Integrative taxonomy identifies a new species of Phyllodistomum (Digenea: Gorgoderidae) from the twospot livebearer, Heterandria bimaculata (Teleostei: Poeciliidae), in Central Veracruz, Mexico

Integrative taxonomy of Anaporrhutum mundae sp. nov. (Trematoda: Gorgoderidae), a parasite of the Munda round ray Urotrygon munda (Urotrygonidae) in Costa Rica

A new species of trematode of anaporrhutine gorgoderid, from the gill chambers of the Munda round ray Urotrygon munda in Costa Rica is described, based on an integrative taxonomic approach that includes the use of light and scanning electron microscopy, ITS2 and 28S rDNA sequencing, and phylogenetic analysis. Anaporrhutum mundae sp. nov. can be distinguished from congeneric species by a combination of morphological traits and particularly by having the genital pore opening at the level of the intestinal bifurcation. The new species also can be distinguished from all other species of Anaporrhutum, except A. euzeti Curran, Blend & Overstreet, 2003, by having fewer testicular follicles per testis. Anaporrhutum mundae sp. nov. also differs from A. euzeti in its forebody shape and by having different morphology and location of the vitellaria. The study of the tegumental surface of A. mundae sp. nov., as revealed by scanning electron microscopy, allowed detection of new morphological characters for a member of Anaporrhutinae that may be of taxonomic value. These are: a stylet cavity dorsal to the oral sucker with a large penetration gland opening on each side of the cavity and small penetration gland openings located ventral to the stylet cavity, arranged in a circle around the mouth. This represents the first record of an Anaporrhutum species from Costa Rica. Further, A. mundae sp. nov. represents the first parasite described or reported in this host.

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.

Genetic characterization and phylogenetic relationships of Phyllodistomum parasites in Indian subcontinent: insights from freshwater fish and shrimp hosts

Phyllodistomum is the large digenean group of fish parasites, with 25 species described so far in the Indian subcontinent. Here, we redescribed two adult species of Phyllodistomum (P. srivastava Rai 1964 and P. parorchium Jaiswal 1957) collected from freshwater fish Heteropneustes fossilis Bloch, 1974 and Glossogobius giuris Ham, 1822, respectively, and an unknown Phyllodistomum metacercaria from shrimp (Macrobrachium dayanum Henderson, 1893). These parasites were genetically characterized using 28S and first and second internal transcribed spacers (ITS1 and ITS2) regions of the nuclear ribosomal DNA and CoxI region of the mitochondrial (mt) DNA to establish the link between metacercaria and adult. Morphologically, both the unknown metacercaria in shrimp and adult Phyllodistomum srivastava in fish, resembled in terms of crenulated margin of hind body, arrangement of diagonal testes, bipartite seminal vesicle, and compact paired vitelline masses. The two adult parasite species, P. srivastava from P. parorchium, were different in terms of shape and size of the body, ratio of suckers, the absence of crenulated margin of hind body, a single chambered seminal vesicle, and deeply lobed paired vitelline masses, in the former species. Comparison of the 28S, ITS, and mtCoxI sequence data suggested P. srivastava and Phyllodistomum metacercaria belong to the same species, and supported the distinction between P. srivastava and P. parorchium. Exploring the potential impact of Phyllodistomum infection on host behaviour and health would be prospective areas for future research.

Morphological and molecular data on Phyllodistomum (Digenea: Gorgoderidae) from Brazil, with the description of a new species parasitizing Hoplias malabaricus (Bloch, 1794) (Osteichthyes, Erythrinidae)

Phyllodistomum pepirense n. sp. is described from the urinary bladder of Hoplias malabaricus (Bloch, 1794), sampled in the Jacaré-Pepira River in São Paulo state, Brazil. The isolates of the new species were recovered as a monophyletic group in the phylogenetic analysis of the 28S rRNA gene, which showed the new species as the sister taxa of Phyllodistomum virmantasi Pinacho-Pinacho, Sereno-Uribe, Hernández-Orts, García-Varela & Pérez-Ponce de León, 2021, a species sampled from an eleotrid fish in Southeastern Mexico. The new species differs morphologically from P. virmantasi by having a larger body size, slightly lobed testes and ovary, a mostly intercaecal uterus, slightly diverticulated caeca, and vitelline masses irregularly shaped. The new species is also readily distinguished from other species of Phyllodistomum Braun, 1899 reported from freshwater fishes in Brazil - namely, P. rhamdiae Amato & Amato, 1993 and P. spatula Odhner, 1902. The new species is herein described based on morphological characteristics, molecular data from D1-D3 domains of the 28S rRNA gene, host association, and geographical distribution.

Chelatrematidae n. fam., a new family of digenetic trematodes from the South Western Ghats, India, erected on the basis of morphological and molecular studies

On the basis of the morphological characterization of Chelatrema neilgherriensis Manjula & Janardanan, 2006 recovered from the freshwater fish Barilius gatensis (Valenciennes, 1844) in the Wayanad region of the Western Ghats, the diagnostic features of the genus Chelatrema Gupta & Kumari, 1973 have been modified. Based on the phylogenetic analysis of C. neilgherriensis and comparative morphology studies relative to members of other families of Gorgoderoidea Looss, 1901, this genus is placed in a new family Chelatrematidae n. fam. The studies revealed the molecular and morphological closeness of Chelatrema with Paracreptatrematina limi Amin & Myer, 1982, and the latter is transferred to this new family. Hence the new family Chelatrematidae n. fam. comprises the genera Chelatrema and Paracreptatrematina.

What's in a name? Taxonomic and gender biases in the etymology of new species names

As our inventory of Earth's biodiversity progresses, the number of species given a Latin binomial name is also growing. While the coining of species names is bound by rules, the sources of inspiration used by taxonomists are an eclectic mix. We investigated naming trends for nearly 2900 new species of parasitic helminths described in the past two decades. Our analysis indicates that the likelihood of new species being given names that convey some information about them (name derived from morphology, host or locality of origin) or not (named after an eminent scientist, or for something else) depends on the higher taxonomic group to which the parasite or its host belongs. We also found a consistent gender bias among species named after eminent scientists, with male scientists being immortalized disproportionately more frequently than female scientists. Finally, we found that the tendency for taxonomists to name new species after a family member or close friend has increased over the past 20 years. We end by offering suggestions for future species naming, aimed at honouring the scientific community's diversity and avoiding etymological nepotism and cronyism, while still allowing for creativity in crafting new Latin species names.

Plesiochorus irwinorum n. sp. (Trematoda: Gorgoderidae) from the urinary bladder of the hawksbill turtle, Eretmochelys imbricata (Testudines: Cheloniidae), off the east coast of Australia

Plesiochorus Looss, 1901 is a genus of Gorgoderidae infecting the urinary bladders of marine turtles globally. Currently, just two morphologically similar species are recognised, Plesiochorus cymbiformis (Rudolphi, 1819) Looss, 1901 and Plesiochorus elongatus Pigulevsky, 1953, which have been distinguished by molecular data and subtle morphological differences. Here we describe a new species, Plesiochorus irwinorumn. sp., infecting hawksbill turtles (Eretmochelys imbricata (L.)), which is primarily distinguished from the other two species of Plesiochorus on the basis of ITS2, cox1 and 28S sequence data. Morphometric data for specimens examined during this study overlap between P. cymbiformis and P. irwinorumn. sp. for every measured feature, rendering them functionally cryptic. However, principal components analysis clearly distinguishes the two species. Additionally, we report new specimens of P. cymbiformis, and provide new sequence data for specimens from Australian loggerhead (Caretta caretta (L.)) and hawksbill turtles. There is little understanding of the host-specificity or geographical distribution of the three species of Plesiochorus, and it remains possible that some of the previously reported sequences have been attributed to the wrong species.

Morphological and molecular assessment of the diversity of trematode communities in freshwater gastropods and bivalves in Los Tuxtlas tropical rainforest

Trematode life cycles involve molluscs as first intermediate hosts. The identification of trematodes based on the morphology of cercariae released from molluscs is challenging because the identification relies on adult forms obtained from their definitive hosts. Several studies have recently genetically characterized these larval forms establishing a link with adults sampled from their vertebrate hosts, allowing their identification at species level. In Los Tuxtlas tropical rainforest, in south-eastern Mexico, 57 species of trematodes have been reported from wildlife vertebrates; however, studies evaluating the diversity of trematode cercariae in molluscs are lacking. Here, we studied 11 species of molluscs to assess the diversity of cercariae in two lakes of Los Tuxtlas, Veracruz, Mexico; six of the 11 species were infected. Twelve cercarial morphotypes were collected and characterized morphologically. Sequences of the 28S ribosomal RNA gene were generated to allocate each morphotype into a family using the most recent phylogenetic classification of the Digenea as a framework; molecular work revealed 16 genetic lineages; some cercariae were identified up to genus (Apharyngostrigea, Ascocotyle, Centrocestus, Echinochasmus, Lecithodendrium and Posthodiplostomum), and some to species levels (Gorgoderina rosamondae, Langeronia macrocirra, Oligogonotylus manteri and Phyllodistomum inecoli) based on their phylogenetic position within the tree, and the genetic distance with respect to other sequenced congeners. Therefore, the cercarial morphotypes in the present study represent at least 16 putative species. Our study contributes to a better understanding of the trematode diversity in an area of high vertebrate species diversity, and to the knowledge of trematode life cycles.

Integrative taxonomy reveals an even greater diversity within the speciose genus Phyllodistomum (Platyhelminthes:Trematoda:Gorgoderidae), parasitic in the urinary bladder of Middle American freshwater fishes, with descriptions of five new species

Phyllodistomum is one of the most species-rich genera of parasitic platyhelminths, with 120 species described worldwide; they infect the urinary bladder of marine and freshwater fishes. As the number of new species within the genus has increased, morphological conservatism, and the lack of reliable diagnostic traits make the separation of species a challenging task. The increase of genetic data for Phyllodistomum species has permitted the use of an integrative taxonomy approach as a framework for species discovery and delimitation. DNA sequences (28S rRNA and COI mtDNA) were obtained from individuals of Phyllodistomum sampled in 29 locations across Middle America, and used in combination with morphology, host association and geographic distribution to uncover five new congeneric species. Morphologically, the new species are relatively similar; there are no unique morphological traits to readily distinguish them. We first investigated species boundaries through phylogenetic analyses of the independent and concatenated datasets; analyses recognised five candidate species showing reciprocal monophyly and strong clade support, particularly for COI data. The interspecific 28S rRNA and COI sequence divergence among the new species from 0.4 to 18.4% and from 5.1 to 27% respectively. These results were further validated by a Bayesian species delimitation approach. The five new species are well supported by molecular data used in combination with other sources of information such as host association and geographical distribution and are described herein as Phyllodistomum romualdae sp. nov., P. virmantasi sp. nov., P. isabelae sp. nov., P. scotti sp. nov., and P. simonae sp. nov.

Phyllodistomum kupermani n. sp. from the European perch, Perca fluviatilis L. (Perciformes: Percidae), and redescription of Phyllodistomum macrocotyle (Lühe, 1909) with notes on the species diversity and host specificity in the European Phyllodistomum spp. (Trematoda: Gorgoderidae)

BACKGROUND

European species of the large genus Phyllodistomum Braun, 1899 had historically been erected based solely on morphological characters. Unfortunately, many of them are still poorly known and inadequately described. Molecular approaches are critical to delineate species which were impossible to differentiate based on morphology alone.

METHODS

New samples of adult Phyllodistomum spp. were collected from the urinary bladder and/or ureters of European freshwater fishes and fixed to conduct a light and scanning electron microscopy study, and to obtain sequences of nuclear (ITS2 spacer and 28S rRNA gene), to be analysed in the context of a molecular phylogeny.

RESULTS

Based on new findings, a new species of Phyllodistomum from the urinary bladder of the European perch, Perca fluviatilis, in Volga River basin, Russia, is described. Additionally, new data on the morphology and tegumental surface topography of P. macrocotyle (Lühe, 1909) Odhner, 1911 from ureters of the common rudd, Scardinius erythrophthalmus, is presented. The host range of P. folium, confirmed by DNA analysis, is extended to other cyprinid fish species.

CONCLUSIONS

The present study has again shown that species of the genus Phyllodistomum are in dire need of revision based on both molecular analysis and detailed morphological redescriptions of the forms attributed to the genus. Morphologically, P. kupermani n. sp. most closely resembles P. pseudofolium, a highly host-specific parasite of Gymnocephalus cernuus (L.), but molecular phylogenetic analyses based on ITS2 and 28S rDNA sequences showed that these species are distantly related. Phyllodistomum kupermani n. sp. was found to be phylogenetically most closely related to the type-species of Phyllodistomum, P. folium. Phylogenetic analyses revealed that Phyllodistomum kupermani n. sp. and P. folium formed a clade with other freshwater species for which cystocercous cercariae develop in bivalves of the family Sphaeriidae. The micromorphology and tegumental surface topography of P. macrocotyle revealed in the present study provide a valuable taxonomic criterion for congeneric species differentiation.

New morphological and molecular data for Xystretrum solidum (Gorgoderidae, Gorgoderinae) from Sphoeroides testudineus (Tetraodontiformes, Tetraodontidae) in Mexican waters

Adults of trematodes in the genus Xystretrum Linton, 1910 (Gorgoderidae, Gorgoderinae) are parasites found exclusively in the urinary bladders of tetraodontiform fishes. However, limited and unclear morphological data were used to describe the type species, X. solidum Linton, 1910. Here, we present the first detailed morphological information for a member of Xystretrum. Morphological characters were described using light and scanning electron microscopy (SEM) of Xystretrum specimens from Sphoeroides testudineus (Linnaeus) (Tetraodontiformes, Tetraodontidae), collected at six localities off the northern Yucatan Peninsula coast of the Gulf of Mexico. We also compared sequence fragments of the 28S (region D1–D3) ribosomal DNA and mitochondrial Cytochrome c oxidase subunit 1 (COI) gene with those available for other gorgoderine taxa. We assigned these Xystretrum specimens to X. solidum, despite the incompleteness of published descriptions. The data provide a foundation for future work to validate the identities of X. solidum, X. papillosum Linton, 1910 and X. pulchrum (Travassos, 1920) with new collections from the type localities and hosts. Comparisons of 28S and COI regions described here also provide an opportunity to evaluate the monophyletic status of Xystretrum.

Diversity of helminth parasites of eight siluriform fishes from the Aguapeí River, upper Paraná basin, São Paulo state, Brazil

Fishes of the order Siluriformes, known as catfishes, have a global distribution with more than 3,600 valid species of which 2,087 occur in the Neotropical region. Despite being highly diverse, abundant, and of economic importance as food and ornamental fishes, knowledge about the diversity and distribution of their helminth parasites is fragmentary and scarce. Eight species of catfishes (Pterodoras granulosus, Trachydoras paraguayensis, Pimelodella avanhandavae, Loricariichthys platymetopon, Pterygoplichthys ambrosettii, Rhinelepis aspera, Hemisorubim platyrhynchos, and Sorubim lima) from the Aguapeí River, Upper Paraná River basin, municipality of Castilho, São Paulo State, Brazil, were surveyed for helminth parasites. Collected fishes were weighed, measured, and examined for helminth parasites following standard methodology. Fifty helminth parasite taxa (23 monogeneans, 13 digeneans, 11 nematodes, and three cestodes) were found from a total of 405 fishes screened. The helminth taxon that showed the highest mean intensity of infection and mean abundance was the nematode Rondonia rondoni from P. granulosus, followed by the nematode Parasynodontisia petterae from R. aspera. The ecological analyses were carried out at the component community level and at the infracommunity level. Trachydoras paraguayensis had the richest helminth component community. Pterygoplichthys ambrosettii had the most diverse helminth component community and R. aspera had the lowest. Both hosts are loricariids and have similar diet. However, the high parasite diversity of P. ambrosettii is due to the number of dactylogyrids species found (10), which are directly transmitted, whereas only three dactylogyrid species were found in R. aspera. At infracommunity level, the nematode species R. rondoni and P. petterae dominated the parasite communities. This study presents 38 new host records, contributing considerably to increase the diffuse knowledge of helminth parasites of Neotropical siluriforms.

Phyllodistomum vaili(Plagiorchiida: Gorgoderidae) infecting Parupeneus rubescens (Perciformes: Mullidae): morphology and phylogeny

Knowledge of the Arabian Gulf fish's parasite fauna is very poor. Until recently, only scattered reports from different locations are known for ecto- and endoparasites. Therefore, the present study aimed to investigate the digenean species that infects one of the most economically fish species in the Arabian Gulf, the rosy goatfish Parupeneus rubescens . One plagiorchiid species has been described, belonging to the Gorgoderidae family, and has been named as Phyllodistomum vaili Ho, Bray, Cutmore, Ward & Cribb, 2014 based on its morphological and morphometric characteristics. In order to accurately classify and characterize this plagiorchiid species, molecular analysis was carried out using both nuclear 18S and 28S rRNA gene regions and revealed that the present plagiorchiid species was associated with other species belonging to the Gorgoderidae family and deeply embedded in the Phyllodistomum genus, closely related to the previously described P. vaili (gb| KF013187.1, KF013173.1). The present study therefore revealed that the species Phyllodistomum is the first account as endoparasites from the rosy goatfish inhabiting the Arabian Gulf.

Molecular evidence for resurrection of Plesiochorus elongatus (Digenea: Gorgoderidae): An urinary bladder parasite of sea turtles

Trematodes of the genus Plesiochorus were recovered from the urinary bladder of a stranded female adult loggerhead sea turtle, Caretta caretta, on a beach in Rio de Janeiro State, Brazil. Morphological analysis of the specimens revealed characteristics resembling the sub-species Plesiochorus cymbiformis elongatus rather than the recently synonymised Plesiochorus cymbiformis. Molecular phylogenetic analysis of the ITS2 region also showed that P. c. elongatus was distinct from P. cymbiformis and related taxa. Further analysis of the ITS2 revealed substantial differentiation between P. cymbiformis from the USA and Brazil and the newly sequenced P. c. elongatus from Brazil, while a previously unspecified Plesiochorus sp. from the USA closely related to the novel Brazilian P. c. elongatus was reconciled as a USA isolate of P. c. elongatus. Based on both the morphological and molecular data it is suggested that P. c. elongatus should be referred to as Plesiochorus elongatus and be considered as the second species in the genus.

Two new species of Gyrodactylus von Nordmann, 1832 from Profundulus oaxacae (Pisces: Profundulidae) from Oaxaca, Mexico, studied by morphology and molecular analyses

In the present study, two new species of Gyrodactylus are described from Profundulus oaxacae, a fish endemic to the Pacific slope of Oaxaca State, Mexico. Fishes were collected within their distribution range in 5 localities in the Atoyac-Verde River. Gyrodactylus montealbani n. sp. and G. zapoteco n. sp. were erected and characterized morphologically (sclerites of the attachment apparatus and the male copulatory organ) and molecularly (sequences of the Internal Transcribed Spacer region of rDNA). The haptoral sclerites of the new species are similar to those of Gyrodactylus iunuri and Gyrodactylus tepari, both recently described from the goodeid fish Goodea atripinnis, from the Mexican States of Jalisco and Querétaro, respectively; and to Gyrodactylus xtachuna described from the poeciliid Poeciliopsis gracilis in Veracruz State, Mexico - nonetheless, these species can all be discriminated based on their marginal hook morphology. Specimens of G. montealbani n. sp. and G. zapoteco n. sp. were sequenced, and were aligned with sequences of 25 other Gyrodactylus spp. Both Maximum likelihood and Bayesian inference analyses indicated that the two new species are members of independent, well-supported lineages - these are the first Gyrodactylus species described from Profundulus oaxacae.

Host specificity, molecular phylogeny and morphological differences of Phyllodistomum pseudofolium Nybelin, 1926 and Phyllodistomum angulatum Linstow, 1907 (Trematoda: Gorgoderidae) with notes on Eurasian ruffe as final host for Phyllodistomum spp

Background

Host-specificity patterns are not well-defined for trematodes of the genus Phyllodistomum Braun, 1899. The Eurasian ruffe, Gymnocephalus cernuus L., has been recorded as a definitive host for Phyllodistomum folium (Olfers, 1816), P. angulatum Linstow, 1907 and P. megalorchis Nybelin, 1926 and as the type-host for P. pseudofolium Nybelin (1926). A wide range of other host fishes have been recorded for these species as well. All present host records have been based on light microscopy and the life-cycles of P. pseudofolium, P. angulatum and P. megalorchis are unknown. The validity of P. pseudofolium and P. megalorchis require verification. In this study, rDNA sequences generated from adult Phyllodistomum spp., as well as from larval stages developing in Pisidium amnicum Müller, were analysed to establish the real number of Phyllodistomum species utilizing G. cernuus, and to associate larvae with the corresponding adult forms.

Results

Phylogenetic analyses of adult and larval stages of Phyllodistomum spp. based on ITS2 and partial 28S rDNA data allowed the confirmation of the validity of P. pseudofolium. A macrocercous cercaria, known as Phyllodistomum sp. from P. amnicum is genetically identical to adult P. pseudofolium. Phyllodistomum megalorchis obtained from its type-host, Lota lota L., showed no genetic differences from P. angulatum parasitizing Sander lucioperca L. In our analysis, P. pseudofolium, P. angulatum and P. macrocotyle formed a highly supported clade despite the fact that these species appear to be associated with distinct patterns of first intermediate host identity and cercarial morphology. Some morphological differences between gravid specimens of P. pseudofolium and P. angulatum were observed and their SEM tegumental surface topography is described.

Conclusions

The results lead us to the perception that macroevolutionary host switching in the genus Phyllodistomum is independent of host phylogeny. This study suggests strict host-specificity (oioxeny) for P. pseudofolium using one first intermediate host species (P. amnicum) and one definitive host species (G. cernuus). Phyllodistomum megalorchis is to be regarded as a synonym of P. angulatum. The close phylogenetic relatives, P. pseudofolium and P. angulatum, can be differentiated by morphological traits, the micromorphology and tegumental surface topography of these two species is intended to provide useful data for their identification and support the use of such features as a valuable taxonomic criterion. Molecular data showed that G. cernuus is a definitive host for two species: the oioxenous P. pseudofolium and the euryxenous P. folium.

Phyllodistomum spinopapillatum sp. nov. (Digenea: Gorgoderidae), from the Oaxaca killifish Profundulus balsanus (Osteichthyes: Profundulidae) in Mexico, with new host and locality records of P. inecoli: Morphology, ultrastructure and molecular evidence

Phyllodistomum spinopapillatum sp. nov. is described from the urinary bladder of the Oaxaca killifish, Profundulus balsanus Ahl (Profundulidae) in Rio Pueblo Viejo and Rio Santa Cruz, Oaxaca, southwestern Mexico. The new species is described based on evidence gathered from morphology, scanning electron microscopy (SEM), and partial sequences of the 28S rRNA gene. Diagnostic characters of the new species of Phyllodistomum Braun 1899 are the presence of spines on the entire body surface and having a ventral sucker almost half the size of oral sucker. The new species possess a large number of dome-like papillae on the body surface with scattered distribution along the hindbody, and these papillae are characteristically spinulated. Phyllodistomum spinopapillatum sp. nov. most closely resembles P. inecoli Razo-Mendivil, Perez-Ponce de Leon and Rubio- Godoy, 2013, a parasite of the twospot livebearer Pseudoxiphophorus bimaculatus (Heckel) from Veracruz, in the Atlantic slope of Mexico. In addition to the new species, specimens of P. inecoli were also found parasitising the urinary bladder of cyprinodontiforms such as the Mexican molly Poecilia sphenops Valencienes in a pond at Santa Maria Coyotepec, and in Profundulus sp. in Rio Templo, both in Oaxaca, and in the Porthole livebearer Poeciliopsis gracilis (Heckel) in Rio San Juan, as well as in Profundulus punctatus (Gunter) from Rio Nueva Francia, both in Chiapas. The distribution and host range of P. inecoli is extended to freshwaters of the Pacific slope of Mexico, and to other cyprynodontiforms.

The life cycle and molecular phylogeny of a gorgoderid trematode recorded from the mussel Nodularia douglasiae in the Yodo River, Japan

In 2009, a novel larval trematode of the family Gorgoderidae was found in the gonads of Nodularia douglasiae (Unionidae) from the lower reaches of the Yodo River, Osaka Prefecture, Japan. This is the first collection of trematodes in a unionid mussel in Japan. We investigated the morphology and life cycle of the trematode, and conducted a molecular phylogenetic analysis with other gorgoderid species, both those collected in the Yodo River water system and those reported in the literature. Immature adult worms were obtained from the ureters of the common carp Cyprinus carpio, the first known instance of a gorgoderid from these fish in Japan. Morphological characteristics and molecular data show that it belongs to the subfamily Gorgoderinae (genus Phyllodistomum sensu lato). Regarding the morphology, first intermediate host, and the infection site of adult worms, it resembles Phyllodistomum elongatum Nybelin, 1926 from Europe, but no comparable molecular data exist for Ph. elongatum. Three cytochrome c oxidase subunit I haplotypes were detected in the specimens analyzed, suggesting that the present species is indigenous to the Yodo River water system. The 28S ribosomal DNA data showed that this species is a member of the clade consisting of Ph. cf. symmetorchis, Ph. folium, Pseudophyllodistomum and Xystretrum. However, its phylogenetic position within the clade differs between the maximum likelihood and maximum parsimony trees, and the sister species of the present species remain unclear.