Stereoscan observations of the miracidium and early sporocyst of Schistosoma mansoni.

Whole miracidia of Schistosoma mansoni, miracidia vibrated in an ultrasonic cleaner, and the miracidium-sporocyst transition were studied in the stereoscan electron microscope. After vibrating, the cilia broke off near the bases and the epidermal cells, intercellular ridge and sensory structures were revealed. The apical papilla had a folded surface with penetrating sensory cilia. The number of epidermal cells varied between 17 and 22. The lateral papillae appeared as bulbous projections on either side between the first and second tiers of epidermal cells. There was a ciliated pit nerve ending close to each lateral papilla. A few ciliated pits were found between the cells in the first tier, and up to twelve ciliated pits with long cilia could be found between the second and third tiers. Miracidia placed in haemolymph from Planorbarius corneus cast off the apical ciliated part of the epithelial cells, and large scars appeared where the ciliated plates had been. Later, the syncytial intercellular ridge dispersed throughout the surface of the mother sporocyst, and small cytoplasmic knobs appeared on the surface. The apical papilla and the lateral papillae were still observed a few hours after shedding the ciliated plates, but the ciliated pits disappeared shortly after the ciliated plates were lost.