TREMATODE SPECIES DETECTION AND QUANTIFICATION BY ENVIRONMENTAL DNA-qPCR ASSAY IN LAKE CHANY, RUSSIA.

Environmental DNA (eDNA) surveys promise to be a sensitive and powerful tool for the detection of trematodes. This can contribute to the limited studies on trematode ecology, specifically in aquatic ecosystems. Here, we developed species-specific primer and probe sets for Moliniella anceps, Opisthioglyphe ranae, and Plagiorchis multiglandularis cercariae and applied a novel eDNA qPCR assay to detect larval trematodes quantitatively. We evaluated the effectiveness of the assays using filtered lake water samples collected from different sites of Lake Fadikha and Kargat River Estuary in Lake Chany, Russia, showing high species specificity and sensitivity in all 3 assays. Further, all 3 assays had high efficiencies ranging from 94.9 to 105.8%. Moliniella anceps, O. ranae, and P. multiglandularis were detected in the environmental water samples through real-time PCR. Thus, we anticipate that our approach will be beneficial for biomonitoring, measuring, and managing ecological systems.

A new species of the genus Paradistomum (Platyhelminthes: Trematoda) from Iwasaki's snail-eating snake Pareas iwasakii, with a note on morphological variations of Paradistomum megareceptaculum (Tamura, 1941).

Dicrocoeliid trematodes were detected from Iwasaki's snail-eating snake Pareas iwasakii in Iriomote Island, Okinawa Prefecture, Japan, and described as a new species Paradistomum dextra n. sp. in the present study. This new species can be distinguished from the type series of the other members of the genus based on size of eggs and morphological characteristics of body, oral and ventral suckers, and reproductive organs. However, the new species was hard to distinguish from Paradistomum megareceptaculum infecting snakes in Japan, including Iriomote Island where is the type locality of the new species, because it is closely similar to some part of the broad range of morphological variations in P. megareceptaculum. On the other hand, a partial sequence of 28S ribosomal DNA clearly distinguished these two species. Moreover, the new species' host snake Pareas iwasakii is reported to exclusively feed on land snails while host snakes of P. megareceptaculum feed on small vertebrates, indicating that the new species is also ecologically different from P. megareceptaculum. We also redescribed P. megareceptaculum based on adults sampled in this study and past studies to record the morphological variations of this species.

Addressing the taxonomic confusion of Mesocoelium Odhner, 1910 (Trematoda: Plagiorchioidea: Mesocoeliidae) in Japanese urodelan and anuran amphibians.

Trematodes of the genus Mesocoelium Odhner, 1910 (Digenea: Plagiorchioidea: Mesocoeliidae) are globally distributed and parasitize amphibians, reptiles, or occasionally fishes. This genus is one of the most confusing taxa in trematodes because of its poor morphological features. In this study, we examined species of Mesocoelium collected from Japanese amphibians and found that they can be morphologically assigned to two species of Mesocoelium. Mesocoelium brevicaecum Ochi in Goto and Ozaki, 1929 parasitizes various both urodelan and anuran amphibians and occurred widely in Japan, while M. japonicum Goto and Ozaki, 1930 parasitizes a few hynobiid species in a limited part of Japan. We proposed ceca length as a valid key characteristic for species identification in this genus. M. elongatum Goto and Ozaki, 1929, M. lanceatum Goto and Ozaki, 1929, M. minutum Park, 1939, M. ovatum Goto and Ozaki, 1930, and M. pearsei Goto and Ozaki, 1930 are junior synonyms of M. brevicaecum, while M. japonicum can be distinguishable from them by morphologically and molecularly. Our molecular study supported the validity of both species and showed intraspecific divergence associated with geographic distance. Molecular identification suggests that the land snail Euhadra quaesita can serve as the first intermediate host for M. japonicum in Japan. This study also indicates the extremely low specificity of this genus for vertebrate hosts. Finally, we conclude that at least three species of Mesocoelium (M. brevicaecum, M. japonicum, and Mesocoelium sp. 1) are distributed in Japan. Further studies in other regions are undoubtedly required for a better understanding of the taxonomy and ecology of the genus Mesocoelium.

Molecular phylogenetic position and the life cycle of Phyllodistomum cyprini Feng et Wang, 1995 in Japan, with a note of a larval Phyllodistomum sp. from unionid mussels in North America.

A gorgoderid species, Phyllodistomum cyprini Feng et Wang, 1995 obtained from ureters of common carp, Cyprinus carpio in Japan is described both morphologically and molecularly. Its larval stage is a macrocercous cercaria found in a unionid mussel, Nodularia nipponensis first described by Urabe et al. (2015). A molecular phylogenetic study revealed that P. cyprini is not closely related to rhopalocercous cercariae from unionid mussels both in Europe and North America. This result indicates that there are several distinct clades in Phyllodistomum species that use unionid mussels as a first intermediate host, and suggests that the cercarial morphology may be a more accurate indicator of the phylogeny of Phyllodistomum than molluscan host identity.

Characterization of the complete mitochondrial genome of Plagiorchis multiglandularis (Digenea, Plagiorchiidae): Comparison with the members of Xiphidiatan species and phylogenetic implications.

Plagiorchis multiglandularis Semenov, 1927 is a common fluke of birds and mammals, with significant impacts on animals and also human health. However, the systematics of Plagiorchiidae remain ambiguous. In the present study, the complete mitochondrial (mt) genome of P. multiglandularis cercariae was sequenced and compared with other digeneans in the order Xiphidiata. The complete circular mt genome of P. multiglandularis was 14,228 bp in length. The mitogenome contains 12 protein-coding genes and 22 transfer RNA genes. The 3' end of nad4L overlaps the 5' end of nad4 by 40 bp, while the atp8 gene is absent. Twenty-one transfer RNA genes transcribe products with conventional cloverleaf structures, while one transfer RNA gene has unpaired D-arms. Comparative analysis with related digenean trematodes revealed that A + T content of mt genome of P. multiglandularis was significantly higher among all the xiphidiatan trematodes. Phylogenetic analyses demonstrated that Plagiorchiidae formed a monophyletic branch, in which Plagiorchiidae are more closely related to Paragonimidae than Prosthogonimidae. Our data enhanced the Plagiorchis mt genome database and provides molecular resources for further studies of Plagiorchiidae taxonomy, population genetics and systematics.

Integrative approach for discovering of the new species within the genus Allocreadium Looss, 1900 (Trematoda: Allocreadiidae) and framing of biogeographical hypotheses for the genus.

In July 2012 new Allocreadium species was isolated from Carassius gibelio caught in the Arsenyevka River, Primorsky region, Russia. Analyses on the morphometrics and internal organs' topology revealed that these worms are morphologically closest with A. isoporum but both species are independent according to high genetic distances based on the 28S gene fragment (5.434±0.0073%). Unlike A. isoporum found earlier in Europe, the new species named A. pseudoisoporum sp. nov. has a shorter body length and the vitellarium not reaching the posterior end of the body at some distance and its anterior border is on the level of the ventral sucker. Allocreadium pseudoisoporum sp. nov. differs from seven species previously found in the Russian Far East with the following features: smaller size of the body, suckers' ratio, range values, and topology of internal structures. Newly localities in the Pavlovka River and the Artyomovka River were discovered for A. khankaiensis. Morphological variability of the worms from the Pavlovka River was observed in comparison with A. khankaiensis from the Komissarovka River. Using scanning electron microscope, we examined external surfaces of three species (A. pseudoisoporum sp. nov., A. khankaiensis, A. hemibarbi) and observed structures reminiscent sensory receptors. This study was aimed to describe species diversity of allocreadiids inhabiting the south of Primorsky region, and to clarify phylogenetic relationships between the species from the genus Allocreadium Looss, 1900 using molecular genetic methods. The phylogenetic Bayesian tree based on the 28S gene showed a clear separation of ten Allocreadium species and confirmed the validity of A. pseudoisoporum sp. nov. Allocreadium pseudoisoporum sp. nov. is most similar to A. gotoi (genetic distances - 3.578±0.0051% in 28S, and 18.777±0.0149% in cox1), and represented the earliest divergent lineage in Allocreadium clade on the phylogenetic tree based on the 28S gene, thereby indicating its proximity to the ancestral node. Also, dichotomous keys for 25 Palearctic species of Allocreadium were prepared based on the morphology of the adult worms.

The complete mitogenome of Echinoparyphium aconiatum (Digenea: Echinostomatidae) and a comparison with other digenean species.

Echinoparyphium aconiatum (Digenea: Echinostomatidae) is an intestinal parasite of anatid and snail-eating birds. In Eurasia, it is also common in lymnaeid snails, which may serve as the first and second intermediate hosts. The systematics of its genus, Echinoparyphium, have long been inadequate, with poor descriptions and extensive synonymy. To provide a basis for developing new genetic markers for studies of the identification and systematics of echinostomatids, the complete Ep. aconiatum mitogenome is described and compared with other digeneans. The circular mt molecule of this species is 14,865 bp in length, with an average A + T content of 64.33%. It contains 12 protein-coding genes and 22 transfer RNA genes. The 3' end of nad4L overlaps the 5' end of nad4 by 40 bp, while the atp8 gene is absent. Twenty-one transfer RNA genes transcribe products with conventional cloverleaf structures, while one transfer RNA gene has unpaired D-arms. Comparative analyses indicate that Echinoparyphium aconiatum is closely related to Echinochasmus japonicus and Echinostoma miyagawai. The phylogenetic results, using our mitochondrial data indicated Ep. aconiatum as a sister taxon of Hypoderaeum conoideum in a monophyletic clade. Our data and analyses serve as the first representative sequenced mt genome from genus Echinoparpyhium, providing additional markers to clarify the taxonomic position of Ep. aconiatum.

Two new kathlaniid species (Nematoda: Cosmocercoidea) parasitic in salamanders of the genus Andrias (Amphibia: Caudata: Cryptobranchidae).

The new nematode species, Falcaustra hanzaki n. sp. and Urodelnema takanoensis n. sp. (Cosmocercoidea: Kathlaniidae), were found from the intestine of giant salamanders in Kyoto Prefecture, Japan. The first species is featured by the number and arrangement of caudal papillae (3 pairs of precloacal papillae, 8 pairs of postcloacal papillae and a single ventral precloacal papilla), the presence of a single pseudosucker, spicules equal in size (520-638 µm long), and V-shaped gubernaculum in males; vulva situated about 3/5 of a body in females. The second species is characterized by the number and arrangement of caudal papillae (5 pairs of precloacal papillae, 6 pairs of postcloacal papillae and a single ventral precloacal papilla), spicules equal in size (403-593 µm long), V-shaped gubernaculum in males; vulva situated about 3/5 of a body in females. The molecular phylogenetic analysis was performed using the partial 18S and 28S ribosomal DNA and the internal transcribed spacers 1 region in the nuclear DNA. This phylogenetic study raised a question about the validity of Family Kathlaniidae and related families of Cosmocercoidea.

Invasion of fish parasite Prosorhynchoides ozakii (Trematoda: Bucephalidae) into Lake Kasumigaura and surrounding rivers of eastern Japan.

In 2019 to 2021, the golden mussel Limnoperna fortunei and several freshwater fishes were sampled from 22 sites of the Tone River system including Lake Kasumigaura, Honshu, Japan, to examine the invasion of bucephalid trematodes. The parasite species identification was performed by morphological observation and DNA barcoding based on the sequences of nuclear 28S rDNA and mitochondrial cytochrome c oxidase subunit 1 (cox1). A total of 1719 mussels were collected from 10 sites, and trematode-infected mussels were detected from 8 sites with prevalences between 0.3 and 42.9%. The sporocysts and cercariae were identified as Prosorhynchoides ozakii, a newly introduced species in the river system. A total of 700 fish individuals belonging to 24 species were collected from 15 sites. Two species of catfishes (Silurus asotus and Ictalurus punctatus) harbored mature or immature adults of Pr. ozakii in the intestine with prevalences between 8.3 and 20% including both host species. The metacercariae of Pr. ozakii were found from the fins and epidermis of 13 fish species from 10 sites (prevalence 4.8-100%). Fishes were heavily infected with metacercariae in fins, which were surrounded by the infiltration of hemocytes and rodlet cells. A population genetic analysis of Pr. ozakii did not show an obvious bottleneck, suggesting the possibility that the parasite was intentionally and repeatedly introduced into the river system.

Phylogeography of Rhabdias spp. (Nematoda: Rhabdiasidae) collected from Bufo species in Honshu, Shikoku, and Kyushu, Japan including possible cryptic species.

The genus Rhabdias Stiles & Hassall, 1905 comprises lung parasites of amphibians and reptiles worldwide. In Japan, 9 species have been recorded, including Rhabdias incerta Wilkie, 1930 which has been reported only in Bufo species. In this study, to assess the diversity of R. incerta, we performed molecular analyses of Rhabdias species sampled from three species/subspecies of Japanese toads namely Bufo japonicus, B. japonicus formosus, and B. torrenticola, collected in various regions of Honshu, Shikoku, and Kyushu, Japan. DNA sequence divergence was compared using mtDNA (COI) and nuclear DNA (28S) to identify possible cryptic species. Morphological analysis was performed through light microscopy and scanning electron microscopy (SEM). The results revealed that Bufo spp. serve as hosts for at least three Rhabdias species. Morphologically, most samples were identified as R. incerta but with a longer body and larger buccal cavity than originally described. Rhabdias incerta appears to be specific to the genus Bufo and is further subdivided into two or three phylogroups based on subspecies divisions and biogeography of their host. Some Rhabdias specimens collected in this study resemble R. tokyoensis Wilkie, 1930, parasitic in hosts from the order Caudata, which suggests host switching. Both molecular and morphological analyses suggested the presence of undescribed and cryptic Rhabdias species within toads collected in Japan. This study was the first to molecularly characterize Rhabdias species in Japan, including novel sequences of R. incerta and two undescribed species.

First report of post-cyclic transmission in trematodes: Derogenes lacustris (Digenea: Hemiuroidea) in Patagonian freshwater fishes.

The transmission of adult parasites from prey to predatory hosts has been demonstrated for some acanthocephalan and one cestode species. Derogenes lacustris (Digenea: Hemiuroidea: Derogenidae) is a generalist parasite that infects, as an adult, the stomach of native and introduced freshwater fishes in Andean Patagonia. In the present work, the post-cyclic transmission of D. lacustris from native Galaxias maculatus (Galaxiidae) to introduced Oncorhynchus mykiss (Salmonidae) was proved experimentally. The observed transmission rate for this experimental infection was 19%. The body length of D. lacustris on day 14 post-infection was significantly greater than before transmission. The number of eggs also increased significantly after transmission, showing that D. lacustris can survive, grow and continue with egg production for at least 2 weeks in predatory salmonids. This study provides the first experimental evidence of post-cyclic transmission of trematodes and the results suggest that post-cyclic parasitism enables this species to broaden its range of hosts and distribution ranges in Argentinean Patagonia.

Paraharmotrema karinganiense n. gen., n. sp. (Digenea: Liolopidae) infecting the intestine of serrated hinged terrapin (Pelusios sinuatus), east African black mud turtle (Pelusios subniger), and South African helmeted turtle (Pelomedusa galeata) and a phylogenetic hypothesis for liolopid genera.

We herein describe Paraharmotrema karinganiense n. gen., n. sp. Dutton & Bullard (Liolopidae Dollfus, 1934) from specimens infecting the intestine of the serrated hinged terrapin (Pelusios sinuatus), east African black mud turtle (Pelusios subniger) (both Nwanedzi River, Mozambique), and South African helmeted terrapin (Pelomedusa galeata) (North-western Zululand, KwaZulu-Natal Province, South Africa). The new genus can be easily differentiated from the other accepted liolopid genera (Liolope Cohn, 1902; Helicotrema Odhner, 1912; Harmotrema Nicoll, 1914; Dracovermis Brooks & Overstreet, 1978) by the combination of having a linguliform body approximately 6-9 × longer than wide, tegumental spines/scales, a minute ventral sucker located in the anterior 1/7-1/8 of the body, deeply lobed testes that are transverse and abut the caeca (spanning the intercaecal space), a uterus that is lateral to the anterior testis (not ventral to the anterior testis), a lobed ovary that is dextral and nearest the posterior testis, and a vitellarium that does not extend anteriad to the level of the ventral sucker and that does not fill the intercaecal space. Nucleotide sequences of large subunit ribosomal DNA (28S) and internal transcribed space region (ITS2) from all analyzed specimens of the new species were identical, respectively; the 28S sequences differed from that of Liolope copulans Cohn, 1902 and from that of Harmotrema laticaudae Yamaguti, 1933 by 103 (8%) and 105 (8%) nucleotides, respectively. The 28S phylogenetic analysis recovered the new genus sister to a clade comprising L. copulans and H. laticaudae. A key to liolopid genera is provided herein. The present study comprises the first nucleotide-based phylogenetic placement of Harmotrema and first record of a liolopid from South Africa or Mozambique. It is the first proposal of a new liolopid genus in 43 yrs, and it documents a second liolopid genus from P. subniger while tripling the number of liolopid turtle hosts reported from the continent of Africa.

A record of juvenile Paragonimus skrjabini miyazakii from the urinary bladder of the Japanese toad, Bufo japonicus formosus.

We found juveniles of Paragonimus in the urinary bladder of a Japanese toad (Bufo japonicus formosus) captured in Kyoto. These were molecularly identified as Paragonimus skrjabini miyazakii Kamo, Nishida, Hatsushika et Tomimura 1961. This is the first report of P. s. miyazakii found in anuran hosts in Japan, indicating that anurans can be paratenic hosts of P. s. miyazakii, as is also the case for Paragonimus skrjabini skrjabini in China. This finding suggests that definitive hosts of P. s. miyazakii can be infected by eating not only crabs or mammal paratenic hosts, but also anurans.

A new species of hemiuroidean trematode from Hatcheria macraei (Siluriformes, Trichomycteridae) and Heleobia hatcheri (Gastropoda, Cochliopidae) in a Patagonian River.

A new hemiuroidean species, Genarchella pichileufuensis n. sp. (Derogenidae: Halipeginae), was found in the stomach of the siluriform freshwater fish, Hatcheria macraei (Girard, 1855), in the Pichileufu River, Patagonia, Argentina. Its rediae with immature cystophorous cercariae were found in the snail Heleobia hatcheri (Pilsbry, 1911) in the same site. The present new species is morphologically featured by having a cyclocoel in the hindbody unlike the other species of the genus. The characteristics of this species allowed us to amend the diagnosis of the genus Genarchella as follows: cyclocoel present or absent; testes symmetrical to tandem; ootype pouch present. In the phylogenetic analysis, G. pichileufuensis forms a well-supported clade with Genarchella spp. recovered from Mexican freshwater fishes. This clade is included in the cluster of representatives of the subfamily Halipeginae. So far, three hemiuroidean species, Thometrema patagonica (Szidat, 1956), Derogenes lacustris Tsuchida, Flores, Viozzi, Rauque et Urabe, 2021 and G. pichileufuensis n. sp., have been reported from freshwater fishes in Argentinean Patagonia.

Systematics of Crepidostomum species from the Russian Far East and northern Japan, with description of a new species and validation of the genus Stephanophiala.

Current article touched upon the issue of the complicated taxonomic status of some species from the genus Crepidostomum collected from the freshwater fish in the rivers of Primorsky region, Sakhalin, and Hokkaido Islands. Primary morphological analyses showed affiliation of the worms to the species C. farionis (Müller, 1784) Lühe, 1909; C. metoecus Braun, 1900b; C. chaenogobii Yamaguti and Matsumura, 1942; C. nemachilus Krotov, 1959. We described the new species Crepidostomum achmerovi sp. nov. that is a sibling species of C. nemachilus. Molecular-genetic investigation have shown that C. nemachilus and C. achmerovi sp. nov. are closely related to C. metoecus in both 28S rDNA and cox1 mtDNA markers. Crepidostomum nemachilus forms a separate branch within the C. metoecus clade on the 28S BI tree with strong statistical support and separate clade in relation to C. metoecus clade on the cox1 BI tree. Values of p-distances between Crepidostomum species were at intergeneric level. Crepidostomum metoecus species complex including five species (C. metoecus, C. nemachilus, C. oschmarini, C. brinkmanni, and C. achmerovi sp. nov.) was reconsidered as independent genus Crepidostomum sensu stricto. Minimum Spanning Network showed that C. nemachilus, C. metoecus and C. achmerovi sp. nov. were separated by large number of mutational events and represent independent phyletic lines. An amended diagnosis is provided for the subfamily Crepidostomatinae, the genera Crepidostomum s. str. and Stephanophiala Nicoll, 1909, along with keys to species of both genera.

Hemiuroidean trematodes from freshwater Patagonian fishes: description of a new species, distribution and molecular phylogeny.

A new trematode species, Derogenes lacustris Tsuchida, Flores, Viozzi, Rauque et Urabe n. sp. (Derogenidae: Derogeninae), from freshwater fishes is described using morphological and molecular approaches in Argentinean Patagonia. D. lacustris is the most common hemiuroidean species in the Limay River basin and parasitizes almost all the native and introduced Patagonian freshwater fish. This new species could be considered as the unique freshwater species in the genus Derogenes Nicoll, 1910. Another hemiuroidean species, Thometrema patagonica Szidat (Archiev Hydrobiol 51: 542-577, 1956) Lunaschi et Drago 2000 (Derogenidae: Halipeginae), is found from Percichthys trucha (Perciformes) in the Neuquén River basin. Its diagnosis and molecular data are provided by the present study. In the molecular analysis of the Patagonian hemiuroideans, T. patagonica composes a group with halipeginean species in the phylogenetic tree of 28S rDNA sequences, while D. lacustris is not included in the same group. D. lacustris also shows low intraspecific variation in COI sequences regardless of the localities or host species.

Three species of Exorchis Kobayashi, 1921 (Digenea: Cryptogonimidae) in the East-Asian region: morphological and molecular data.

New data have been obtained for three representatives of Exorchis; Exorchis convictus sp. n., Exorchis oviformis and Exorchis sp., from fish in the East-Asian region. For the first time, based on combined sequences of the ITS2 rDNA region and the 28S rRNA gene, Exorchis is confirmed to belong Cryptogonimidae. Based on analysis of a mitochondrial marker (cox1), the 'Japanese' and 'Russian' haplogroups are identified for E. oviformis isolated from Silurus asotus. One specimen of E. oviformis obtained in Japan is identical to the 'Russian' haplotype. Haplotype patterns are also observed for metacercariae of Exorchis sp. from Tanakia lanceolata and Carassius sp. fish in Kyushu Island (Japan).

Ancient drainage networks mediated a large-scale genetic introgression in the East Asian freshwater snails.

Biogeography and genetic variation of freshwater organisms are influenced not only by current freshwater connections but also by past drainage networks. The Seto Inland Sea is a shallow enclosed sea in Japan, but geological evidence showed that a large freshwater drainage had intermittently appeared in this area between the late Pliocene and Pleistocene. Here, we demonstrated that this paleodrainage greatly affected the genetic variation of the East Asian freshwater snails, Semisulcospira spp. We found that the mtDNA haplotypes originated in the Lake Biwa endemic Semisulcospira species at the upstream side of the paleodrainage were frequently observed in the riverine Semisulcospira species at its downstream side. The genome-wide DNA and morphological analyses consistently showed that there was no clear evidence of nuclear introgression between the Lake Biwa endemics and riverine species. These results suggest that the large paleodrainage had facilitated mitochondrial introgression and had broadly spread the introgressed mtDNA haplotypes to its downstream region around the Seto Inland Sea. Our study highlights the role of paleodrainages in shaping the genetic variation of freshwater organisms.

Morphological and molecular studies of Eudiplozoon nipponicum (Goto, 1891) and Eudiplozoon kamegaii sp. n. (Monogenea; Diplozoidae).

Eudiplozoon nipponicum (Goto, 1891) Khotenovsky, 1985 (Monogenea: Diplozoidae), is known to parasitise Cyprinus carpio Linnaeus and species of Carassius. In this study, we conducted a taxonomic re-examination of E. nipponicum using genetic analysis and morphological comparisons from different host species from a single water system. rDNA nucleotide sequences of the internal transcription spacer 2 (ITS-2) region (645 bp) showed interspecific-level genetic differences among diplozoids from species of Carassius and C. carpio (p-distance: 3.1-4.0%) but no difference among those from different species of Carassius (0-0.4%) or between those from C. carpio collected in Asia and Europe (0-1.1%). Large variation was observed among 346 bp cytochrome c oxidase subunit I (COI) sequences (0.3-16.0 %); the topology of the phylogenetic tree showed no relationship to host genera or geographical regions of origin. Morphological observation showed that average clamp size of diplozoids from C. carpio was larger than those from Carassius spp. The number of folds on the hindbody was 10-25 for diplozoids from C. carpio and 12-19 for those from Carassius spp. Thus, our ITS-2 sequence and morphological comparison results indicate that diplozoids from C. carpio and species of Carassius belong to different species. The scientific name E. nipponicum should be applied to the species infected to the type host, Carassius sp. of Nakabo (2013) (Japanese name ginbuna). The diplozoid infecting C. carpio (Eurasian type) should be established as a new species: Eudiplozoon kamegaii sp. n. A neotype of E. nipponicum is designated in this report because the original E. nipponicum specimens are thought to have been lost.