Systematics and life cycles of four avian schistosomatids from Southern Cone of South America.

Relative to the numerous studies focused on mammalian schistosomes, fewer include avian schistosomatids particularly in the southern hemisphere. This is changing and current research emerging from the Neotropics shows a remarkable diversity of endemic taxa. To contribute to this effort, nine ducks (Spatula cyanoptera, S.versicolor, Netta peposaca), 12 swans (Cygnus melancoryphus) and 1,400 Physa spp. snails from Chile and Argentina were collected for adults and larval schistosomatids, respectively. Isolated schistosomatids were preserved for morphological and molecular analyses (28S and COI genes). Four different schistosomatid taxa were retrieved from birds: Trichobilharzia sp. in N. peposaca and S. cyanoptera that formed a clade; S.cyanoptera and S. versicolor hosted Trichobilharzia querquedulae; Cygnus melancoryphus hosted the nasal schistosomatid, Nasusbilharzia melancorhypha; and one visceral, Schistosomatidae gen. sp., which formed a clade with furcocercariae from Argentina and Chile from previous work. Of the physid snails, only one from Argentina had schistosomatid furcocercariae that based on molecular analyses grouped with T. querquedulae. This study represents the first description of adult schistosomatids from Chile as well as the elucidation of the life cycles of N.melancorhypha and T. querquedulae in Chile and Neotropics, respectively. Without well-preserved adults, the putative new genus Schistosomatidae gen. sp. could not be described, but its life cycle involves Chilina spp. and C. melancoryphus. Scanning electron microscopy of T. querquedulae revealed additional, undescribed morphological traits, highlighting its diagnostic importance. Authors stress the need for additional surveys of avian schistosomatids from the Neotropics to better understand their evolutionary history.

A new species and emendation of the seldom reported Enterohaematotrema Mehra, 1940 (Digenea: Schistosomatoidea), including a revised phylogenetic hypothesis for turtle blood flukes.

Enterohaematotrema Mehra, 1940 is emended herein based upon a review of the literature and a description of a new species (Enterohaematotrema triettruongi n. sp.) infecting yellow-headed temple turtles, Heosemys annandalii (Boulenger) (Cryptodira: Geoemydidae), in the Mekong River, Vietnam. The new species differs from the published descriptions of its congeners Enterohaematotrema palaeorticum Mehra, 1940 and Enterohaematotrema hepaticum (Simha, 1958) Simha & Chattopadhyaya, 1980 by having two distinctive oesophageal glands, a short and eversible cirrus (vs protrusive with 3 distinct processes), a dorsal common genital pore that is sinistral (vs ventral and medial), a transverse (vs longitudinal) external seminal vesicle, an oviducal seminal receptacle that is sinistral (vs dextral), and a vitellarium distributing from the caecal bifurcation (anterior to the ventral sucker) to the caecal tips (vs vitellarium not extending anteriad beyond ventral sucker in E. palaeorticum or vitellarium wholly posterior to the terminal genitalia in E. hepaticum). A phylogenetic analysis of the D1-D3 domains of the nuclear large subunit ribosomal DNA (28S) recovered Enterohaematotrema and Platt Roberts & Bullard, 2016 as sister taxa that share a recent common ancestor with the clade comprising Ruavermis Dutton & Bullard, 2020 and Coeuritrema Mehra, 1933. These flukes collectively comprise a monophyletic group of southeast Asian turtle blood flukes. This analysis also indicated that the massive, longitudinal metraterm of species of Enterohaematotrema and Uterotrema Platt & Pichelin, 1994 represents homoplasy (convergent evolution). The present study comprises the first morphological study of original specimens of any species of Enterohematotrema in more than 50 years and is the first molecular phylogenetic placement of the genus among the various turtle blood fluke lineages.

Are glial cells of the Digenea (Platyhelminthes) muscle cells?

Muscle cells of a digenean fish blood fluke, Aporocotyle simplex, aggregate along the periphery of the cerebral ganglia. Solitary myocytons and sarcoplasmic processes with muscle fibres give rise to long, narrow lamellate projections, which are visible along the periphery and within ganglia. These ultrastructural observations suggest a switching of glial functions to muscle cells and represent additional evidence of the phylogenetic lability of glial cells in bilaterians.

Heads or tails? Differential translational regulation in cercarial heads and tails of schistosome worms.

Schistosomes are obligate helminths responsible for over 218 million cases of human schistosomiasis in 78 countries around the world. Infection occurs when free-swimming cercariae penetrate human skin and initiate developmental progression into parasitic obligate worms that consume red blood cells. Transcriptomic studies of infectious cercariae reveal abundant mRNAs associated with energy metabolism and host invasion. However, the cercaria is mostly transcriptionally quiescent, suggesting that most mRNAs are primed prior to cercarial escape from the snail host. The use of transcriptomics to understand protein expression presumes that transcription and translation are functionally coupled and the cercarial stage has categorically been treated as a single unit for -omic analysis. Per contra, the relationship between transcription and translation in infectious cercariae has not been described. To understand the correlation between transcription and translation in cercariae, we separately measured nascent translation levels in cercarial heads, cercarial tails and in the developing schistosomula, the next stage of its life cycle. The loss of the cercarial tail is essential for the transformation from a cercaria to a schistosomulum. We observed that translation was initially limited and the translation rate accelerated during the first 72-hours after tail loss. When we tested nascent translation in cercarial heads, cercarial tails, whole cercariae, and 4-hour schistosomula, we found that translation is significantly upregulated in the cercarial tail when compared to the cercarial head and that translation was undetectable in heads using immunofluorescent image quantification (p = .0005). These data represent a major shift in how we understand the cercarial stage. The cercarial head is mostly transcriptionally and translationally quiescent while being sufficient for progression into a schistosomulum. In addition, transcription and translation are not linked in Schistosoma mansoni cercaria. Thus, our current conceptual approach of treating the cercaria as a single functional unit for -omic studies may be insufficient to understand cercarial development.

Amphiorchis stacyi n. sp. (Digenea: Spirorchiidae) in the heart of a green turtle from Florida, USA and the literature review of Amphiorchis (Price, 1934).

The present paper reports the occurrence of the seventh species in the genus Amphiorchis (Digenea: Spirorchiidae) collected from the heart of a green turtle found in Florida, USA. A taxonomic key to the species of Amphiorchis and a literature review for the genus are presented.

Acipensericola glacialis n. sp. (Digenea: Aporocotylidae) from heart of lake sturgeon Acipenser fulvescens Rafinesque (Acipenseriformes: Acipenseridae) in the Great Lakes Basin, Lake Winnebago System, USA.

Acipensericola glacialis n. sp. infects the heart of lake sturgeon, Acipenser fulvescens (Rafinesque), in the Lake Winnebago System and differs from its only congener, Acipensericola petersoni Bullard, Snyder, Jensen & Overstreet, 2008, by having a dendritic intestine, deeply-lobed testes, a post-ovarian oötype, and a common genital pore that is medial to the dextral caecum. Acipensericola petersoni has a non-dendritic intestine, testes that are not deeply lobed, an oötype that is at level of the ovary (ventral to the ovary), and a common genital pore that is dorsal to the dextral caecum. Comparison of the large (28S) and small (18S) sub-unit ribosomal DNA and internal transcribed spacer 2 (ITS2) regions between specimens of A. glacialis n. sp. and A. petersoni revealed 13 (of 1,621 nt; 99.2% similarity in the 28S), 8 (of 1,841 nt; 99.9% similarity in the 18S), and 11 (of 442 nt; 97.5% similarity in the ITS2) nucleotide differences. Collectively, these results comprise an unexpectedly high degree of morphological and molecular similarity given the geographical (Mississippi River Basin vs Great Lakes Basin) and phylogenetic (Polyodontidae vs Acipenseridae) separation of these hosts but seemingly did not reject a previous hypothesis concerning lake sturgeon dispersal from the Mississippi Refugium following the Wisconsin glaciation ~18,000 years ago. The new species is the first nominal blood fluke described from a sturgeon.

Three new species of blood flukes (Digenea: Aporocotylidae) infecting pufferfishes (Teleostei: Tetraodontidae) from off Bali, Indonesia.

We describe three new species of blood flukes (Aporocotylidae) and propose their classification within the genus Psettarium Goto & Ozaki, 1929. All three species were collected from the circulatory systems of pufferfishes caught off Bali, central Indonesia. Psettarium pulchellum n. sp. was found in the gills of both the narrow-lined puffer (Arothron manilensis de Procé) and the spiny blaasop (Tylerius spinosissimus Regan), while P. ogawai n. sp. and P. jimbaranense n. sp. were found in the gills of the reticulated puffer (Arothron reticularis Bloch & Schneider). The morphological characteristics of these taxa necessitated emendation of the diagnosis for the genus Psettarium, to accommodate the presence of an oral sucker, multiple or entirely post-caecal testes and a degenerate posterior testis. Features such as proportion of body length occupied by the oesophagus, and posterior caeca being ≥7× the length of anterior caeca, are no longer regarded as useful genus-level characters. Additionally, Sasala nolani is reassigned to this genus as Psettarium nolani n. comb. In phylogenetic analyses of the 28S and ITS2 rDNA regions, all three new taxa form a well-supported clade, together with Psettarium sinense and Psettarium nolani n. comb., the two other species of tetraodontid-infecting aporocotylids for which comparative rDNA data were available. The short branch lengths within this clade, despite dramatic morphological differences between the five species, suggest that rapid morphological diversification has occurred among the tetraodontid-infecting aporocotylids. The genus Psettarium has long been considered problematic. Further commentary is given on the history of this genus and how the issues presented might be resolved.

Physa marmorata (Mollusca: Physidae) as a natural intermediate host of Trichobilharzia (Trematoda: Schistosomatidae), a potential causative agent of avian cercarial dermatitis in Brazil.

Species of Trichobilharzia are the main etiological agents of cercarial dermatitis in humans, which is considered a re-emerging disease. Despite the diversity and global distribution of species of this genus, studies of Trichobilharzia are scarce in South America. The goal of our investigations is better understand the diversity, distribution and life cycle of avian schistosomes and their likely role in causing dermatitis in Brazil. As part of this effort, cercariae found in naturally infected Physa marmorata were identified by morphological and molecular (mitochondrial cox1, nuclear ITS1 and 28S gene regions) methods as Trichobilharzia sp. These cercariae are similar morphologically to T. jequitibaensis described previously from Brazil and similar genetically to the North American physid transmitted species T. querquedulae and T. physellae. This is the first report of a potential agent of cercarial dermatitis from naturally infected snails from Brazil and first molecular characterization of a South American species of Trichobilharzia. A discussion follows concerning the potential role of this species has in outbreaks of dermatitis in Brazil.

Gigantobilharzia melanoidis n.sp. (Trematoda: Schistosomatidae) from Melanoides tuberculata (Gastropoda: Thiaridae) in the United Arab Emirates.

Delicate filamentous schistosomatids detected in the intestinal veins of experimentally infected chickens are here described as a new parasite species, Gigantobilharzia melanoidis, and details of its life cycle are given. It is the first complete description of a schistosome species that uses Melanoides tuberculata as an intermediate host. Apharyngeate ocellate brevifurcate cercariae found in 65 out of 950 M. tuberculata collected in a pond in Al Aweer, United Arab Emirates were used as infection material. The new species can be distinguished from the other species of the genus by the following combination of characters: caecal reunion in males situated anterior to seminal vesicle, a very short gynecophoric canal (gynecophoric canal length/body length ratio lower than 0.05) supported by 12-14 thickened bands. Cercariae of G. melanoidis can be distinguished from other Gigantobilharzia cercariae described in the literature based on the combination of these characters: flame cell formula 2[3 + 3 + (1)] = 14 and relatively longer tail stem in relation to body (tail stem length/body length ratio = 2). Under laboratory conditions at a temperature between 24 and 26 °C, M. tuberculata started to shed cercariae 7 weeks after exposure to miracidia. The prepatent period of G. melanoidis in experimentally infected chicken lasted between 43 and 49 days. The parasite inhabits the blood vessels mainly of the small intestine. Sections of adult worms and eggs were also found in histocuts of parenchymatous organs. Results of phylogenetic analysis corroborated that G. melanoidis is a distinct species; however, they also confirmed that the genus Gigantobilharzia is in need of revision and in future might be split into several genera.

Sharing schistosomes: the elephant schistosome Bivitellobilharzia nairi also infects the greater one-horned rhinoceros (Rhinoceros unicornis) in Chitwan National Park, Nepal.

Because the digenetic trematode fauna of Nepal is poorly known, we began to search for schistosomes in and around Chitwan National Park (CNP) of southern Nepal. Both domestic and wild Indian elephants (Elephus maximus) are present, and we found one of two dung samples from wild elephants and 1 of 22 (4.5%) dung samples from domestic elephants to be positive for schistosome eggs. The morphology of the eggs and both cox1 and 28S sequences derived from the eggs/miracidia were consistent with Bivitellobilharzia nairi, reported here for the first time from Nepal. Also, 7 of 14 faecal samples from the Asian or greater one-horned rhinoceros (Rhinoceros unicornis) contained viable eggs indistinguishable from those of B. nairi. This identification was confirmed by comparison with both cox1 and 28S sequences from B. nairi eggs/miracidia derived from Nepalese and Sri Lankan elephants. This represents the first sequence-verified identification of a schistosome from any species of rhinoceros, and the first verified occurrence of a representative of Bivitellobilharzia (a genus of 'elephant schistosomes') in mammals other than elephants. Our work suggests that elephants and rhinos share B. nairi in CNP, even though these two members of the 'charismatic megafauna' belong to unrelated mammalian families. Their shared life style of extensive contact with freshwater habitats likely plays a role, although the snail intermediate host and mode of definitive host infection for B. nairi have yet to be documented. This report also supports Bivitellobilharzia as a monophyletic group and its status as a distinct genus within Schistosomatidae.

On the morphology and taxonomy of Griphobilharzia amoena Platt and Blair, 1991 (Schistosomatoidea), a dioecious digenetic trematode parasite of the freshwater crocodile, Crocodylus johnstoni, in Australia.

Griphobilharzia amoena Platt and Blair, 1991 was originally described as a dioecious trematode, parasitic in the circulatory system of the Australian freshwater crocodile, Crocodylus johnstoni, with the female completely enclosed in a gynecophoric chamber of the male and the 2 worms oriented anti-parallel to each other. A recent publication questions the original description, arguing that G. amoena is monoecious and, as a consequence, the species was transferred to Vasotrema Stunkard, 1928 (Spirorchiidae) as Vasotrema amoena n. comb. We provide photomicrographic evidence that the original description of G. amoena is correct and that Griphobilharzia Platt and Blair, 1991, is a valid monotypic genus containing G. amoena. An accurate understanding of the anatomy of G. amoena is not trivial and has implications for revealing the complex origins and evolution of the dioecious condition within the Schistosomatoidea.

Discovery-based studies of schistosome diversity stimulate new hypotheses about parasite biology.

This review provides an update of ongoing efforts to expand our understanding of the diversity inherent within the Schistosomatidae, the parasites responsible for causing schistosomiasis and cercarial dermatitis. By revealing more of the species present, particularly among understudied avian schistosomes, we gain increased understanding of patterns of schistosome diversification, and their abilities to colonize new hosts and habitats. Schistosomes reveal a surprising ability to switch into new snail and vertebrate host species, into new intrahost habitats, and may adopt novel body forms in the process. Often these changes are not associated with deep splits or long branches in their phylogeny, suggesting some are of relatively recent origin. Several hypotheses prompted by the new observations are discussed, helping to focus thinking on processes influencing not only schistosome diversification but also their pathogenicity and abundance.

Morphology and surface topography of the schistosome Bivitellobilharzia nairi from the Asian elephant (Elephas maximus maximus) in Sri Lanka.

Bivitellobilharzia nairi was first recorded from an Indian elephant (Elephas maximus) in Berlin. Infections with this parasite have become increasingly important in E. maximus maximus populations in Sri Lanka. The present work is the first morphological description of this schistosome from Sri Lanka. A number of adult worms were recovered from a dead Asian elephant near the elephant orphanage, Pinnawala, in Sri Lanka. The observed clinical features of the infected elephant included emaciation, subventral oedema and anaemia. Post-mortem results indicated that the liver was enlarged and adult schistosomes were found in the blood vessels of the liver parenchyma. The total number of worms recovered from a portion of the liver was 129,870, which is an average of 22 worms per 100 g of liver. The present study uses both light microscopic and scanning electron microscope (SEM) techniques for the morphological and topographical characterization of this parasite and to permit comparison with other species of schistosomes. Morphologically, these worms correspond very well to the description of B. nairi by Dutt & Srivastava (1955). Moreover, it is clear that B. nairi is a distinctive species easily differentiated from other schistosomes. The SEM study of the tegument of male worms shows that the surface of B. nairi is smoother than in other schistosomes.

Anserobilharzia gen. n. (Digenea, Schistosomatidae) and redescription of A. brantae (Farr & Blankemeyer, 1956) comb. n. (syn. Trichobilharzia brantae), a parasite of geese (Anseriformes).

A new genus, Anserobilharzia, is proposed to accommodate Anserobilharzia brantae n. comb. (syn. Trichobilharzia bran- tae Farr & Blankemeyer, 1956), a species of avian schistosome thus far found exclusively in anserini geese (Anser, Branta, Chen) from Europe and North America, and Gyraulus snails. Recent collections and subsequent molecular analyses showed that A. brantae was distinct from Allobilharzia and Trichobilharzia and grouped basal to Trichobilharzia. Using nuclear 28S, ITS and mitochondrial cox1 as genetic yardsticks, samples of A. brantae from North America and Europe were each other's closest relative and distinct from Allobilharzia and Trichobilharzia. Anserobilharzia brantae was also distinct when compared morphologically with other species of closely related avian schistosomes. The following descrip- tion is based on males, females, eggs, and cercariae. The new genus is characterized by a) ovoid egg (72-145µm x 44- 89 µm) with spine, b) male with > 500 testes and caecal reunion anteriad to seminal vesicle, c) cercariae with 5+1 flame cells, and d) intermediate hosts are planorbid snails. The only confirmed species of snail host is Gyraulus parvus in North America. Based on presented data, we propose a new genus and new combination for A. brantae justified by morpholog- ical, host use, and molecular characteristics.

Orientobilharzia Dutt & Srivastava, 1955 (Trematoda: Schistosomatidae), a junior synonym of Schistosoma Weinland, 1858.

In the last few decades, phylogenetic studies of the family Schistosomatidae based on molecular markers have revealed that members of the genus Orientobilharzia Dutt & Srivastava, 1955 belong within Schistosoma Weinland, 1858. In this study, the original descriptions and redescriptions of Orientobilharzia species and related revisions are reviewed, and it is confirmed that the morphological characters correspond with the results of the molecular studies. The two genera differ only in the number of testes; however, this character varies to a large extent within particular genera of the subfamily Schistosomatinae and cannot be used to justify the separation of Orientobilharzia from Schistosoma. Also, we have verified claims suggesting the synonymy of certain species of Orientobilharzia; the four valid species of this genus are transferred to Schistosoma and two new synonymies are formally presented. The following nomenclatural changes are made: Schistosoma Weinland, 1858 [syn. Orientobilharzia Dutt & Srivastava, 1955 (syn. nov.)]; Schistosoma bomfordi Montgomery, 1906 (comb. restit.); S. turkestanicum Skrjabin, 1913 (comb. restit.) [syns Ori. turkestanica var. tuberculata (Bhalerao, 1932) (syn. nov.) and Ori. cheni Hsü & Yang, 1957 (syn. nov.)]; S. dattai (Dutt & Srivastava, 1952) n. comb.; and S. harinasutai (Kruatrachue, Bhaibulaya & Harinasuta, 1965) n. comb. The generic diagnosis of Schistosoma is amended and a revised key to the subfamily Schistosomatinae Stiles & Hassall, 1898 is presented.

The neuro-muscular system in fresh-water furcocercaria from Belarus. I Schistosomatidae.

The neuro-muscular system (NMS) in cercariae of the family Schistosomatidae from Belarus was studied with immunocytochemical methods and confocal scanning laser microscopy. The specimens of Bilharziella polonica were compared with Trichobilharzia szidati and Trichobilharzia franki. The patterns of F-actin in the musculature, 5-HT-immunoreactive (IR), FMRFamide-IR neuronal elements and α-tubulin-IR in sensory receptors and nerves were investigated. No indications of structural differences in the musculature, the 5-HT-IR, FMRF-IR neuronal elements and the general distribution of sensory receptors were noticed between cercariae of Trichobilharzia spp. The number of 5-HT-IR neurons in the cercarial bodies is 16. In cercaria B. polonica, the tail musculature is weaker than in Trichobilharzia spp. A detailed schematic picture of the NMS in the tail of Trichobilharzia spp. cercaria is given. The function of NMS elements in the tail is discussed.

Molecular identification of Austrobilharzia species parasitizing Cerithidea cingulata (Gastropoda: Potamididae) from Kuwait Bay.

Avian schistosomes belonging to the genus Austrobilharzia (Digenea: Schistosomatidae) are among the causative agents of cercarial dermatitis in humans. In this paper, ribosomal and mitochondrial DNA sequences were used to study schistosome cercariae from Kuwait Bay that have been identified morphologically as Austrobilharzia sp. Sequence comparison of the ribosomal DNA (rDNA) 28S and 18S regions of the collected schistosome cercariae with corresponding sequences of other schistosomes in GenBank revealed high sequence similarity. This confirmed the morphological identification of schistosome cercariae from Kuwait Bay as belonging to the genus Austrobilharzia. The finding was further supported by the phylogenetic tree that was constructed based on the combined data set 18S-28S-mitochondrial cytochrome oxidase I (mtCO1) sequences in which Austrobilharzia sp. clustered with A. terrigalensis and A. variglandis. Sequence comparison of the Austrobilharzia sp. from Kuwait Bay with A. variglandis and A. terrigalensis based on mtCO1 showed a variation of 10% and 11%, respectively. Since the sequence variation in the mtCO1 was within the interspecific range among trematodes, it seems that the Austrobilharzia species from Kuwait Bay is different from the two species reported in GenBank, A. terrigalensis and A. variglandis.

Morphological features of the nasal blood fluke Trichobilharzia regenti (Schistosomatidae, Digenea) from naturally infected hosts.

The first author detected the nasal bird schistosome Trichobilharzia regenti in Iceland in Anas platyrhynchos in Landmannalaugar in autumn of 2003. Since then, measurements and morphological studies have been performed on fresh worms (fragments) obtained in the area from naturally infected ducks, A. platyrhynchos and Aythya marila. In the present study, we compare our findings to the original description of T. regenti by Horák et al. (Parasite 5:349-357, 1998) that relies upon worms obtained by experimental infections of A. platyrhynchos f. domestica and Cairina moschata f. domestica ducklings. Fragments obtained from naturally infected birds are markedly larger than those obtained in the experimental infection. Also, indistinct sex-related size difference was confirmed; males were more abundant in the material than females. Previously unknown morphological features detected in the present study include, e.g. subterminal spines on the oral sucker directed to the oral opening, spine pattern on the apical part of acetabulum and long tegumental spines (up to 16 µm) in the gonad and tail regions of both sexes. In males, we evaluated for the first time the morphology of the cirrus sac enclosing ejaculatory duct, prostata and the entire prostatic region, the course of vas deferens and the position of genital papilla. In females, the posterior part of the reproductive system was studied for the first time. The presence of the Laurer's canal was confirmed and its course from the oviduct to the surface, where spermatozoa were noticed to leave the canal, was described.

Mating system drives negative associations between morphological features in Schistosomatidae.

BACKGROUND: Sexual morphological features are known to be associated with the mating systems of several animal groups. However, it has been suggested that morphological features other than sexual characteristics could also be constrained by the mating system as a consequence of negative associations. Schistosomatidae are parasitic organisms that vary in mating system and can thus be used to explore links between the mating system and negative associations with morphological features. RESULTS: A comparative analysis of Schistosomatidae morphological features revealed an association between the mating system (monogamous versus polygynandrous) and morphological characteristics of reproduction, nutrition, and locomotion. CONCLUSIONS: The mating system drives negative associations between somatic and sexual morphological features. In monogamous species, males display a lower investment in sexual tissues and a higher commitment of resources to tissues involved in female transport, protection, and feeding assistance. In contrast, males of polygynandrous species invest to a greater extent in sexual tissues at the cost of reduced commitment to female care.

Molecular diversity of Trichobilharzia franki in two intermediate hosts (Radix auricularia and Radix peregra): a complex of species.

Recently, the systematic use of the molecular approach as a complement to the other approaches (morphology, biology, life cycle) has brought help for the identification of species considered as different in the past to be regrouped and synonymised, and distinctions to be drawn between species similar at the morphological level. Among these species, we tried to clarify the situation of Trichobilharzia frankiMüller and Kimmig, 1994, species that today include more than 50 haplotypes notably coming from larval stages isolated from intermediate hosts belonging to gastropods of the Radix genus. Cercariae were isolated in France and Iceland from various molluscs, before being analyzed, with their hosts, by molecular analysis of various fields such as the D2 and ITS of the ribosomal DNA and the COX1 of mitochondrial DNA. We thus show the presence of two clades depending on the specificity of their intermediate host in which they were isolated (Radix auricularia or Radix peregra), thus allowing separation of the species T. franki that had been described in the past as a probable new species.