Ultrastructural aspects of intramolluscan developing cercariae of Echinostoma liei

The ultrastructure of the daughter redia of Echinostoma liei inside their host Biomphalaria alexandrina is described. The tegument consists of one layer, bearing numerous microvilli on its outer surface. Besides, the description of the ultrastructure of the developing cercariae within the daughter rediae is also included in the present study. The young cercariae are covered with a thin nucleated primitive temporary epithelium, which is lost when the true tegument is formed beneath it. The mechanism of spine formation was not apparent, but there is some indication that the spines are associated with a thickened part of the basal membrane of the tegument. Section through these cercariae showed that the tissues lying below the tegument are disposed in consecutive layers, suggestively representing developing muscle tissues.