Euzetrema knoepffleri: evidence for a synchronous cycle of the gastrodermal activity and an ‘apocrine–like’ release of the residues of digestion

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Abstract
Summary: Euzetrema knoepffleri (Monogenea, Monopisthocotylea), an endoparasite of Euproctus montanus (Amphibia, Urodela), has a partially haematophagous diet, resembling that of the Polyopisthocotylea. In spite of this, the ultrastructural characteristics of the gastrodermis are typical of Monopisthocotylea. As in the Monogenea already described, digestion is intracellular with a lysosomal process, but two original features are evident. First, there is a cyclic activity of all the digestive cells during digestion with a synchronization of events, which enables two characteristic stages to be distinguished. Secondly, the elimination of the waste is similar to an ‘apocrine’ process, in which the apical portion of cytoplasm filled with residual bodies or the entire cell is released into the caecal lumen.