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

Two species of Didymorchis (Turbellaria, Temnocephalida) from Lago Nahuel H uapi, Argentina were studied using a scanning electron microscope and silve r 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 recog nised. The syncytial plate topography of the South American species of Didy morchis has the following distinguishing characteristics: the presence of v entro lateral posterior syncytia, the absence of outer intermediate syncyti a, the higher number of plates than present on Australian and New Zealand s pecies, including the replications, and the position of the nephridiopores. The results presented provide data relevant to the origin and relationship s of the Didymorchidae within the Temnocephalida, and also their relationsh ips with their hosts.