Discocotyle sagittata (Leuckart, 1842) (Monogenea: Discocotylidae) is redescribed, based on specimens collected from the type host, Salmo trutta Linnaeus, from the type locality, Freiburg, Germany, supplemented with specimens from S. trutta and rainbow trout, Oncorhynchus mykiss (Walbaum) reared in an Austrian aquarium. The diagnosis of the genus Discocotyle Diesing, 1850 is emended. Discocotyle cirayn. sp. is described, based on immature, preadult and adult specimens from the salmonid, Parahucho perryi (Brevoort) at Eniwa, Hokkaido, Japan. Adult specimens of the new species were about twice as large as those of D. sagittata from S. trutta. When the type specimens of D. cirayn. sp. were examined together with museum specimens from P. perryi at Tsurui, Hokkaido, the body and clamp sizes were positively correlated to the host size. Their measurements from a smaller P. perryi at Tsurui overlapped with those of D. sagittata, showing that these size differences were not suitable differentiating keys. Discocotyle cirayn. sp. can be separated from D. sagittata by the morphologies of the female genital system (relatively anteriorly positioned ovary, short joint vaginal duct and much more strongly winding uterus). The genetic distances of COI mtDNA sequence between D. cirayn. sp. and D. sagittata were 18.0-18.6%. These remarkable genetic divergences also supported the distinct taxonomic status of D. cirayn. sp.

Infections by ectoparasitic trichodinid ciliates cause epidermal damages to artificially reared juvenile barfin flounder Verasper moseri of mariculture fisheries in Hokkaido, northern Japan. In the present study, morphological observation and molecular phylogenetic analysis using the small subunit ribosomal RNA gene (SSU rDNA) were performed to identify the trichodinid ciliates. Morphological analysis of denticles and adoral ciliary spiral demonstrated that the trichodinid ciliate belongs to the genus Trichodina within ten genera of Trichodinidae. Denticles of the trichodinid ciliate were clearly distinguishable from those of other Trichodina species by small denticle span, and extensive elongation of the central conical part and anterior ray apophysis. All the isolated ciliate had the same 1,699 base pair SSU rDNA nucleotide sequences, which revealed that the trichodinid ciliates comprised a single species. The SSU rDNA of the trichodinid ciliate showed the highest homology with that of T. pectenis (98.5%) among 30 species of trichodinid ciliates, and the two species formed a single Glade in the phylogenetic tree. However, no identical sequence with the present trichodinid ciliate was found in the database. We propose Trichodina hokkaidoensis n. sp. for the ciliate infecting artificially reared juvenile barfin flounder, based on both morphological and molecular phylogenetic analyses.