The tegument of the microphallid digenean Maritrema feliui, examined by means of TEM, is described as a syncytial epithelium organised into two layers. The outer layer is an external anucleate, cytoplasmic region connected to a second region composed of nucleate perikarya (cytons) deeply embedded in the surrounding cortical parenchyma. The surface layer of the tegument is covered by a plasma membrane with many deep invaginations, which are apparently pinocytotic. This layer also bears numerous large, electron-dense spines of two types, which are intracellular and attached to the basal plasma membrane. Its cytoplasm is rich in free ribosomes, contains numerous mitochondria, disc-shaped granules frequently arranged in a rouleau, and several large, moderately electron-dense, membranous bodies. The subtegumentary perikarya and their nuclei, which are both flattened, are described in detail, as are their connections with the surface tegument. These perikarya appear to be the source of the disc-shaped granules and some of the other inclusions present in the surface layer. The main characteristics of the tegumental structure of M. feliui are commented upon in relation to the findings of previous publications and their suggested functions.
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