Ultrastructural and cytochemical observations on the body wall of the redia of Sphaeridiotrema globulus (Rudolphi, 1819)

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Abstract
The ultrastructure of the body wall of the redia of Sphaeridiotrema globulus is described. The tegument, which possesses numerous microvilli, is shown to be a syncytial, cytoplasmic layer connected to underlying subtegumentary ‘cells’ by cytoplasmic processes. Between the subtegumentary ‘cells’ are located the normal parenchyma cells of the body wall, which are believed to be important in carbohydrate storage. Mitochondria, Golgi complexes, endoplasmic reticulum and beta glycogen granules are located in the tegument and subtegumentary ‘cells’. In addition, large whorled bodies and dense secretory granules appear to be formed within the subtegumentary ‘cells’ prior to their passage into the outer tegument. It is suggested that these whorled structures are contributing to the growth of the tegument. Small membrane-bound ‘vesicles’ are also seen in the tegument and some of these may be pinocytotic in nature. Following incubation, horseradish peroxidase tracer was localized within ‘vesicles’ in both the tegument, subtegumentary ‘cells’ and parenchyma cells, which indicates that the redial body wall may be important in the uptake of nutrients. Phosphatase enzymes are abundant within the tegument, particularly in association with the plasma membranes and microvilli. These enzymes, which appear to have their origin in the endoplasmic reticulum of subtegumentary cells, are believed to be associated with the uptake of nutrients through the redial tegument.