The mosaic of the epidermal syncytia in Didymorchis sp (Didymorchidae, Temnocephalida) from South America

Two species of Didymorchis (Turbellaria, Temnocephalida) from Lago Nahuel Huapi, Argentina were studied using a scanning electron microscope and silver nitrate staining to demonstrate the presence of syncytial plates and map the epidermal mosaic. The Didymorchis species studied have twenty syncytia, more than are present in the Australian and New Zealand species. Otherwise, the same six morphological groups found in the other species can be recognised. The syncytial plate topography of the South American species of Didymorchis has the following distinguishing characteristics: the presence of ventro lateral posterior syncytia, the absence of outer intermediate syncytia, the higher number of plates than present on Australian and New Zealand species, including the replications, and the position of the nephridiopores. The results presented provide data relevant to the origin and relationships of the Didymorchidae within the Temnocephalida, and also their relationships with their hosts.