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This study aimed to investigate the occurrence of larval trematode infections in bithyniid snails across five provinces in southern Thailand. A total of 1,413 Bithynia siamensis snails were collected between October 2021 and October 2022 using handpicking and scooping methods. Among these, 844 were identified as B. s. siamensis and 569 as B. s. goniomphalos. The snail samples were examined for parasitic infections in the laboratory using shedding and crushing methods. Among the 27 sampling sites, snails from 6 sites were infected with various trematode species (infection rate: 4.95%, 70/1,413). Evaluation of the morphological and internal organ characteristics of the cercariae allowed for the categorization of the trematodes into five species of trematodes (belonging to four families). The identified species included Echinochasmus pelecani (family: Echinostomatidae), Echinostoma revolutum (family: Echinostomatidae), Haematoloechus similis (family: Haematoloechidae), Loxogenoides bicolor (family Lecithodendriidae), and Stictodora tridactyla (family: Heterophyidae), and the infection rates for these species were 3.26% (46/1,413), 0.35% (5/1,413), 0.42% (6/1,413), 0.78% (11/1,413), and 0.14% (2/1,413), respectively. The cercariae from the identified trematode species were studied for DNA analysis. The phylogenetic lineage reveals relationships among the species, confirming the morphological distinctions., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Trematodes and their snail hosts have developed intimate parasite-host associations, with snails supporting a diverse and often species-specific trematode fauna. In the faucet snail, Bithynia tentaculata (Caenogastropoda, Littorinimorpha), a unique trematode fauna has been recorded recently. However, knowledge of the exact species identity, phylogenetic relationships, and geographical distribution remains limited as many of the species belong to groups with unclear or controversial taxonomical assignment. To contribute to our knowledge of the trematodes, we investigated the trematode fauna of B. tentaculata by examining a total of 556 snails from lakes in County Galway, Ireland. Using an integrative taxonomic approach including DNA sequence data analyses (28S rRNA gene, ITS1-5.8S-ITS2, ITS2, cox 1, nad 1) and morphological tools (taxonomical drawings and measurements), we identified nine trematode species of seven families, with seven species occurring as cercariae ( Cyathocotyle prussica , Lecithodendrium linstowi , Lecithodendrium sp., Asymphylodora progenetica , Sphaerostoma bramae , Metorchis xanthosomus , and Notocotylus sp.) and three species occurring as metacercariae ( A. progenetica , Parasymphylodora parasquamosa , and Sphaeridiotrema sp.). Except for S. bramae , all are new species records for Ireland and provide the most western distribution of these trematodes in Europe. The trematode species recorded are known to use a wide range of definitive hosts and have a wide geographical distribution; among them are species members of genera that are zoonotic ( Metorchis ) and pathogenic to wildlife ( Cyathocotyle , Sphaeridiotrema , and Notocotylus ). There remains an ongoing need for precise identification of the trematode species to ensure that wider ecological contexts are correctly understood and biodiversity and disease threats can be accurately evaluated.

Lymnaeid snails are some of the most widespread snails and are the first intermediate host of trematode parasites that affect human and livestock health. A full understanding of the genetic relationship of hosts and parasites is of paramount importance for effective parasite management. The present study assessed the prevalence of trematode larvae in lymnaeid snails and examined the genetic diversity of these snails collected across Thailand. We collected 672 lymnaeid snails from 39 locations in 22 provinces of six regions in Thailand. Subsequently, cercarial infection in the snails was observed by using the shedding method. Lymnaeid snails released 5 types of trematode cercariae, namely, xiphidiocercariae, echinostome cercariae I, echinostome cercariae II, furcocercous cercariae, and strigea cercariae. The phylogenetic analysis based on ITS2 and 28S rDNA sequences revealed 5 cercaria types assigned to four trematode families, of which two belong to the group of human intestinal flukes. Combination of shell morphology and sequence analysis of the mitochondrial COI and 16S rDNA genes, the lymnaeid snails were classified into two species, Radix rubiginosa and Orientogalba viridis. Moreover, the combined dataset of mtDNA genes (COI + 16S rDNA) from R. rubiginosa and O. viridis revealed 32 and 15 different haplotypes, respectively, of which only a few haplotypes were infected with cercariae. The genetic diversity and genetic structure revealed that R. rubiginosa and O. viridis experienced a bottleneck phenomenon, and showed limited gene flow between populations. Population demographic history analyses revealed that R. rubiginosa and O. viridis experienced population reductions followed by recent population expansion. These findings may improve our understanding of parasite-lymnaeid evolutionary relationships, as well as the underlying molecular genetic basis, which is information that can be used for further effective control of the spread of trematode disease., Competing Interests: Declaration of competing interest The authors declare there are no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Pulsating broodsacs of Leucochloridium sp. (Trematoda: Leucochloridiidae) were found from amber snails (Succinea lauta) in Iwate, the northern part of Honshu, Japan. A pattern with red-brown vertical stripes was characteristic of the broodsac. Very similar broodsacs were already detected from Okinawa Islands, the southern archipelago of Japan, and tentatively identified as Leucochloridium cf. passeri. A phylogenetic analysis based on DNA sequences of mitochondrial cytochrome c oxidase subunit 1 (cox1) showed that Leucochloridium sp. is different at species level from L. cf. passeri and that both species are related to Leucochloridium vogtianum from Europe. In this study the definitive identification of larval Leucochloridium sp. was impossible, but the resulting phylogeny confirmed that at least 4 species of Leucochloridium are distributed in Japan, depending on locality and climate. The DNA barcode generated in this study will be useful in detecting the adult stage of Leucochloridium sp. from birds., (Copyright © 2021 Elsevier B.V. All rights reserved.)

We found metacercariae of a microphallid trematode Atriophallophorus minutus in freshwater snails Bithynia tentaculata. In this study, we provide a morphological description of whole-mount specimens and semi-thin sections of experimentally grown adults of this species. Our morphological examination supports the idea that the adults of Atriophallophorus spp. have a ventral sucker with a sinistral interruption of the outer edge. In the 28S rDNA gene-based phylogenetic analyses, our specimens of A. minutus were grouped into Atriophallophorus spp. clade, as a sister taxon to Atriophallophorus winterbourni + Atriophallophorus sp. Analysis of the pairwise genetic distances between coI mtDNA gene sequences revealed a low divergence between the two specimens of A. minutus (1.1%) and a greater divergence (up to 16.6%) between them and A. winterbourni. Since other Atriophallophorus spp. are known to have a strict specificity to the polyvalent intermediate host, we suggest that A. minutus reported from different snail species may represent a complex of cryptic species., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The metacercarial infections of door snails (Gastropoda: Clausiliidae) with unknown species of the genus Brachylaima (Trematoda: Brachylaimidae) have recently been reported in eastern Honshu and Kyushu, Japan. A large scale snail survey was carried out to clarify their taxonomic status. From the period of 2015 to 2020, a total of 1239 land snails (768 door snails and 471 others) were collected from 32 localities in Honshu, Shikoku, and Kyushu. The resulting trematode isolates were identified as Brachylaima sp. by mitochondrial DNA barcoding. The sporocysts were found only a few from Megalophaedusa sublunellata (Clausiliidae), Tauphaedusa subaculus (Clausiliidae), and Aegista trochula (Camaenidae), while the metacercariae were frequently detected from 14 species of Clausiliidae and 2 species of other families. Although Brachylaima sp. showed a broad range of intermediate hosts, door snails seem to be very important to drive the life cycle. The gravid adults of Brachylaima sp. was experimentally raised from metacercariae using immunosuppressed mice. Morphological, phylogenetical, and ecological considerations prompted us to propose Brachylaima phaedusae n. sp. for this unknown species. The definitive hosts of the new species are completely unknown. The wide geographic distribution and high genetic diversity of the new species suggest a possibility that the definitive host is ground-foraging birds, which prefer door snails., (Copyright © 2021. Published by Elsevier B.V.)

Amphistome species belonging to the genus Catadiscus are poorly studied intestinal trematodes found primarily in Neotropical anurans. Herein, developmental stages of an amphistome species found during herpetological and malacological surveys in a temporary marsh pond from Brazil were subjected to morphological (light and scanning electron microscopy) and molecular analyses. Adult parasites recovered from anurans were identified as Catadiscus marinholutzi. Amphistome cercariae found in the planorbid snails Drepanotrema depressissimum and Drepanotrema lucidum from the same waterbody were used for experimental and molecular studies. Immature parasites, morphologically compatible with members of Catadiscus, were experimentally obtained in laboratory-reared tadpoles. Sequencing of a partial region of 28S rDNA gene of both adult and cercariae revealed 100% similarity between these developmental stages, confirming their conspecificity. Phylogenetic analyses were attempted for the first time to reveal the position of a species of Catadiscus in the superfamily Paramphistomoidea. Catadiscus marinholutzi falls in a virtual polytomy together with other paramphistomoids, which leaves its phylogenetic relationships within the group unclear. Moreover, the high genetic divergence to Diplodiscus spp. (10.06–10.84%) cast doubts on the placement of Catadiscus within Diplodiscidae. Hence the species composition of the Diplodiscidae should be re-evaluated in further studies using a broader spectrum of related taxa.

We investigated the prevalence, morphological characters and molecular classifications of trematode cercariae in freshwater snails randomly collected from 59 sampling localities in Bangkok from May 2018 to March 2019. We used a crushing technique to observe the cercarial stage inside each snail body and amplified the internal transcribed spacer 2 regions of cercarial DNA using polymerase chain reaction methodology. The associated phylogenetic tree was reconstructed using Bayesian inference analyses. A total of 517 of 15 621 examined snails were infected with trematode cercariae, and the infected snails were classified into 11 species of seven families with a 3.31% overall prevalence of the infection. The Bithynia siamensis siamensis snail displayed the highest prevalence of infection (16.16%), whereas the Physella acuta snail exhibited the lowest prevalence (0.08%) of infection. Eight morphological types of cercariae were observed. The highest prevalence of infection was observed in mutabile cercaria (1.86%). Based on molecular investigations, the phylogram revealed eight cercaria types assigned to at least nine digenean trematode families, of which five belong to groups of human intestinal flukes. Although, with the exception of schistosome cercaria, trematode cercariae are not known to directly damage humans, understanding the general biology of trematode cercariae (including diversity, distribution, infection rates and host range) is important and necessary for the prevention and control of parasitic transmission that impacts aquatic cultivations, livestock farming and human health.

The morphology of sexual adults is the cornerstone of digenean systematics. In addition, life cycle data have always been significant. The integration of these approaches, supplemented with molecular data, has allowed us to detect a new species that many researchers may have previously seen, but not recognized. Sexual adults from common eiders that we found in northern European seas were extremely similar to other notocotylids, but the discovery of their intermediate host, a marine snail, revealed the true nature of this material. Here we describe sexual adults, rediae and cercariae of Catatropis onobae sp. nov. We discuss how 'Catatropis verrucosa' should be regarded, justify designation of the new species C. onobae for our material and explain why it can be considered a cryptic species. The phylogenetic position of C. onobae within Notocotylidae, along with other evidence, highlights the challenges for the taxonomy of the family, for which two major genera appear to be polyphyletic and life cycle data likely undervalued.

Through a continuous survey of trematodes in land snails of Hokkaido, the northernmost island of Japan, we have discovered four species of the genus Brachylaima (Trematode: Brachylaimidae). Among them, Brachylaima ezohelicis, Brachylaima asakawai, and Brachylaima lignieuhadrae have already been described. Each of the three species is a strict specialist in selecting a particular species of land snail as the first intermediate host. In this report, we propose the fourth species, Brachylaima succini sp. nov., based on ecological, morphological, and phylogenetic considerations. Sporocysts and metacercariae of the new species were found exclusively from Succinea lauta, which is known as an amber snail indigenous to Hokkaido. Phylogenetic trees of nuclear 28S rDNA and mitochondrial cytochrome c oxidase subunit 1 (cox1) demonstrated it to be distinct from the other sympatric species. Although metacercariae of the new species possessed unique morphological characters, adult worms experimentally raised from the metacercariae were similar to those of B. ezohelicis and B. lignieuhadrae. Natural definitive hosts of the new species are unknown, but the existence of common cox1 haplotypes from far-distant localities suggests a possibility that birds are involved as the definitive hosts. Findings of amber snails coinfected with both sporocysts of the new species and Leucochloridium perturbatum also support the involvement of birds., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The edible land snail Cornu aspersum, native to the Mediterranean coastlines of North Africa, is widely distributed on most continents and often invasive in areas where introduction is recent. This species could contribute to the geographic spread of parasites as demonstrated for Brachylaima spp. These cosmopolitan trematodes may represent a threat to human health, like in Australia where Brachylaima cribbi infects humans. In this study, we demonstrate for the first time the occurrence of Brachylaima spp. in two French populations of C. aspersum, Thorigné-Fouillard (Ille-et-Vilaine), and Arçais (Deux-Sèvres), with an overall prevalence of 10.4% (Thorigné-Fouillard) and 73.3% (Arçais), respectively and a metacercarial intensity on average three times higher in Thorigné-Fouillard (37) than in Arçais (11). Cornu aspersum may act as a first and second intermediate host, as demonstrated in Arçais. The morphometrics of metacercariae, particularly the great body length about 2 mm, discriminate our Brachylaima species from those already described in C. aspersum (B. cribbi in Australia, and B. aspersae, B. llobregatensis and B. mascomai in Europe). Molecular analysis, based on 28S and COI, suggests the occurrence of two species in our study, one of which is probably Brachylaima mesostoma, an intestinal parasite of passeriform birds described in Central Europe. We underline the need for further research to identify species of Brachylaima in France and measure the health hazard of consuming field-collected snails., (© C. Gérard et al., published by EDP Sciences, 2020.)

The adult and metacercaria life stages of a new species of the microphallid genus Atriophallophorus Deblock & Rosé, 1964 are described from specimens collected at Lake Alexandrina (South Island, New Zealand). In addition to molecular analyses of ribosomal and mitochondrial genes, metacercariae of Atriophallophorus winterbourni n. sp. from the snail host Potamopyrgus antipodarum (Gray) were grown in vitro to characterize internal and external morphology of adults using light and scanning electron microscopy and histological techniques. Atriophallophorus winterbourni n. sp. is readily distinguishable from Atriophallophorus coxiellae Smith, 1973 by having a different structure of the prostatic chamber, sub-circular and dorsal to genital atrium, rather than cylindrical, fibrous, elongate and placed between the seminal vesicle and the genital atrium. The new species is most similar to Atriophallophorus minutus (Price, 1934) with regards to the prostatic chamber and the morphometric data, but possesses elongate-oval testes and subtriangular ovary rather than oval and transversely oval in A. minutus. Phylogenetic analyses including sequence data for A. winterbourni n. sp. suggested a congeneric relationship of the new species to a hitherto undescribed metacercariae reported from Australia, both forming a strongly supported clade closely related to Microphallus and Levinseniella. In addition, we provide an amended diagnosis of Atriophallophorus to accommodate the new species and confirm the sinistral interruption of the outer rim of the ventral sucker caused by the protrusion of the dextral parietal atrial scale at the base of the phallus.

In the context of a broader program dealing with the symbiotic associations of apple snails, we sampled three species that coexist in Lake Regatas (Palermo, Buenos Aires, Argentina). The population of Asolene platae, (but not those of Pomacea canaliculata and Pomacea scalaris) showed trematode larvae (echinocercariae and xiphidiocercariae) in haemocoelic spaces and connective tissue of the digestive gland. The echinocercariae resembled those of the genus Echinochasmus, but lacked sensory hairs on their body and tail; whereas xiphidiocercariae were similar to the xiphidiocercariae armatae belonging to the Opisthoglyphe type. The phylogenetical positions of these trematodes were inferred by the 28S rRNA, ITS1 and mtCOXI gene sequences. The 28S rRNA gene linked the echinocercarial sequences with the polyphyletic genus Echinochasmus (Echinochasmidae), while the xiphidiocercarial sequences were linked with the genus Phaneropsolus (Phaneropsolidae). The molecular markers used were able to distinguish two cryptic molecular entities of the single echinocercarial morphotype. Although ITS1 and mtCOXI did not allow resolving phylogeny beyond the family level because of the scarce number of sequences in the molecular databases, both cercariae (echinocercariae and xiphidiocercariae) could be distinguished by the Internal Transcribed Spacer 1 amplicon size. This is the first correlative morphological and molecular study of zoonotic trematodes in Neotropical ampullariids.

Larval trematodes are the main parasites of snails, and they play a crucial role because they usually castrate their snail hosts and can thus alter their population and community dynamics. This study involved a survey of seven gastropod species (Crepipatella dilatata, Fissurella radiosa, Nacella magellanica, Pareuthria fuscata, Siphonaria lessonii, S. lateralis and Trophon geversianus) parasitized by 12 trematode species (one hemiurid, one gymnophallid, two lepocreadiids, two microphallids, one notocotylid, two renicolids, one philophtalmid, one schistosomatid and one zoogonid) from southern Patagonia (47°S, 65°W), Argentina. Only F. radiosa was free of parasites. The study included the description of five new larvae, based on morphological and molecular information, and a comparison of the parasite diversity with that of a northern locality (42°S, 64°W), characterized by a lower mollusc diversity. Species richness and diversity of parasites were higher in the southern site. This suggests a correlation between the level of parasitism and the diversity of molluscs (first intermediate hosts), which is higher at the high-latitude site and seems to attract shorebirds, which disperse the digenean eggs and facilitate the completion of their life cycles. These results support the notion that parasitism is influenced by large-scale factors such as biogeographical patterns, and small-scale factors such as diversity or abundance of intermediate and definitive hosts.

Data on the life cycles and morphology of the developmental stages of Notocotylus magniovatus, Catatropis vietnamensis n. sp., and Pseudocatatropis dvoryadkini n. sp. were obtained. The Pseudocatatropis genus was restored based on our results. For the studied trematodes, the snails Parajuga spp., Helicorbis sujfunensis (Russia), and Melanoides tuberculata (Vietnam) serve as first intermediate hosts. It has been established that C. vietnamensis n. sp. differs from Catatropis harwoodi and Catatropis pakistanensis in the length of the ridge and metraterm and the location of the anterior papillae. In the life cycle of P. dvoryadkini n. sp., as in Pseudocatatropis joyeuxi, cercariae do not leave the first intermediate host. Both species are very similar in morphometric features, despite the fact that they share no common first intermediate hosts in their life cycles, and the areas of the European and Asian populations of flukes do not overlap. In phylogenetic trees and genetic distances based on the nucleotide sequences of the 28S gene and the ITS2 region of ribosomal DNA, Notocotylus attenuatus, Notocotylus intestinalis, and Notocotylus magniovatus are combined into one systematic group, while C. vietnamensis n. sp. and Catatropis indicus form another group. A third group includes members of different genera: P. dvoryadkini n. sp., and Notocotylus malhamensis, as well as three unclassified Notocotylus spp. The presence in the last group of flukes with three rows of papillae and a median ridge and lateral papillae indicates that these systematic criteria are not determinant in establishing membership of the parasitic worms to one or another genus of Notocotylidae.

Cercariae of digenean family Notocotylidae are characterized by a set of morphological traits which make them easily distinguishable from any other. One of the key features is absence of ventral sucker. This affects basic ways of locomotion and attachment. To understand how these functions are fulfilled we studied musculature arrangement in cercariae of two species by means of fluorescent-phalloidin staining and confocal microscopy. We used Cercaria Notocotylidae sp. No. 11 and 12 Deblock, 1980 from mud snails Ecrobia (=Hydrobia) ventrosa. Information on gross morphology (especially body-tail junction) and basic behavioural patterns of these cercariae is also updated. Major special features of musculature are associated with the ventral concavity: extreme development of dorsoventral muscle fibres and formation of annular arrangement of longitudinal muscle fibres on the ventral side. Additional body-wall and internal muscle bundles in the anterior region are also specific for notocotylid cercariae and seem to play important role in twisting movements during substratum testing. Musculature of dorsal adhesive pockets, oral sucker and tail is also described. These results are discussed in relation to observed locomotory patterns., (Copyright © 2017 Elsevier Ireland Ltd. All rights reserved.)

The metacercariae of Artyfechinostomum malayanum (Leiper, 1911) Mendheim, 1943 were discovered in Pila sp. snails purchased from a market in Phnom Penh, Cambodia. They were isolated from the snails using the artificial digestion technique and were orally fed to 2 hamsters, 1 rat, and 2 mice to obtain the adult flukes. The metacercariae were round, 145-165 μm in diameter, having a cyst wall of 6-10 μm in thickness, a head collar and collar spines, and characteristic features of excretory granules. Adult flukes were recovered in the small intestines of the animals at days 14 and 32 post infection and were morphologically observed using a light microscope and a scanning electron microscope. They were plump or elongated, ventrally curved, 6.0-8.1 × 1.6-2.0 mm in size, and characterized by the head collar bearing 43 collar spines, including 5 end group ones on each side, a long cirrus sac extending beyond the posterior margin of the ventral sucker, a submedian ovary, and 2 deeply lobed testes. Eggs in uteri were operculate, ovoid to ellipsoid, and 120-135 × 68-75 μm in size. In scanning electron microscopy, the head collar was prominent with collar spines looking like horns. Scale-like tegumental spines were densely distributed on the ventral surface between the head collar and ventral sucker. Sensory papillae were distributed mainly on the tegument around suckers. By this study, it has been first confirmed that the life cycle of A. malayanum exists in Cambodia.

The prevalence of cercarial infection in freshwater snails and their evolutionary trends were studied in Nakhon Nayok province, Thailand. A total of 2,869 individual snails were examined for parasitic infections. The results showed that 12 snail species were found to host larval stages of trematodes with an overall prevalence of 4.7%. The infected specimens included 7 types at the cercarial stage; cercariae, megalurous cercariae, echinostome cercariae, furcocercous cercariae, parapleurolophocercous cercariae, virgulate cercariae, and xiphidiocercariae. Regarding molecular identification, ITS2 sequence data of each larval trematode were analyzed, and a dendrogram was constructed using the neighbor-joining method with 10,000 replicates. The dendrogram was separated into 6 clades (order/family), including Echinostomatida/Echinostomatidae, Echinostomatida/Philophthalmidae, Opisthorchiida/Heterophyidae, Plagiorchiida/Prosthogonimidae, Plagiorchiida/Lecithodendriidae, and Strigeatida/Cyathocotylidae. These findings were used to confirm morphological characteristics and evolutionary trends of each type of cercariae discovered in Nakhon Nayok province. Furthermore, this investigation confirmed that the ITS2 data of cercariae could be used to study on phylogenetic relationships or to determine classification of this species at order and/or family level when possible.

Notocotylids are common digeneans parasitising birds and mammals. They have a two-host life cycle with cercariae encysting in the open. Particular life cycles remain unknown for majority of notocotylid species, including a common parasite of sea ducks Tristriata anatis. Here we resolve the life cycle of T. anatis by means of D2 LSU, ITS1 and CO1 DNA sequence analysis, showing that the first intermediate hosts for this species are periwinkles Littorina spp. Morphological descriptions of rediae and cercariae are provided for the first time, and we also supplement the existing morphological data on adults. Apart from differential diagnosis, we discuss some features of cercariae and rediae biology, geographical distribution and host range. Our molecular data confirm that genus Tristriata is monotypic and that T. anatis has circumpolar distribution. CO1 sequence analysis has shown that isolation exists between the Atlantic and Pacific populations of T. anatis, suggesting that there are geographical races. We suppose that their formation may be linked to the Last Ice Age events, when trans-Arctic bird migrations ceased and periwinkle ranges shrunk. These made transfer of parasites across the Arctic impossible, and it still has not resumed. We discuss the possible influence of host vagility and adults' lifespan on digeneans' potential for geographical colonisation.

The microscaphidiid Hexangium sigani Goto & Ozaki, 1929 was found in the intestine of Siganus rivulatus, a siganid fish permanently resident in a lagoon within the mangrove swamps on the Egyptian coast of the Gulf of Aqaba. Intra-molluscan stages of this trematode (mother sporocysts, rediae and cercariae) were found in the gonads and digestive gland of Nassarius pullus (Gastropoda: Nassariidae), a common snail in the same lagoon. Consequently, the life cycle of H. sigani was elucidated under natural conditions: eggs are directly ingested by the snail; mother sporocysts and rediae reach maturity 5-7 and 16-17 weeks post-infection; rediae contain 18-26 developing cercariae; fully developed cercariae are monostome, without penetration glands, emerge from the snail during the night 18-19 weeks post-infection and rapidly encyst on aquatic vegetation (there is no second intermediate host); encysted metacercariae are not progenetic; 2-day-old metacercariae encysted on filamentous algae fed to S. rivulatus developed into fully mature worms 5-6 weeks post-infection. The cycle was completed in about 24 weeks. The intra-molluscan stages are very similar to those of Dictyangium chelydrae Stunkard, 1943, the only described intra-molluscan stages of any microscaphidiid. However, they are also similar to those of the family Mesometridae. The present study of H. sigani describes the first complete microscaphidiid life cycle, and implicitly supports the phylogenetic relationship of this family with the Mesometridae inferred from molecular phylogenetic studies.

The life cycle of Neocladocystis intestinalis (Vaz, 1932) was resolved experimentally. The prosobranchiate snail Aylacostoma chloroticum Hylton Scott (Thiaridae) collected in the Yacyretá Dam, Province of Misiones, Argentina, was found naturally infected with cercariae that possessed pigmented eye spots, 7 pairs of penetration glands, 12 pairs of flame cells, and a V-shaped, or Y-shaped excretory vesicle with very short stem. The cercariae developed in oval cysts, which were found on fin rays, and under scales of naturally and experimentally exposed tetragonopterid fish species and of experimentally exposed poecilid and prochilodont fish species. Adults were obtained experimentally from juvenile Salminus brasiliensis (Characidae), bred in captivity, and infected with metacercariae from albino Gymnocorymbus ternetzi (Tetragonopteridae), which had been exposed to emerging cercariae.

In order to obtain a comprehensive understanding of trematode diversity in Bithynia siamensis goniomphalos sensu lato, the first intermediate host of the liver fluke Opisthorchis viverrini s.l., the prevalence of larval trematode species was investigated in different localities in Thailand and Lao People's Democratic Republic (Lao PDR). In Thailand, snail samples were collected from 29 localities in the nine provinces: Buri Ram, Surin, Chaiya Phum, Maha Sarakham, Khon Kaen, Kalasin, Mukdahan, Sakon Nakhon and Nakhon Phanom. In Lao PDR, snail samples were collected from 21 localities in Vientiane Province and six localities in Savannakhet Province. Snails were identified by standard morphological criteria and then examined for trematode infection using the cercarial shedding method. Twenty different types of cercariae were detected and identified, based on morphological criteria. Virgulate type 1 emerged as the most common cercaria, with an average prevalence of 10.90% (range 0.26-54.22%) in Thailand and 6.58% (range 1.15-89.77%) in Lao PDR. Opisthorchis viverrini s.l. cercariae were the fourth most common in Thailand, with an average prevalence of 1.59% (0.15-6.93), while in Lao PDR their prevalence was 0.96% (0.08-8.37). The high diversity of trematode cercariae observed in this study indicates that B. s. goniomphalos s.l. is highly susceptible to infection with a variety of trematode species. However, the role of non-opisthorchiid trematodes as fish-borne parasites in human health is not fully known and further molecular identification is required.

We describe Proterometra ariasae n. sp. based upon cercariae shed from a freshwater snail, Pleurocera sp., and adults infecting the buccal cavity of longear sunfish, Lepomis megalotis, captured from the Chickasawhay River, Mississippi, USA. We also provide supplemental observations of cercarial and adult paratypes of Proterometra autraini from the Au Train River, Michigan, USA. Sequence data for the ribosomal internal transcribed spacer 2 (ITS2) from adults and cercariae of the new species were identical. Adults of the new species differ from congeners by having (i) a markedly large body, (ii) a proportionally large oral sucker, (iii) ovoid testes, (iv) a strongly muscular and laterally expanded pars prostatica, (v) a uterus that is extensively convoluted between the ovary and ventral sucker (vi) and a vitellarium as long as the caeca and extending posteriad beyond the anterior margin of the testes. Cercariae of the new species differ from those of its congeners by having (i) a tail stem that is shorter than 10mm and that lacks a medial constriction, (ii) obcordate furcae that are wider than long, (iii) mamillae distributed throughout the anterior tail stem only, and (v) a proportionally small distome that has relatively few uterine eggs and remains withdrawn in the anterior tail stem region in actively swimming cercariae. This is the first report of Proterometra from Mississippi, the second description to employ morphology and sequence data to elucidate a life cycle for Proterometra, and the third species of Proterometra from an intermediate host not assigned to Elimia., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

The aim of this study was to determine the presence and prevalence of larval stages of Dicrocoelium dendriticum and Brachylaima sp. in the first intermediate host, a species of land snail, Helix aspersa, in Turkey. A total of 211 snails were collected in April-May 2014 from pastures in Mersin District. Larval stages of D. dendriticum were identified under a light microscope. Hepatopancreas from naturally infected H. aspersa snails were examined histologically. The prevalence of larval stages of D. dendriticum and Brachylaima sp. in H. aspersa snails was found to be 2.4% and 1.9%, respectively, in Mersin, Turkey. Cercariae were not matured in sporocysts at the beginning of April; however, it was observed that cercariae matured and started to leave sporocysts by early-May. Thus, it was concluded that H. aspersa acts as an intermediate host to D. dendriticumin and Brachylaima sp. in Mersin, Turkey. A digenean trematode Brachylaima sp. was seen for the first time in Turkey.

In central Mexico, populations of the freshwater snail Physella cubensis were infected with metacercariae from a species of Echinoparyphium (Digenea: Echinostomatidae). In the current study, we describe both larval and adult stages of this species obtained from experimental and natural infections. A total 180 snails were collected from Patzcuaro Lake, Michoacan state in central Mexico in July 2012. In the laboratory snails were placed in individual vials and exposed to light with the aim of observing emergence of cercariae. To obtain metacercariae, uninfected snails (P. cubensis) were exposed to cercariae. Chicks were infected with metacercariae to obtain adults. Nine days post-infection, eggs were recovered and incubated in tap water at room temperature to observe miracidia. Adults obtained from natural and experimentally infected hosts possess a head collar with 45 spines in two alternating rows, confirming the identification as Echinoparyphium recurvatum von Linstow 1873. To test the conspecificity of all stages, sequences of nuclear internal transcribed spacer 1 (ITS1), 5.8S and ITS2 rDNA were obtained from two adult worms recovered from chicks and also a natural avian host, the shoveler duck Anas clypeata, together with five cercarial and four metacercarial isolates from nine snails. The genetic divergence estimated among the 13 isolates was very low, ranging from 0 to 0.6%. Phylogenetic analyses inferred by maximum likelihood and Bayesian methods showed that all isolates of E. recurvatum form a single clade with strong support. The presence of E. recurvatum in P. cubensis and A. clypeata from central Mexico represents new host reports, and extends the distribution range in the Americas.

Littorinid snails are one particular group of gastropods identified as important intermediate hosts for a wide range of digenean parasite species, at least throughout the Northern Hemisphere. However nothing is known of trematode species infecting these snails in the Southern Hemisphere. This study is the first attempt at cataloguing the digenean parasites infecting littorinids in New Zealand. Examination of over 5,000 individuals of two species of the genus Austrolittorina Rosewater, A. cincta Quoy & Gaimard and A. antipodum Philippi, from intertidal rocky shores, revealed infections with four digenean species representative of a diverse range of families: Philophthalmidae Looss, 1899, Notocotylidae Lühe, 1909, Renicolidae Dollfus, 1939 and Microphallidae Ward, 1901. This paper provides detailed morphological descriptions of the cercariae and intramolluscan stages of these parasites. Furthermore, partial sequences of the 28S rRNA gene and the mitochondrial gene cytochrome c oxidase subunit 1 (cox1) for varying numbers of isolates of each species were obtained. Phylogenetic analyses were carried out at the superfamily level and along with the morphological data were used to infer the generic affiliation of the species.

Cornu aspersum (= syn. Helix aspersa ) snails imported into NE Spain from Algeria and South Africa, and intended for human consumption via sale in public markets, were analyzed to assess their contribution to geographic dissemination of Brachylaima species. Prevalence and viability studies of metacercariae were performed on Algerian and South African Brachylaima adults. Morphometric studies were performed by measuring 16 variables in metacercariae and 18 variables in adults. Principal component analyses (PCA) were performed to assess the contribution of each variable in the separation of the different groups. A MANOVA test performed on morphometric data from Brachylaima llobregatensis and Brachylaima mascomai Algerian and South African adults, revealed a significant multivariate main effect (P < 0.001) and univariate effects in 13 variables (P ≤ 0.001). Pairwise comparisons revealed significant differences in 13 variables between B. mascomai and Algerian adults, as opposed to 3 variables (testis I width, testis II width, and egg width) when compared with B. llobregatensis. South African adults had significant differences in 5 variables (body length, oral sucker length, oral sucker width, egg length, and egg width) when compared with B. llobregatensis, as opposed to 1 variable (testis II width) when compared with B. mascomai. Results from PCA showed 2 different groups: B. llobregatensis/Algerian adults (overlapped) and B. mascomai/South African adults (overlapped). Imported edible C. aspersum specimens can contribute significantly to the geographic spread of Brachylaima species by harboring infective metacercariae which could easily infect animals, given their heteroxenous character. Brachylaima llobregatensis has previously been detected in NE Spain only, and now this species appears to be parasitizing C. aspersum in Algeria (North Africa). This geographic dispersion could be favored by commerce in terrestrial snails such as C. aspersum.

Larval stages of Plagiorchis spp. are both ubiquitous and ecologically important parasites in snail populations of freshwater ecosystems in Europe. However, difficulties in distinguishing the morphologically similar cercariae used for species identification, may lead to underestimation of species diversity. In this study, 38 isolates of Plagiorchis spp. infecting two lymnaeid snails, Lymnaea stagnalis (L.) and Radix auricularia (L.), in five central European freshwater ecosystems were subjected to morphological and molecular assessment. Five morphologically homogeneous and genetically distinct lineages of Plagiorchis spp. were identified via matching molecular data for the mitochondrial cytochrome c oxidase subunit I (cox1) gene with detailed morphological and morphometric data of the cercariae. Comparative sequence analysis using partial 28S rDNA and ITS1-5.8S-ITS2 sequences revealed that three distinct cox1 lineages are conspecific with Plagiorchis elegans (Rudolphi, 1802), P. maculosus (Rudolphi, 1802) and P. koreanus Ogata, 1938, respectively, whereas the lineage identified based on cercarial morphology as P. neomidis Brendow, 1970 plus a single isolate that could not be assigned to a described species, did not match any of the available sequences for Plagiorchis spp. A key to the cercariae of Plagiorchis spp. parasitising lymnaeid populations in central Europe is provided to facilitate identification.

This manuscript describes the daughter parthenitae (sporocysts) and cercariae of two species of renicolid xiphidiocercaria that infect the California horn snail, Cerithidea californica, which serves as first intermediate host for a diverse and ecologically important guild of digenean trematode parasitic castrators. The two species described here have previously been considered to be a single morphospecies in ecological and evolutionary research. We provide provisional species names to respect that digenean alpha taxonomy is currently focused on sexual (adult) stages, while simultaneously respecting the spirit and utility of formal nomenclature in providing unambiguously unique, species-level names that also clarify to the extent possible species' taxonomic affiliations. The first species, Renicola sp. "polychaetophila" is most readily distinguishable from previously described renicolid xiphidiocercariae by a combination of (1) having a penetration gland duct arrangement of 2[(1+3+1)+1], (2) having one pair of penetration glands positioned anteriorly to the main gland cluster, (3) lacking tegmental spines, and (4) infecting Cerithidea californica. The second species, Renicola sp. "martini", is most readily distinguishable from other renicolid xiphidiocercariae that also have tegmental spines by a combination of (1) having a simple, bullet-shaped oral stylet sclerotized for 50-80% of its length, (2) having a cystogenous-gland field with an anterior-most extent about half way between the oral and ventral suckers, and (3) in infecting Cerithidea californica. Phylogenetic analyses using DNA (COI and ITS1) sequence data support that these two trematodes represent distinct species of Renicola. We also (1) provide an emended diagnosis for renicolid cercariae, (2) highlight a few morphological characters that may be useful for future taxonomic work involving renicolid xiphidiocercariae, and (3) suggest that future descriptive work involving trematode parthenitae include more information pertaining to the group of parthenitae as a whole.

We elucidate the life cycle of Maritrema orensense for the first time and experimentally confirm that of the sympatric Maritrema bonaerense. In Argentinean estuaries, both species parasitize the cochliopid snail Heleobia australis as first intermediate host, the grapsid crabs Neohelice granulata and Cyrtograpsus angulatus as second intermediate hosts, and gulls as definitive hosts. Here, we describe the daughter sporocysts and cercariae of M. orensense and redescribe these stages for M. bonaerense. Sporocysts of M. orensense are shorter, with fewer developed cercariae than M. bonaerense. The cercariae of M. orensense have longer, larger, and more undulating cephalic glands than M. bonaerense. We redescribe metacercariae and adults of both species and compare them with the previous descriptions. Intestinal ceca length, vitellaria shape and extension, and egg size are the most relevant characteristics in metacercariae and adults for differentiating the species. Hence, the detailed morphological description and comparative analyses of morphometrics obtained from natural and experimental infections permit clear differentiation of M. orensense and M. bonaerense at each life stage.

Animals living in colonies or collectives composed of highly-related individuals often produce morphs that are physically and behaviourally specialised to perform specific tasks. Because such morphs are often sterile, their production represents a fitness cost for the colony and there should be an optimal ratio of the numbers of sterile specialists and reproductive members that may be adjustable to environmental conditions. Trematode parasites undergo asexual multiplication within their snail intermediate host, resulting in large numbers of clonal stages known as rediae or sporocysts, depending on the trematode species. In areas with high prevalences of infection, the host can be infected by multiple species, which can lead to intense competition for limited resources. Here, we describe the existence of specialised 'mini-rediae' in the trematode Philophthalmus sp. that are morphologically and functionally specialised for interspecific competition. Mini-rediae were observed feeding on the sporocysts of a co-occurring trematode species -Maritrema novaezealandensis. In addition, in larger snails - which are less likely to have M. novaezealandensis infections -Philophthalmus sp. produces relatively fewer mini-rediae than expected. Our findings support results from a prior study which demonstrated the existence of morphs that perform specialised functions in antagonistic interspecific interactions in trematodes, and additionally shows that the number of these morphs in each host is associated with the likelihood of encountering other species within the same host. Trematodes may thus provide interesting models for studying morphological specialisation in colonial organisms., (Copyright © 2011 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

The subject of the following study was the natural and experimental invasion of trematode larvae in Potamopyrgus antipodarum from Bory Tucholskie National Park (Poland). Only one out of the 14,908 dissected specimens had oval sporocysts and mature cercariae of fish fluke, which belongs to the Sanguinicolidae family. It is the first recorded case in the European population of P. antipodarum living in inland water. The experimental study showed the possibility of native metacercariae (Echinostoma revolutum, Echinoparyphium aconiatum and Hypoderaeum conoideum) settlement in those immigrant snail species; however, exposure to parasites resulted in an increase in snail mortality. The three out of six used cercariae species were able to transform into metacercariae in P. antipodarum as in the second intermediate host, but the exposure to parasitic larvae of four of the used species resulted in an increase in snails' mortality. It may suggest that not only metacercariae settlement but also the attack of cercariae (Rubenstrema opisthovitellinum at a temperature of 22 degrees C) affected the low survival of experimental snails in comparison to control animals. The subject of discussion presented in this paper is also the hypothesis on probable effect of the interaction between P. antipodarum and native snail species (as a source of invasive larvae of parasites) living in the same habitat.

Out of 328 specimens of the land snail Monacha obstructa, 105 (32%) were infected with a new metacercaria belonging to the genus Brachylaima Dujardin 1843. The present snail is considered as a new host for this parasite in Egypt. Morphological and morphometric patterns were elucidated. Number of recovered infective metacercariae ranged between 4-35 per kidney of snail host. Metacercariae inhabited only the kidney of infected snails. Total length of mature metacercariae ranged from 1800mu-2050mu (1940mu). The anterior extremity is dome shaped and ceca were highly expanded, undulating, and filled with masses of brown cells and renal tissues. Metacercariae were fully mature, unencyted and highly active. They were either roaming in pathways inside the kidney or firmly anchored to renal tissues via oral sucker. Oral sucker length/total body length is 1:8.5. The histopathological effects involved disintegration of renal lamellae and formation of numerous necrotic masses. Invading metacercariae faced no host resistance and they were surrounded by a parasitovorus vacuole as a mean of immune-evasion. SEM studies revealed that dorsal surface of ventral sucker area is covered with rows of minute spines, Oral suker also is provided with a median tongue-like shaped septum. The rest of integument is aspinose. A critical review for relevant metacercariae of genus Brachylaima is provided.

A survey of the larval stages (cercariae and metacercariae) of trematodes (Digenea) found in planorbid snails in Central Europe (Austria, Czech Republic, south-east Germany, Hungary, Poland and the Slovak Republic) is presented based on a study of 7,628 snails of 12 species examined between 1998-2006. A total of 34 trematode larval stages, comprising cercariae of 28 species and metacercariae of seven species (one species occurred both as cercaria and metacercaria) of nine families were found in 898 (11.5%) snails of eight species. The dominant cercariae were those belonging to the Rubenstrema exasperatum (Rudolphi, 1819)/Neoglyphe locellus (Kossack, 1910) species complex, Tylodelphys excavata (Rudolphi, 1803) and Echinostoma spiniferum (La Valette, 1855) sensu Nasincová (1992), all from Planorbarius corneus (Linnaeus). Almost the same spectrum of cercariae of the families Echinostomatidae, Plagiorchiidae and Omphalometridae was found in the present study as in previous reports; however, a considerably lower spectrum of cercariae of the families Diplostomidae and Strigeidae was recorded. The most frequent metacercariae were those of Echinoparyphium aconiatum Dietz, 1909, Neoglyphe locellus and Moliniella anceps (Molin, 1859), all occurring mainly in P. corneus. The most heavily infected snail species was P. corneus, followed by Planorbis planorbis (Linnaeus) and Segmentina nitida (Müller). The widest spectrum of trematode species was found in P. planorbis and P. corneus. Forty-two cercariae identified to the species level belonging to 15 families, plus an additional 43 taxa recorded under generic or provisional names, were reported from 11 species of planorbids in previous studies carried out in Central Europe. However, the actual number of trematode species occurring in the planorbid snails is probably much lower, because many, if not most, larval stages reported under provisional names or unidentified to the species level may be conspecific with identified adult forms. A key to the cercariae and metacercariae recorded from planorbids in Central Europe, together with illustrations of those species encountered most frequently in the field, is provided to facilitate identification.

In eastern Asia and western North America at least nine morphologically distinguishable species of digenean trematode infect the mud snail, Batillaria attramentaria (Sowerby 1855) (=B. cumingi (Crosse 1862)), as first intermediate host. Further, molecular and morphological evidence indicates that several of these trematode species comprise complexes of cryptic species. I present an identification key to these nine trematode morphospecies (including four newly reported species). Additionally, I provide an annotated list, which includes further diagnostic information on the larval stages (cercariae, parthenitae, and metacercariae), information on second intermediate host use, links to the previous relevant reports of trematodes infecting B. attramentaria and notes on other aspects of the species' biology.

The freshwater snail family Thiaridae was studied at five different locations: water sources for the Khek River, Thailand. Snail samples were collected by hand using counts per unit of time sampling method between December 2004 and October 2005. The physico-chemical quality of the water changed with the seasons and affected the sampling areas during both the dry season and the flood season. A total of 9,568 snail samples comprised of 14 species were found. These were 284 Tarebia granifera, 24 Melanoides tuberculata, 86 Thiara scabra, 3,295 Paracrostoma pseudosulcospira pseudosulcospira, 736 P. paludiformis paludiformis, 3,266 P. paludiformis dubiosa, 117 P. morrisoni, 304 Brotia (Brotia) binodosa binodosa, 1,250 B. (Brotia) microsculpta, 146 B. (Senckenbergia) wykoffi, 1 B. (Brotia) pagodula, 5 B. (Brotia) binodosa spiralis, 5 B. (Brotia) insolita and 49 B. (Brotia) manningi. The cercariae were investigated using shedding and crushing methods where they were categorized into two types and five species. The first type, Parapleurolophocercous cercariae, were comprised of Haplorchis pumilio Looss, 1899 and Centrocestus formosanus Nishigori, 1924. The second type, Xiphidiocercariae were comprised of Acanthatrium hitaense Koga, 1953, Loxogenoides bicolor Kaw, 1945 and Haematoloechus similis Looss, 1899. The cercarial infection rates in the above 5 species were 0.1% (5:9,568), 0.2% (15:9,568), 0.3% (24:9,568), 0.4% (37:9,568) and 0.1% (5:9,568), respectively. Five species of snails were susceptible to trematode infections. They were T. granifera, M. tuberculata, T. scabra, P. paludiformis paludiformis and B. (Senckenbergia) wykoffi; infections were found in 26.1% (74:284), 33.3% (8:24), 1.2% (1:86), 0.3% (2:736) and 0.7% (1:146), respectively.

Cercaria sevillana is the cercaria larval stage that infects the gonads and the digestive gland of its first intermediate host, Nassarius reticulatus. In this study the decapodous crustacean Carcinus maenas was used to determine if it would serve as second intermediate host in the parasite's life cycle. The latter hypothesis was based on the knowledge that C. maenas is the second intermediate host of several other digenean species. After dissection, it was possible to observe encysted metacercariae in the antennal glands of the green crab. After biochemical excystment, the metacercariae were processed for light and scanning electron microscopy. The morphological features observed led us to conclude that this species was a microphallid fluke, and it was identified as Gynaecotyla longiintestinata. To establish a possible relationship between C. sevillana and this metacercariae, the ITS1 region was analyzed. Thus, DNA was extracted from C. sevillana and from the cysts isolated from the antennal glands. The ITS1 region was amplified and sequenced, and the alignment clearly demonstrated that the cercaria and the metacercariae belonged to the same species, G. longiintestinata.

Infection by intramolluscan stages of Microphallus breviatus Deblock & Maillard, 1975 are common in Hydrobia ventrosa mudsnails in Iceland. Cercariae encyst inside the daughter sporocysts and develop there into metacercariae that become infective for the definitive hosts which are probably charadriiform waders. The adult stage was obtained in 1-day-old chicks that were experimentally infected with metacercariae from naturally infected hydrobians. New data are presented on the morphology and biology of the cercariae, and the adult is described for the first time. Comparisons are made between M. breviatus and closely related species. Differential diagnosis of M. breviatus is given. The morphological specializations in larvae of the hermaphroditic generation of the microphallids accompanying transition from trixenous life cycles to dixenous ones are considered, and the applicability of the term "life-cycle truncation" to microphallids with dixenous life cycles is discussed. Also, reasons for the broad distribution of dixenous life cycles within the family Microphallidae are reviewed.

As a result of experimental and faunistic investigations it is established that the development of the trematode species Azygia hwangtsiytii Tsin, 1933 in Primorsky Territory is realized in the first intermediate host, snail Cipangopaludina ussuriensis, and in second hosts, fishes Perccottus glehni and Channa argus warpachowskii, which can serve as transit, as well as final hosts. For Azygia robusta Odhner, 1911 terms of the development in the first intermediate host, snail Anisus centrifugus are established.

Cercariae belonging to the genus Philophthalmus (Digenea: Philophthalmidae) were detected in a freshwater snail Semisulcospira libertina collected from Innai Town, Oita Prefecture, Kyusyu, Japan. This is the first record of the cercaria of this genus from East Asia and from Semisulcospira. Daughter rediae and cercariae are briefly described and morphologically compared with similar but unidentified ones reported from Japan. Cercariae were found encysting on the surface of the bottom of the container and metamorphosed into a flask-like metacercaria characteristic of Philophthalmus.

This study of infection of southern Australian land snails with Brachylaima cribbi metacercariae has shown that all commonly encountered native and introduced snails are susceptible second intermediate hosts. The range of infected snails is extensive with metacercariae-infected snails being present in all districts across southern Australia. C. virgata has the highest average natural metacercarial infection intensity of 6.1 metacercariae per infected snail. The susceptibility of birds, mammals and reptiles to B. cribbi infection was studied in South Australia by capturing, dissecting and examining the intestinal tract contents of animals which commonly eat land snails as a food source. Indigenous Australian little ravens (Corvus mellori), which are a common scavenger bird, and two other passeriform birds, the black bird (Turdus merula) and the starling (Sturnus vulgaris), which are both introduced European birds, were found to have the highest infection rates of all animals examined. Other birds found infected with B. cribbi were an emu (Dromaius novaehollandiae), chickens (Gallus gallus) and a pigeon (Columba livia). Natural infections were also detected in field mice (Mus domesticus) and shingleback lizards (Tiliqua rugosa) although the intensity of infection was lower than that observed in birds. Susceptibility studies of laboratory mice, rats and ducks showed that mice developed patent infections which persisted for several weeks, rats developed a short-lived infection of three weeks' duration and ducks did not support infection. This study has shown for the first time that a brachylaimid can infect a wide host range of birds, mammals and reptiles in nature.

In contrasts to formerly known data, it is found that two species of the Parasymphilodora trematodes, Parasymphilodora japonica (Yamaguti, 1938) and P. markewitschi (Kulakowskaja, 1947) are actually distributed in the territory of Primorye land. The first intermedial hosts of the former species are snails of the genus Parafossarulus; in the second species, these hosts are snails of Boreoelona. A life cycle and stages of development of both trematodes are described.

Diplostomoid digenean metacercariae have caused widescale mortalities of channel catfish, Ictalurus punctatus (Rafinesque), at aquaculture farms in Louisiana, Mississippi and Arkansas, USA. Originally, based on a tentative diagnosis, the industry considered the primary harmful agent to be an introduced species from Europe, Bolbophorus confusus (Krause, 1914), frequently reported from the American white pelican, Pelecanus erythrorhynchos Gmelin. Our group has now shown, using ITS 1-2 plus three more-conservative gene fragments, that two sympatric species of Bolbophorus exist in the American white pelican. One, B. damnificus Overstreet et Curran, 2002, infects the musculature of catfish, and the other, probably not B. confusus, does not infect catfish. However, at least four other pathogenic diplostomoids and a clinostomoid infect the catfish, and they use at least four different snail hosts, including the planorbids Planorbella trivolvis (Say) and Gyraulus parvus (Say), the physid Physella gyrina (Say) and a lymnaeid. Two metacercariae, B. damnificus and Bursacetabulus pelecanus Dronen, Tehrany et Wardle, 1999, infect the catfish and mature in the pelican; two others, Austrodiplostomum compactum (Lutz, 1928) and Hysteromorpha cf. triloba (Rudolphi, 1819), mature in cormorants; one, Diplostomum sp., matures in seagulls and at least one, Clinostomum marginatum (Rudolphi, 1819), matures in herons, egrets and other wading birds. Consequently, management of catfish ponds relative to digenean infections requires considerable biological information on the fish, bird, and snail hosts as well as the parasites.

Metacercariae of Cyathocotyle bushiensis Khan, 1962 (Digenea) were found in populations of seven species of gastropod snails collected from lakes and rivers in the south of West Siberia (Russia). This is the first record of C. bushiensis in Russia. Five species of snails, Lymnaea stagnalis, L. palustris, L. tumida, Planorbis planorbis (Pulmonata) and Viviparus viviparus (Prosobranchia) were recorded as new hosts for the metacercariae of C. bushiensis. The infection rate of Bithynia tentaculata and Opisthorchophorus (= Codiella) troscheli (Prosobranchia), the main hosts of C. bushiensis metacercariae, was analyzed in regard to the sex and shell length of molluscs. It was revealed that infection rate and mean intensity of metacercariae increases with the shell lengths. Drawings and descriptions of excysted metacercariae from naturally infected snails and adult worms from experimentally infected domestic ducklings are given.

Transmission of Leucochloridium species to their definitive avian hosts may be facilitated by the rhythmic movement of coloured sporocyst broodsacs in the ocular tentacles of infected snails. These broodsacs resemble caterpillars and by enticement increase the probability of predation by birds. Broodsac banding pattern and colour (green, yellow to red/brown) have traditionally formed part of the taxonomic criteria for the genus. In this study, sequence divergence of the 5.8S rDNA gene and associated internal transcribed spacers (ITS1 and ITS2) in two of the most frequently observed Leucochloridium taxa from Europe is related to broodsac type based on colour and banding pattern. The present green-banded broodsac (L. paradoxum Carus, 1835) and brown-banded broodsac forms (L. variae McIntosh, 1932) differ in ITS sequence by 6.8%, confirming their distinctness. No intraspecific differences were noted within each colour morph in specimens collected from Poland, Denmark or Norway, indicating that a single taxon of each type occurs in Europe. The significance of these findings to our understanding of metapopulation dynamics and evolutionary ecology of Leucochloridium is discussed.

Description of a life cycle and development stages of a trematode Holostephanus nipponicus Yamaguti, 1939 is given. Experimental studies have shown that in Primorye, the first intermediate host is commonly a snail Parafossarulus spiridonovi, and the second hosts are freshwater fishes Rhodeus sericeus sericeus and Pseudorasbora parva. Adult worms H. nipponicus were reared in a chicken.

Paludomus petrosus, the freshwater snails found in Pa La-U Waterfall, were examined for cercarial infection of trematodes. The snails were collected every other month from April, 2001 to February, 2002. Collections were taken from two sampling stations. The counts per unit of time' method was used for collection of the snails. The density of snails was highest in June 2001, and the highest of parasite infection rate was in February 2002. Four types of cercariae were found in the snails: Xiphidiocercariae, Amphistome, Furcocercous cercariae type I, and Furcocercous cercariae type II. Xiphidiocercariae were found in April 2001 to February 2002. Amphistome, Furcocercous cercariae type I and Furcocercous cercariae type II were found in February 2002.

Descriptions of the miracidium, mother redia, daughter redia, grandaughter redia, cercaria, metacercaria and adult stages of Philophthalmus gralli Mathis and Leger, 1910 recovered from experimental infections are presented. The intermediate host, Melanoides tuberculata, was collected from freshwater rivulets in Aguasanta and Yaguracual, Sucre State, Venezuela. Chicken were orally infected with cercariae and metacercariae, and metacercariae were introduced directly into the eyes by pipette. Both processes of infection produced adult worms. This is a new geographical record for P. gralli.

A cystophorous cercaria obtained from Semisulcospira libertina (Gould) from Tobihino, Nara, Honshu, Japan, was used to experimentally infect a freshwater goby Rhinogobius sp. OR via the copepods Mesocyclops leuckarti (Claus), Thermocyclops hyalinus (Rehberg), and Eucyclops sarrulatus (Fisher). It was shown to grow into Genarchopsis goppo Ozaki, 1925. The parasite was found to occur as a natural infection in the stomach of Rhinogobius sp. OR and Odontobutis obscura (Temminck and Schlegel) from Tobihino.

The fauna of digenean daughter-sporocysts, rediae, cercariae and metacercariae infecting molluscs Littorina spp., Onoba aculeus. Nucella lapillus and Epheria vincta has been studied in the Skerjafjordur and Grindavik regions of SW Iceland. In total, intramolluscan stages of 19 digenean species were recorded; 14 of them are new for Iceland and one of them, a microphallid named Cercaria islandica I, was unknown. A description of this new microphallid cercaria is provided. In addition, the identification and separation of the intramolluscan stages of some microphallid, renicolid and echinostomatid species are discussed. Consideration is given to difficulties encountered when identifying digenean species found on the coasts of European countries. Problems have arisen largely because larval and adult stages have been described and named independently and in isolation, synonyms are common and many "definitive" descriptions are inadequate or incomplete.