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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.