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Acta Parasitologica, Vol.45, No. 4, 2000, 307-321
Niewiadomska Katarzyna (1), Czubaj Andrzej (2) - Ultrastructure of the excretory system in the metacercaria of Diplostomum pseudospathaceum Niew., 1984 (Digenea).

(1) W.Stefanski Institute of Parasitology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa; e-mail:; (2) Laboratory of Electron Microscopy, Faculty of Biology, University of Warszawa, Miecznikowa 1, 02-096 Warszawa; Poland

The ultrastructure of the proto- and paranephridial excretory systems in the metacercaria of D. pseudospathaceum is described. Basically, the protonephridial system in the metacercaria, although being more complex, does not differ in ultrastructure from that in the cercaria. All protonephridial canals have nuclei and septate desmosomes between neighbouring cells as well as desmosomes closing the canals. Contrary to the protonephridial system, the paranephridial one has a syncytial structure with few cell nuclei in the wall. No septate desmosomes were visible in cross- and longitudinal sections of the paranephridial canals and terminal pockets. The heterocellular gap junctions (nexus) between tegumental cytons and paranephridial canal walls have not previously been observed and described in diplostomid metacercaria. The possible function of these heterocellular gap junctions is discussed.

KEY WORDS: Diplostomum pseudospathaceum, metacercaria, Digenea, excretory system
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