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Clinostomids are a group of digeneans in which substantial diversity has been recently discovered, with some metacercariae specific to their fish hosts. Genetic analysis has been instrumental in elucidating species diversity within this genus. Recently, seven COI lineages were reported in Argentina, along with three metacercarial morphotypes lacking molecular data. Two of these were found parasitising Rivulidae fishes. The discovery of Clinostomum metacercariae in Trigonectes aplocheiloides and Titanolebias monstrosus from temporary ponds in the western Chacoan region allowed us to redescribe the metacercariae previously identified by other authors and provide the first sequences of this lineage. The morphology of the metacercariae in both hosts matched previously reported descriptions. Genetic analysis clustered the new lineage with Clinostomum detruncatum , Clinostomum sp. 7, Clinostomum L1, and Clinostomum CRA. This discovery leaves only two morphological records of metacercariae to be characterised using DNA sequencing: one in another Rivulidae ( Neofundulus paraguayensis ) and one in a Loricaridae ( Hypostomus sp.). The present results represent the eighth clinostomid lineage sequenced from Argentina, highlighting the extensive diversity in South America and the many lineages yet to be described or identified, considering that only one of these lineages is formally described based on adult specimens found in the heron Ardea cocoi.

In this study, we describe a new species of Pseudoparacreptotrema (Allocreadiidae) from the mugilid Dajaus monticola collected in western Puerto Rico, where no allocreadiid has previously been reported, bringing the number of species in this genus to seven (five in D. monticola , two in Profundulus spp.). The new parasite species is distinguished from congeners by its overall size, oral-to-ventral sucker size ratio, pharynx size, cirrus sac, and oral lobe morphology, and by 0.64%-3.45% divergence in a 1019-bp alignment of 28S. We build on prior suggestions that the current concept of P. agonostomi likely includes multiple species and provide the first mitochondrial data (whole mitochondrial genome) as well as the complete nuclear rDNA array from Pseudoparacreptotrema to facilitate future phylogenetic work. Within the Allocreadiidae, phylogenetic analysis of mitochondrial genomes and 28S provides conflicting topologies for the placement of Pseudoparacreptotrema and Allocreadium. The 28S phylogeny of six species of Pseudoparacreptotrema resembles that of four lineages of D. monticola in that in both host and parasite, Pacific coastal lineages branch earliest, and a Caribbean lineage is more recently evolved.

Diplomonorchis micropogoni Nahhas & Cable, 1964 was considered a junior subjective synonym of Diplomonorchis leiostomi Hopkins, 1941 in 1969. Diplomonorchis leiostomi has since been widely reported from the coastal Western Atlantic between Delaware Bay and southern Brazil. Until now, taxonomically verifiable DNA sequence data for D. leiostomi has been available from an individual worm collected from the northern Gulf of Mexico. We generated a partial sequence of the 28S rRNA gene from D. leiostomi from the spot croaker, Leiostomus xanthurus Lacepède (type-host) from Beaufort, North Carolina, USA (type-locality) that differed at 31 of 1,246 bases from the available 28S sequence. This prompted a reevaluation of Diplomonorchis spp. identities from the northern Gulf of Mexico. We found D. leiostomi and D. micropogoni distinguishable by testes shape and size, and to a lesser degree by relative caecal length. Museum specimens of D. leiostomi, identified from the Gulf of Mexico represent a species complex containing D. leiostomi, D. cf. micropogoni and, a new species of Diplomonorchis. The sequences previously identified as D. leiostomi in GenBank (AY222137 & AY222252) are herein identified as D. cf. micropogoni. The new species is described from newly collected material herein. Phylogenetic analysis of 28S rRNA sequences from the species complex plus 46 species from the Monorchioidea Odhner, 1911 indicated all three Diplomonorchis spp. are closely related and form a clade with some species of Lasiotocus Looss, 1907. With the addition of the new species, and acceptance of D. micropogoni, there are currently 14 valid species in Diplomonorchis., Competing Interests: Declarations Conflict of interest All authors report no competing interest or conflict related to the research or writing. Ethical approval Auburn University institutional guidelines for care and use of animals were followed. Fish were collected under permits issued from the Mississippi Department of Marine Resources, Alabama Department of Conservation and Natural Resources Marine Division, and the Florida Fish and Wildlife Conservation Commission Division of Marine Fisheries Management, Special Activity License SAL-10-15-0942-SR., (© 2024. The Author(s).)

Three new species of Gyrodactylu s were identified from the body surface of the Triplophysa species from the Qinghai-Tibet Plateau, Gyrodactylus triplorienchili n. sp. on Triplophysa orientalis in northern Tibet, G. yellochili n. sp. on T. sellaefer and T. scleroptera and G. triplsellachili n. sp. on T. sellaefer and T. robusta in Lanzhou Reach of the Yellow River. The three newly identified species share the nemachili group species' characteristic of having inturning hamulus roots. Gyrodactylus triplorienchili n. sp. shared a quadrate sickle heel and a thin marginal hook sickle, two morphological traits that set them apart from G. yellochili n. sp. However, they may be identified by the distinct shapes of the sickle base and marginal hook sickle point. Gyrodactylus triplsellachili n. sp. had much larger opisthaptoral hard part size than the other two species. The three new species show relatively low interspecific differences of 2.9-5.3% p-distance for ITS1-5.85-ITS2 rDNA sequences. Phylogenetic analysis indicated that the three new species formed a well-supported monophyletic group (bp = 99) with the other nemachili group species.

We described Creptotrema cambeve n. sp. from the intestine of the Brazilian catfish Cambeva davisi (Haseman, 1911) (= Trichomycterus davisi ) based on integrative analyses using morphological and molecular approaches. Creptotrema cambeve n. sp. closely resembles morphologically Creptotrema paraense Vicente, Santos & Souza, 1978, which was described from a siluriform fish in Northern Brazil; however, the two species differ mainly in the oral and ventral sucker sizes and the distribution of the vitellaria. The phylogenetic analyses of the 28S rDNA placed the sequences of the new species in a monophyletic clade together with all other Creptotrema spp. and as sister taxon of Creptotrema cruste Alcantara, Ebert, Ferreira-Silva, Forti, Morais, Pérez-Ponce de León & Silva, 2024, a parasite from a Brazilian anuran. Genetic divergences between the new species and other Creptotrema spp. varied from 0.2% to 4.3%, further corroborating the distinction of the new taxon. Creptotrema cambeve n. sp. is the 18th nominal Creptotrema species known from South America and the 22nd erected in the genus. This is the first study reporting a trematode in Cambeva spp. hosts and the second parasitological survey carried out for Ca. davisi , a poorly known small endemic fish.

Phylogenetic studies of aberrant species are of considerable scientific interest because their taxonomic rank in traditional systems based on morphological characters is not infrequently overestimated. Apopharynx bolodes (Braun, ) is one of the few psilostomid digeneans devoid of the pharynx. This is considered a sufficient basis for assigning it and similar species to the subfamily Apopharynginae. We found A. bolodes in Fulica atra Linnaeus, 1758 from Belarus, described it morphologically, and genotyped it by the 28S rRNA gene and the ITS2 region. It is the first molecular data on A. bolodes and the first record of this digenean species in Belarus. The phylogenetic analysis based on partial sequences of the 28S rRNA gene showed that A. bolodes is closely related to the Sphaeridiotrema spp. (Sphaeridiotrematinae). However, this phylogenetic inference has not received yet support with data on the ITS2 region.

Despite a great effort made for almost 90 years, the diversity of freshwater fish trematodes in Mexico is still far from being fully known. The addition of molecular data to the description of trematode diversity in the last two decades added the potential to establish more robust species limits and a more accurate biodiversity estimation, but also led in some instances to the recognition of cryptic species complexes. Here, we used sequences of the large subunit of the nuclear ribosomal gene (28S rRNA) as barcodes, and morphological data, to assess the diversity of freshwater fish trematodes from a lake within a tropical rainforest. Eighty freshwater fish specimens of eight species were studied, and 120 trematode specimens were collected. Morphologically, specimens were allocated into nine genera; molecular phylogenetic analyses along with sequence divergence data provided evidence for recognising 11 trematode taxa, six adults and five metacercariae; six of them were identified to species level. Geographical distribution and host association patterns are briefly discussed for each trematode taxa.

The present study aims to describe a new genus and species of microphalloid digenean parasite of two species of bats of the genus Peropteryx from the Mexican Neotropics (in the states of Chiapas and Yucatán). Morphological and molecular data (28s rDNA ribosomal gene sequences) were used to study Digeneans. Sagittatrema zutzi gen. nov. sp., nov., is diagnosed morphologically by having a sagittiform body, a genital pore in the midline of the body, posterior to the ventral sucker, and a cirrus sac running through much of the diameter of the ventral sucker. The nine sequences generated from the 28S rDNA gene were used to examine the phylogenetic affinities of this new taxon within the superfamily Microphalloidea Ward, 1901, using Maximum Likelihood and Bayesian Inference analyses. Both analyses resulted in trees with similar topologies and formed a well-supported clade (Bt = 100; pp = 1) with the Sagittatrema sequences. Because of the new genus's phylogenetic position and that some sister families to the proposed taxa, like Pleurogenidae and Prosthogonimidae, are polyphyletic, we prefer to consider Sagittatrema as a genus incertae sedis within Microphalloidea. A full systematic review of microphalloids is needed to confirm their phylogenetic position.

Species-level delineation of digenetic trematodes is complex and can be best achieved by integrative taxonomy using both genetic characterisation and morphological analysis. Two new Bucephalidae species of the genus Rhipidocotyle Diesing, 1858 are described here based on specimens collected from the intestine of Sphyraena putnamae Jordan & Seale following this approach. Adults of R. siphonyaka n. sp. and R. nolwe n. sp. possess tentacles and a tegument with scales. They are distinguished from their congeners by the arrangement of the digestive structures, the extent of the uterus relative to vitelline fields, and the arrangement of the reproductive structures. Rhipidocotyle siphonyaka n. sp. differs from R. nolwe n. sp. in having the pharynx and mouth positioned in the pre-uterine field, tandem testes, longer body length, and shorter pre-vitelline and post-testicular distance. Rhipidocotyle siphonyaka n. sp. differs from its congeners in having a tube-like intestinal caecum, pharynx and mouth opening positioned in the pre-vitelline field. Rhipidocotyle nolwe n. sp. appears to be similar, morphologically and morphometrically, to Rhipidocotyle khalili (Nagaty, 1937). Despite their similarities, R. nolwe n. sp. has a shorter body length and egg size. Moreover, the molecular analysis of 28S and ITS rDNA fragments indicate that R. siphonyaka n. sp. and R. nolwe n. sp. are closely related phylogenetically but distinct from one another and other Bucephalidae for which molecular data are available.

Members of the genus Maritrema Nicoll, 1907 include endoparasites of aquatic birds and mammals, distributed worldwide. Adult specimens were collected from the intestines of three bird species (the great black hawks, Buteogallus urubitinga Gmelin; laughing gull, Leucophaeus atricilla Linnaeus; and the willet, Tringa semipalmata Gmelin) in three localities along the Gulf of Mexico. Photogenophores were sequenced for the large subunit (LSU) from nuclear rDNA, and the new sequences were aligned with other microphalloid sequences available in GenBank. The maximum likelihood and Bayesian inference analyses revealed three independent lineages, one corresponding to a previously described species, Maritrema corai Hernández-Orts, Pinacho-Pinacho, García-Varela & Kostadinova, 2016, and two representing two undescribed species. These two new species are described in the current study. Maritrema itzamnai n. sp. can be morphologically differentiated from its four congeneric species occurring in coastal areas of Mexico by having smaller oral (20-29 × 20-38 μm) and ventral (20-39 × 19-33 μm) suckers. In addition, Maritrema itzamnai n. sp. possess annular vitellarium instead of a horseshoe-shaped vitellarium. Maritrema kukulkanni n. sp. can be distinguished from its congeneric species reported from Mexico by possessing a larger oesophagus (44-117μm) and by having a vitellarium distributed in both the hindbody and forebody. Maritrema corai is the third species recorded in this study parasitizing the great black hawk ( Buteogallus urubitinga ); this represents a new host and locality record, expanding its distribution range from the Mexican Pacific Ocean to the Gulf of Mexico.

This study focuses on the opecoelid genus Podocotyle, particularly the species in the northern European seas (White, Barents and Pechora), with additional data from few isolates from the Far East. The research combines molecular analyses (28S, 5.8S+ITS2 rDNA, and cox1 mtDNA) and morphological examinations. Molecular analyses suggested that there are most likely four species of Podocotyle in the northern European seas and three more in the Far East. Morphological redescriptions are provided for three northern European species: P. atomon, P. reflexa, and P. odhneri, with the latter recognized as a valid species. The study also verified the life cycle of P. atomon and identified Lacuna vincta (Littorinidae) as the first intermediate host for P. reflexa. In the Sea of Okhotsk, L. turrita is the first intermediate host for two apparently undescribed Podocotyle species. The results also highlight the morphological variability of P. atomon, emphasizing the need for an integrative approach in the taxonomy and biodiversity studies., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Two new species of the genus Allocreadium were isolated from the intestines of the Lake minnow Rhynchocypris percnura caught in the backwater of the Komissarovka River in the South of the Russian Far East. The morphology of A. anastasii n. sp. corresponds to that of Allocreadium sp. from Lake Khar (Mongolia) and Allocreadium sp. Belous, 1952 from the Primorsky region of Russia except for the preacetabular anterior border of the vitelline follicles in A. anastasii n. sp. from the Komissarovka River vs. at anterior half of ventral sucker in Allocreadium sp. Genetic analysis revealed the identity of A. anastasii n. sp. to Allocreadium sp. 1 from the Nezhinka River and Lake Khar. Allocreadium macrolecithum n. sp. was differentiated from Palaearctic Allocreadium spp. by having the following features: respectively large vitelline follicles extending from posterior extremity to anterior margin of the ventral sucker; relatively short caeca reaching the border of middle and posterior thirds of hindbody; and small testes in the middle of hindbody. Interspecific genetic p-distances between Allocreadium spp. were 0.16-7.23% in 28S gene and 18.62-31.54% in Cox1 mtDNA gene. In the phylogenetic tree reconstructed with Maximum parsimony and Bayesian Inference methods, A. anastasii n. sp. and A. macrolecithum n. sp. were nested into different species groups of the genus Allocreadium - sister to A. khankaiense and A. bursense , respectively. Modified dichotomous keys were prepared for 31 Palaearctic species of Allocreadium including A. crassum , A. dogieli , A. papilligerum , A. bursense , A. anastasii n. sp., and A. macrolecithum n. sp.

In light of the morphological and molecular data for cyclocoelids observed from the air sacs of Mareca strepera (Linnaeus) (Anatidae, Anseriformes) caught in the southern region of the Russian Far East, we suggest new insights into the systematics of the family Cyclocoelidae. A comparative morphological and phylogenetic analyzes revealed that new cyclocoelids represented the new genus and species Paracyclocoelum lobatum. Based on the 28S rRNA gene fragment we showed the significant genetic divergence of P. lobatum from the type species of the type genus for the family, Cyclocoelum mutabile (Zeder, 1800) Brandes, 1892 and along with the confusing morphological similarity by the prepharyngeal position of the genital pore it most likely indicate homologous development of the reproductive system of Paracyclocoelum and Cyclocoelum. Here, we provide a new dichotomous key for five cyclocoelid genera from the subfamily Cyclocoelinae including Paracyclocoelum n. g. The new genus Paracyclocoelum had sister relationship to the cyclocoelin genus Circumvitellatrema. Based on the polyphyletic interrelationships of Cyclocoelum and Circumvitellatrema the Cyclocoelinae were assigned with the status sensu lato., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The trematode family Cyathocotylidae infects various hosts worldwide, including birds, mammals, reptiles, and fish. However, the lack of molecular data from adult worms hinders phylogenetic, epidemiological, and host association studies. This study aims to identify the common cyathocotylid trematodes infecting African catfish in Egypt using morphological and molecular evidence. Out of 142 Clarias gariepinus, 123 fish (86.6%) harbored cyathocotylid metacercariae, with a mean metacercarial intensity of 201 ± 38.5/g. Cyathocotylid metacercariae prevalence gradually rose as host size increased. Although there was no significant difference between groups, larger fish had a higher mean metacercarial intensity. The prevalence and intensity were unrelated to the fish gender. Histopathological examination of metacercariae-infected catfish revealed varying degrees of degenerative changes, including intermuscular edema leading to muscle fiber dispersion and atrophy, involving 11% to over 81% of muscle sections. We identified three cyathocotylid metacercariae and eight cyathocotylid adult species from experimental infection using morphometric and molecular data, including internal transcribed spacer (ITS) and/or mitochondrial cytochrome c oxidase subunit 1 (cox1) sequences. We determined the phylogenetic position of these cyathocotylid samples. The ITS sequence analysis linked the isolated Cyathocotylidae sp. 1 and 2 metacercariae to Prohemistomum vivax adults. Mesostephanus appendiculatoides and Paracoenogonimus ovatus were reported for the first time in Egypt. These findings may provide valuable genetic data for future molecular epidemiological and phylogenetic studies of cyathocotylid trematodes., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Encotyllabe percussa n. sp. is proposed based on morphology and DNA sequences analysis of ribosomal (18S, 28S) and mitochondrial (COI) gene fragments. Encotyllabe percussa n. sp. was found infecting the spangled emperor Lethrinus nebulosus (n = 75) with higher prevalence from Dibba, Musandam (Gulf of Oman) than in Dhofar Salalah (Indian Ocean), Oman (p = 0.03). The general morphology of E. percussa n. sp. resembles E. caballeroi, E. chironemi and E. spari, which exhibit pre-equatorial testes. However, E. percussa n. sp. shows unique morphological characteristics distinguishing from congeneric species: the large hamuli bear notch allocated externally between the first half proximal of the root, and the small hamuli exhibit semicircular shape with undivided roots. Phylogenetic relationships within the Encotyllabe genus remain unresolved. However, the tree topology with the 28S showed overall consistency with the principal component analysis arrangement (PCA) derived from the morphological analysis. Which showed that the large and small hamuli, marginal hooks, ovary, testes (length and width) and peduncle are currently the most important morphological traits within the genus. Cytochrome c oxidase subunit I (COI) gene fragment showed high interspecific genetic divergence adding unambiguous resolution to discriminate/designate species identity. Interrelations within the genus support the identity of Encotyllabe percussa as a new species. This is the first species characterized with three gene fragments, the second congeneric species described in L. nebulosus and the first recorded in Oman., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Rhopalocercous Cercaria duplicata von Baer, 1827 develops in an intermediate host, the unionid bivalve Anodonta anatina (L.), but its adult form has been unknown. We examined eight fish species occurring in the presence of a highly infested population of A. anatina in the Zesławice reservoir (S Poland). Gravid Phyllodistomum specimens were obtained from the ureters of ide, Leuciscus idus (L.) and common rudd, Scardinius erythrophthalmus (L.). One of the rudd specimens was doubly infected, a trematode was also found in the urinary bladder. In addition, a gravid Phyllodistomum specimen was found in the ureter of a tench Tinca tinca (L.), caught in Lake Ilmėdas (Lithuania). In order to clarify the phylogenetic position of larval and adult gorgoderids and to establish their life cycle, ITS2 and 28S rDNA sequences were analysed. The analysis showed that adult Phyllodistomum specimens located in the ureters are conspecific with C. duplicata. The trematode found in the urinary bladder of S. erythrophthalmus was P. folium (Olfers, 1816). It is suggested that adult stages of C. duplicata should be referred to as Phyllodistomum duplicatum n. comb. The intercaecal position of the uterus and the deeply-lobed ovary are the main features distinguishing it from other Phyllodistomum species. Host specificity and ecology are discussed., (© 2024. The Author(s).)

The type species of the genus Halipegus Looss, 1899, Halipegus ovocaudatus (Vulpian, 1859) is a generalist parasite of different species of amphibians, mainly anurans. To date, the phylogenetic position of this species has not been established. Specimens of H. ovocaudatus, were collected from three species of water frogs, Pelophylax ridibundus (Pallas), P. esculentus (Linnaeus), and P. lessonae (Camerano) inhabiting the Middle Volga region (European Russia). In our study, we provide detailed morphological redescription of these digeneans and combine it with molecular phylogenetic analyses based on partial sequences of the 28S rDNA and coI mtDNA genes. The phylogenetic position of H. ovocaudatus among the derogenids has been established as a sister clade to other representatives of the Halipeginae. We compared pairwise distances based on partial sequences of coI mtDNA genes of H. ovocaudatus and other representatives of Derogenidae. It was shown, that adults of H. ovocaudatus from different hosts are representatives of the same species. Specimens parasitizing three frog hosts from several localities differ slightly in body shape and size, which probably reflects host-induced intraspecific variability., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

We examined several American alligators, Alligator mississippiensis (Daudin, 1802) (Crocodilia: Alligatoridae) from Louisiana, Alabama, and South Carolina in August 2022. The intestine of one alligator from Alabama was infected by Dracovermis occidentalis Brooks and Overstreet, 1978 (Platyhelminthes: Digenea: Liolopidae Odhner, 1912), a seldom collected and incompletely described trematode that lacks a representative nucleotide sequence. Liolopidae comprises 5 genera and 15 species: Liolope spp. infect giant salamanders; Helicotrema spp. infect turtles and lizards; Harmotrema spp. infect snakes; Paraharmotrema spp. infect turtles; and Dracovermis spp. infect crocodilians. Based on our study of the newly collected specimens and the holotype of D. occidentalis, we redescribe D. occidentalis, correct errors in its original description, and provide an updated phylogeny for Liolopidae that, for the first time, includes Dracovermis Brooks and Overstreet, 1978. Our specimens were identified as D. occidentalis by having testes in the posterior 1/3 of the body, a pretesticular cirrus sac, a spined and eversible cirrus, a bipartite seminal vesicle, and a post-acetabular vitellarium. A phylogenetic analysis of the D1-D3 domains of the nuclear large subunit ribosomal DNA (28S) recovered Liolopidae as monophyletic; however, low taxon sampling in the group precludes hypothesis-testing about liolopid-vertebrate cophyly. This is the first collection for morphological study of the type species for Dracovermis since the genus was proposed 46 years ago, the first record of a liolopid from Alabama, and the first phylogenetic analysis that includes Dracovermis., (© 2024. The Author(s).)

Parasites belonging to the trematode family Clinostomidae have a global distribution. Freshwater fish in Bangladesh frequently serve as hosts for different clinostomid species. During the metacercaria stage, the digenetic trematode Euclinostomum heterostomum exhibits a specific preference for Channidae species, where it undergoes encystment within the liver, kidneys, and muscles of these hosts. The study aimed to identify E. heterostomum in Channa punctata through combined morphological and molecular analysis. Light and scanning electron microscopy were conducted to investigate the morphological characteristics of the species. The histological examination of the infected liver tissue revealed the presence of encysted flukes, inflammatory leukocyte infiltrates, and degeneration and loosening of hepatic tissue. In molecular analysis, the generated internal transcribed spacer 1 (ITS1), 5.8S ribosomal DNA and ITS2 regions sequence (GenBank accession no: OR591452) of 830 bp showed 100% identity with Euclinostomum heterostomum identified in India (MT785786). The phylogenetic reconstruction provided substantial evidence of genetic similarities (0-1% genetic distance) among different isolates of the genus Euclinostomum, suggesting that there is a shared heritage., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

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.

Octomacrum spinum Dansby & Shoemaker, 1973, is reported for the first time from 23 of 146 (16%) highland stonerollers, Campostoma spadiceum collected from central and western Arkansas and southeastern Oklahoma, USA. Analysis of molecular data revealed that the SSU rRNA gene of specimens of O. spinum from Arkansas was identical to a number of Octomacrum spp. and the LSU rRNA gene was 97.46% similar to Octomacrum europaeum. We also provide a summary of the species of Octomacrum reported from North American and European fishes., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Background: The Bucephalidae is a large family of digenean trematodes but most previous analyses of its phylogenetic position have relied on a single mitochondrial gene or morphological features. Mitochondrial genomes (mitogenomes) remain unavailable for the entire family. To address this, we sequenced the complete mitogenome of Dollfustrema vaneyi and analyzed the phylogenetic relationships with other trematodes., Results: The circular genome of Dollfustrema vaneyi spanned 14,959 bp and contained 12 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and a major non-coding region. We used concatenated amino acid and nucleotide sequences of all 36 genes for phylogenetic analyses, conducted using MrBayes, IQ-TREE and PhyloBayes. We identified pronounced topological instability across different analyses. The addition of recently sequenced two mitogenomes for the Aspidogastrea subclass along with the use of a site-heterogeneous model stabilized the topology, particularly the positions of Azygiidae and Bucephalidae. The stabilized results indicated that Azygiidae was the closest lineage to Bucephalidae in the available dataset, and together, they clustered at the base of the Plagiorchiida., Conclusions: Our study provides the first comprehensive description and annotation of the mitochondrial genome for the Bucephalidae family. The results indicate a close phylogenetic relationship between Azygiidae and Bucephalidae, and reveal their basal placement within the order Plagiorchiida. Furthermore, the inclusion of Aspidogastrea mitogenomes and the site-heterogeneous model significantly improved the topological stability. These data will provide key molecular resources for future taxonomic and phylogenetic studies of the family Bucephalidae., (© 2024. The Author(s).)

The Manila clam Ruditapes philippinarum on the west coast of Korea harbors several digenetic trematodes. However, most studies in this region have been restricted to a few sampling sites and the current species designation of some trematodes is largely based on morphology, leaving the molecular phylogenetic position among the Digenea unsolved. Thus, we first provide both morphology and molecular phylogeny of some components in the trematodes community in the Manila clam based on a large-scale survey of 26 sites on the west coast, where well-developed tidal flats serve as large commercial clam culture beds. Our study revealed that the trematodes community in the clams consisted of at least 5 species that belong to 3 families (Himasthlidae, Gymnophallidae, Baccigeridae) and 1 superfamily (Monorchioidea). The life mode of the 5 different species included the metacercaria and sporocyst, with one species (Parvatrema duboisi) utilizing the clams as both the first and/or second intermediate host. Trematode infection prevalences were not evenly distributed among the study sites, although the reasons behind this are yet to be determined. Morphological identification was confirmed with the molecular analyses based on ITS and 28S rDNA; phylogenetic analysis also revealed that Cercaria pectinata infecting the clam gonad should be referred to as Bacciger bacciger hereafter. The present preliminary study provides a crucial baseline that could be further developed in a future study on the digenean trematodes community in the Manila clam., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Objectives: An integrative taxonomic description of Aponurus laguncula (Lecithasteridae), a digenean parasitic species of Chaetodipterus faber (Acanthuriformes) from Brazilian Southeast, is provided. Morphological techniques, as whole mounted slides, histology and scanning electron microscopy, and molecular analyses supported that integrative description., Methods: Fifteen digenean specimens were stained in hydrochloric carmine and mounted on permanent slides. Two specimens were stained in hematoxylin and eosin following histological routine processing. Four parasites were dehydrated through a graded ethanol series, critical point dried with carbon dioxide and coated with gold to scanning electron microscopy analysis. Sequence of the large ribosomal subunit (28S rDNA) gene was generated and used to construct a phylogeny based on maximum likelihood and Bayesian inference analyses., Results: Morphological description and morphometric data obtained in present study were in accordance with previous studies of the species. Use of another morphological techniques, as scanning electron microscopy and histology, corroborated the observed features of whole mounted slides. Also, they provided a better observation of previous reported characteristics and new features reporting, such as an elongated hermaphroditic duct, a smooth tegument and cells that compose the prostatic gland. The molecular sequence obtained in the present study formed a robust clade with available sequences of species of Aponurus., Conclusions: The integrative taxonomic approach successfully combined morphological observations, including both previously reported features and new descriptions from histological and electron microscopy analyses, with molecular data to identify these specimens as A. laguncula. Moreover, the detailed characterization of structures, such as the gonads in A. laguncula, that would be challenging to analyze using a single technique, was possible. Further molecular studies with less conserved genetic markers should be conducted to understand phylogenetic relationships between Aponurus species., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Monogeneans of the genus Dactylogyrus Diesing, 1850, the largest genus in the family Dactylogyridae, mostly parasitize the gills of cyprinoid hosts; however, only 3 Dactylogyrus' mitochondrial genomes (mitogenomes) are studied so far. The aim of this research is to extend our understanding of the mitogenomes of Dactylogyrus. We sequenced the mitogenomes of D. crucifer and D. zandti isolated from Rutilus rutilus and Abramis brama orientalis in northwest China, and then we compared these mitogenomes with other monogeneans. We used Illumina NovaSeq to sequence the entire mitochondrial genomes of D. crucifer and D. zandti and characterized the mitogenomes to understand the gene structure, gene identity, the secondary structures of the 22 tRNA genes, and relative synonymous codon usage. We used the analytic Bayesian Information and Maximum Likelihood methods to determine their associated phylogenetic trees. The mitogenomes of D. crucifer and D. zandti were 14,403 and 18,584 bp, respectively. Organization and positioning of these genes were in accordance with Dactylogyrus lamellatus and Dactylogyrus tuba. The nucleotide composition of Dactylogyridae was different from other families of Monogenea, and the A+T count of genus Dactylogyrus (54 - 58.4 %) was lower than other genus species of the family Dactylogyridea (63.9 - 78.4 %) in protein-coding genes. Dactylogyrus members displayed a codon usage bias. The relative synonymous codon used by Dactylogyrus was not conserved and was lower than other monogeneans. The codon use patterns of closely-related species isolated from closely-related hosts were identical. Phylogenetic analyses using mitogenomic dataset produced Dactylogyrus isolated from host subfamily Leuciscinae formed a sister-group. Our results contributed significantly to an increased database of mitogenomes, more than 50 %, for Dactylogyrus that may help future studies of mitochondrial genes and codon uses for the analysis of monogenean phylogenetics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The Cyathocotylidae Mühling, 1896 is a small but broadly distributed family of digeneans parasitic in a wide range of vertebrate definitive hosts, from fish to mammals. Despite existing taxonomic questions, only a few studies have generated DNA sequence data from cyathocotylids, and only a single publication included sequence data from a cyathocotylid parasitic in snakes. Four genera are known to infect snakes: GogateaLutz, 1935, Szidatia Dubois, 1938, MesostephanoidesDubois, 1951, and SerpentostephanusSudarikov, 1961. Members of these genera were known from only Asia and Africa. In the present study, we describe 2 new species of Gogatea from snakes in Australia and 1 from Vietnam. The new species from Vietnam described herein is the first member of the genus that lacks a ventral sucker. We used partial sequences of the nuclear large ribosomal subunit (28S) and mitochondrial cytochrome c oxidase subunit I (COI) genes to explore phylogenetic relationships among cyathocotylids and species differentiation. In addition, this is the first report of a cyathocotylid from snakes in Australia, thus posing interesting questions regarding the dispersal and historical biogeography of these parasites. Cyathocotylid genera from snakes have a long, convoluted taxonomic history. The genera Gogatea, Mesostephanoides, and Szidatia were distinguished from each other based on very small morphological differences. Therefore, the validity of Szidatia and Mesostephanoides was often questioned in the literature. Based on the detailed morphological analysis of our freshly collected high-quality specimens and comparison with published information, we synonymize Mesostephanoides and Szidatia with Gogatea., (© American Society of Parasitologists 2024.)

A new species of hemiurid trematode found on the gills and in the aorta of the pelagic thresher Alopias pelagicus from the eastern Pacific, off Costa Rica, is described based on an integrative taxonomic approach that includes the use of light and scanning electron microscopy, and 28S rDNA sequencing. Phylogenetic analysis was also performed to explore, for the first time, the relationships of a member of the subfamily Otiotrematinae within the suborder Hemiurata. Paronatrema davidbowiei n. sp. can be distinguished from the congeners by having tegumental spines on the dorsal surface of the forebody, papillae on the oral sucker, and different morphology or number of testicular follicles. BLAST analysis revealed that sequences of Paronatrema davidbowiei n. sp. had the highest degree of similarity with Hirudinella spp. (Hirudinellidae). Results from Maximum Likelihood and Bayesian phylogenetic analyses, returning trees with the exact same topology and strong branch support, distinguished between the two superfamilies included in the suborder Hemiurata: Azygioidea and Hemiuroidea. Our analysis placed the new species in a clade with Copiatestes filiferus, the only existing sequence of the family Syncoeliidae., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2024. Published by Elsevier B.V.)

Echinochasmids are a group of globally distributed digeneans, and the adults are found in the intestines of birds, mammals and reptiles. In the Neotropical region of Mexico, adult specimens were obtained from seven fish-eating bird species in six localities, whereas specimens of Stephanoprora aylacostoma were obtained experimentally in Argentina. Morphologically, the new specimens from the Neotropical region of Mexico were identified as Stephanoprora uruguayense and an undescribed species of Echinochasmus. Sequences for two nuclear (large subunit (28S) and internal transcribed spacer from DNA ribosomal (ITS1-5.8S-ITS2)) molecular markers were generated and analysed together with other sequences downloaded from GenBank. The phylogenies obtained with each molecular marker indicated that Echinochasmus is paraphyletic and agreed with previous phylogenetic studies. The first cluster included the type species (E. coaxatus, which has 24 head-collar spines) plus three congeneric species. The second cluster contained species of Echinochasmus plus Stephanoprora, including the species analysed herein, S. uruguayense, S. aylacostoma (with 22 head-collar spines) and Echinochasmus sp. (with 20 head-collar spines), which formed three independent subclades, allowing us to recognize a lineage that was described morphologically as a new species. Echinochasmus ostrowskiae n. sp. can be distinguished from its congeners by having a head collar with 20 spines in a single row, seven spines on each edge and three angle spines, and a pharynx with an irregular edge and by the body, egg and collar spine sizes. Additionally, new host and locality records for S. uruguayense are presented, expanding its geographical distribution range in the Americas., 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.)

Three new species of Gyrodactylus are described from three species of bitterling in Donghu Lake, China: Gyrodactylus ocellorhodei n. sp. from Rhodeus ocellatus; G. sinenorhodei n. sp. from Rhodeus sinensis; and G. acheilorhodei n. sp. from Acheilognathus macropterus. All the three new species showed similar opisthaptor morphology, especially the marginal hooks: all had a slender and perpendicular sickle shaft, and flat sickle base with distinct heel and inner arch which was different from the G. rhodei-group species parasitic on bitterling. Multivariate analyses based on hamulus and marginal hooks suggested that these three new species cannot be completely distinguished, despite some morphology divergence observed in certain less reliable morphometric features, such as hamulus root length, ventral bar total length and process shape. These three new species shared an identical 18S ribosomal RNA gene sequence, while the variation in the Internal Transcribed Spacers (ITS1-ITS2) sequence among them (8.4-11.2%, K2P) far exceeded the 1% ITS sequence difference that had been suggested as a threshold for species delimitation of Gyrodactylus. Phylogenetic analysis based on ITS1-ITS2 showed that all these sequenced Gyrodactylus spp. parasitic on the subfamily Acheilognathinae host formed a monophyletic group. However, a clear differentiation (18.9-20.9%, K2P of ITS1-ITS2) could be found between the subgroup from China (G. ocellorhodei n. sp., G. sinenorhodei n. sp. and G. acheilorhodei n. sp.) and that from Europe (G. rhodei)., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Haliotrema Pteroisi: Paperna, 1972 (Monogenoidea: Dactylogyridae) was found parasitizing the gill lamellae of devil firefish, Pterois miles (Bennet) (Perciformes: Scorpaenidae), in the Red Sea off Safaga (26°44'N, 33°56'E), Egypt. The parasite species was described based on morphological features of available specimens and transferred to PlatycephalotremaKritsky and Nitta, 2019 (Dactylogyridae) as Platycephalotrema pteroisi (Paperna, 1972) n. comb. The occurrence of Pl. pteroisi off Safaga, Egypt, represented a range extension for the helminth of about 160 km to the southwest of the southern end of the Gulf of Aqaba. The transfer of the species to Platycephalotrema based on an evaluation of morphological features was supported by an analysis of molecular sequences of the 28S rDNA gene of Pl. pteroisi and 49 other dactylogyrid species. Maximum-likelihood, Bayesian inference, and maximum parsimony analyses of this dactylogyrid sequence data revealed H. pteroisi to nest with significant support within the clade of Platycephalotrema spp. During the literature review of dactylogyrid species infecting scorpionfishes, it was determined that Ancyrocephalus sp. of Dyer et al. from luna lion fish Pterois lunulata Temminck and Schlegel collected off Okinawa-jima, Japan represented an undescribed species of Platycephalotrema., (© American Society of Parasitologists 2024.)

Members of the genus Scaphanocephalus mature in accipitrids, particularly osprey, Pandion haliaetus , with metacercaria causing Black Spot Syndrome in reef fishes. In most of the world, only the type species, Scaphanocephalus expansus (Creplin, 1842) has been reported. Recent molecular studies in the Western Atlantic, Mediterranean and Persian Gulf reveal multiple species of Scaphanocephalus , but have relied on 28S rDNA, mainly from metacercariae, which limits both morphological identification and resolution of closely related species. Here we combine nuclear rDNA with mitochondrial sequences from adult worms collected in osprey across North America and the Caribbean to describe species and elucidate life cycles in Scaphanocephalus . A new species described herein can be distinguished from S. expansus based on overall body shape and size. Phylogenetic analysis of the whole mitochondrial genome of Scaphanocephalus indicates a close relationship with Cryptocotyle . We conclude that at least 3 species of Scaphanocephalus are present in the Americas and 2 others are in the Old World. Specimens in the Americas have similar or identical 28S to those in the Mediterranean and Persian Gulf, but amphi-Atlantic species are unlikely in light of divergence in cytochrome c oxidase I and the lack of amphi-Atlantic avian and fish hosts. Our results provide insight into the geographic distribution and taxonomy of a little-studied trematode recently linked to an emerging pathology in ecologically important reef fishes.

The Cyathocotylidae Mühling, 1898 is a family of primitive diplostomoid trematodes important for understanding the evolution of the superfamily Diplostomoidea. However, cyathocotylids remain poorly studied with the use of molecular techniques. In this study we sequenced the 5.8S + ITS2 region, 28S rRNA , and cox1 genes of two cyathocotylid species and obtained new morphological data on them. We propose Georduboisia nom. nov. instead of the preoccupied name Duboisia Szidat, 1936 (junior homonym of Duboisia Stremme, 1911). Adults of Georduboisia cf. teganuma (Ishii, 1935) and Paracoenogonimus ovatus Katsurada, 1914 were collected from fish-eating birds in the south of the European part of Russia. Georduboisia cf. teganuma was very similar to G. teganuma gene dataset provided the best-resolved phylogeny of the Cyathocotylidae to date. In the phylogram based on partial sequences of this gene, 28S rRNA gene dataset provided the best-resolved phylogeny of the Cyathocotylidae to date. In the phylogram based on partial sequences of this gene, P. ovatus was close to members of Holostephanoides Dubois, 1983, Neogogatea Chandler & Rausch, 1947 and Gogatea Szidat, 1936. Georduboisia cf. teganuma clustered with members of Cyathocotyle Mühling, 1896 and Holostephanus Szidat, 1936. Phylogenetic analysis based on the 5.8S + ITS2 dataset showed that adults of P. ovatus examined in our study were conspecific with the metacercariae from the musculature of fish collected in Hungary and Italy. It also revealed probable misidentifications of larvae and adults of cyathocotylids whose sequences are deposited in GenBank NCBI.

Ochoterenatrema Caballero, 1943 is a genus of lecithodendriid digeneans that prior to this study included 8 species parasitic in bats in the Western Hemisphere. Species of Ochoterenatrema possess a unique morphological feature in form of the pseudogonotyl on the sinistral side of the ventral sucker. In this study, we describe 2 new species of Ochoterenatrema from bats in Ecuador. The new species are readily differentiated from their congeners by a combination of morphological characters, including the distribution of vitelline follicles, length of oesophagus, sucker ratio and the body shape, among other features. We have generated partial nuclear 28S rDNA and mitochondrial cox1 gene DNA sequences from both new species. The newly obtained sequences were used to differentiate among species and study the phylogenetic interrelationships among Ochoterenatrema spp. The internal topology of the clade was weakly supported, although the cox1 tree was much better resolved than the 28S tree. Comparison of sequences revealed 0-1.2% interspecific divergence in 28S and 3.3-20.5% interspecific divergence in cox1 among Ochoterenatrema spp. The new findings demonstrate that bats in South America likely harbor multiple additional undescribed species of Ochoterenatrema. More extensive sampling from broader geographic and host ranges, especially in North America, should allow for a better understanding of the evolution of host associations and morphological traits of this lineage of lecithodendriid digeneans., (© 2024. The Author(s).)

Clinostomum is a cosmopolitan genus of trematodes that infect piscivorous birds, freshwater molluscs, freshwater fish and amphibians. Herein, a novel species of Clinostomum is described based on morphological and molecular data from an adult in the oral cavity of the great blue heron Ardea herodias and metacercariae collected from the gills and skin of American bullfrog tadpoles Rana catesbeiana. The novel species shares similar qualitative and quantitative morphological features with a congener, Clinostomum marginatum, which has overlap in host and geographic distribution. The most notable morphological difference when compared to C. marginatum is the greater posterior testis length of the novel species. Molecular data resolved similarities with morphological comparisons to nominal species and supports the establishment of a novel species. Molecular data include partial small ribosomal subunit (18S rRNA gene), ribosomal internal transcribed spacer regions (ITS1, 5.8S rRNA gene, and ITS2), partial large ribosomal subunit (28S rRNA gene), cytochrome c oxidase subunit 1 gene (cox1), and nicotinamide adenine dinucleotide dehydrogenase subunit 1 gene (nad1) sequences. Phylogenetic analyses place the novel species in a sister clade to C. marginatum. Morphological and molecular data, combined with phylogenetic analyses support the establishment of Clinostomum dolichorchum n. sp., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The deepest recorded depth for trematodes currently stands at approximately 6200 m. This depth record was achieved solely through sequence datasets of Lepidapedon sp. obtained from a gastropod. Given that trematodes of this genus typically use fish as definitive hosts, the origin of the trematode sequence was thought to be larval stages. However, the specific species remained unclear owing to the absence of reported adult-stage sequences. In the present study, we definitively identified the deepest trematode as Lepidapedon oregonense by comparing 28S ribosomal DNA sequences from adult worms from the macrourid fish Coelorinchus gilberti with data from the gastropod in the previous study.

The genus Ancyrocephalus sensu lato is a large assemblage of species of dactylogyrid monopisthocotyleans without clear taxonomic boundaries. Despite an urgent need for revision, only three representatives of this taxon have been molecularly characterised so far. We found specimens of Ancyrocephalus curtus , a previously non-genotyped species, in gills of Perccottus glenii caught in the River Syumnyur, Amur Basin, Russia. The aim of this study was to assess the phylogenetic position of this parasite using partial sequences of 28S rRNA gene. In the phylogenetic tree, A. curtus appeared as a sister taxon to the dactylogyrine genus Gobioecetes. The new molecular evidence supports the hypothesis about the non-monophyletic status of Ancyrocephalus sensu lato.

Presenting new molecular and scanning electron microscope (SEM) features, this study gives additional data to the better knowledge of Thaparocleidus vistulensis (Siwak, 1932) (Monopisthocotyla, Ancylodiscoididae), a parasite of the European catfish Silurus glanis Linnaeus, 1758 (Siluriformes, Siluridae) cultured in a commercial fish farm in Hungary. In addition, notes on the early development of sclerotized anchors are also provided. The main morphological difference of T. vistulensis compared to other congeneric species is associated with the male copulatory organ, which exhibits 5-7 loops in the middle of the penis length and a long open V-shaped sclerotized accessory piece, dividing terminally into two parts, securing the terminal part of the penis tube. The present study provides for the first time molecular characterization data based on the 2694 bp long nucleotide sequence of rDNA (ITS1, 5.8S, ITS2, and flanked with partial 18S and partial 28S) submitted in GenBank with the accession number OR916383. A phylogenetic tree based on ITS1 sequences supports a well-defined clade including T. vistulensis, forming a sister group with T. siluri, a species-specific monopisthocotylan parasite to S. glanis. The morphological characterization of T. vistulensis, especially for the male copulatory organ, together with the molecular data in the present study, extends knowledge about this monopisthocotylan species and provides new information for future phylogeny studies., (© 2024. The Author(s).)

Two new species of Urocleidoides are described from the gills of Pseudanos trimaculatus (Characiformes: Anostomidae) from the coastal drainages of the Eastern Amazon, Brazil. Urocleidoides itabocaensis n. sp. is characterized by having a sclerotized, tubular, sigmoid male copulatory organ (MCO), a circular sclerotized tandem brim associated with the base of the MCO; an accessory piece articulated with the MCO, a V-shaped, divided into two subunits, distal subunit spoon-shaped; and a vaginal pore dextroventral with opening marginal. Urocleidoides omphalocleithrum n. sp. is characterized by presenting a C-shaped or sigmoid MCO; an accessory piece articulated with the MCO, L-shaped, divided into two subunits, distal subunit gutter-shaped; a vaginal pore dextroventral with opening marginal; and a ventral bar broadly V-shaped, with anteromedial projection. Molecular phylogenetic analysis based on partial 28S rDNA and COI mtDNA genes indicate that U. itabocaensis n. sp. and U. omphalocleithrum n. sp. are closely related and appear as a sister group to other Urocleidoides species (U. paradoxus, U. digitabulum and U. sinus) parasitizing anostomid fishes. This study represents the first record of monogenoids from the gills of P. trimaculatus for the Eastern Amazon., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Invasive snails are associated with ecological problems in freshwater bodies worldwide. However, their impact on the transmission of digenean infections remain underreported. In the present study, 1708 specimens representing four snail species were sampled from four impoundments in the Limpopo River system in South Africa. Gyraulus chinensis (Planorbidae), Physella acuta (Physidae) and Pseudosuccinea columella (Lymnaeidae), which are invasive, were found in all the sampling sites. In contrast, the native lymnaeid Radix natalensis occurred at only one study site. Digeneans were observed only from R. natalensis (prevalence = 49%) and Ps. columella (prevalence = 23%). Morphological and genetic analyses revealed four digeneans: Fasciola nyanzae, Orientocreadium sp., Petasiger sp. and Patagifer vioscai. Pseudosuccinea columella was infected by the four digeneans while R. natalensis harboured only Orientocreadium sp. and Petasiger sp. Partial sequences of Orientocreadium sp. from the current study differed from congeners whose DNA data are available on GenBank, by p-distances of at least 1.84 and 2.2% for 28S and the internal transcribed spacer (ITS) rDNA, respectively. Phylogenetic analyses demonstrated that the present species is sister to Orientocreadium batrachoides. Genetic and phylogenetic data based on 28S and ITS rDNA suggested that Petasiger sp. from the present study and isolates of three unidentified Petasiger spp. from Kenya, Hungary and Australia, were representatives of the same species. This is the first known report of Orientocreadium, Petasiger and Patagifer from Ps. columella. The occurrence of F. nyanzae in Ps. columella indicates spillback from R. natalensis. These findings echo the concerns raised in previous studies about the potential role of Ps. columella in the amplification of digenean diseases in its introduced range. Phylogenetic analyses of partial sequences of the cytochrome c oxidase subunit 1 mitochondrial gene (cox1) showed multiple lineages of Ps. columella in North and South America. Pseudosuccinea columella specimens from the present study belong to an invasive genotype that has spread globally and has been reported from Zimbabwe, Egypt, Portugal, Australia, Argentina, Colombia and New Mexico (USA). Physella acuta from the current study had a stronger genetic relationship with isolates from Canada and Iceland, than with isolates from other parts of Africa, suggesting several invasion routes into Africa. This is the first known DNA characterisation of G. chinensis from Africa. Phylogenetic reconstruction indicated multiple exit events of G. chinensis from Asia into Europe and Africa. South African isolates clustered in a recent branch containing isolates from the Czech Republic and Hong Kong, China. Considering the presence of invasive snails in all the sampling sites in the present study, it is necessary to investigate the factors that enhance their establishment and to monitor their effects on the native snail populations., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

New morphological and molecular data were generated for trematodes recovered from the intestines of the fish Pseudaspius hakonensis from two locations in the south of the Russian Far East. Morphologically, these trematodes are identical to Pseudozoogonoides ugui (Microphalloidea: Zoogonidae) from Japan. According to results of phylogenetic analysis based on 28S rDNA sequence data, P. ugui was closely related to Zoogonoides viviparus , and P. subaequiporus appears as a sister taxon to these two species. Genetic distance values, calculated based on both 28S rDNA and ITS2 rDNA, between P. ugui and Z. viviparus represents an interspecific differentiation level. Our results have an ambiguous explanation, indicating that the implication of the presence of one or two compact vitellarial aggregations for the differentiation of Zoogonoides and Pseudozoogonoides should be reconsidered or that our results open up the question of the taxonomical status of trematodes previously denoted as Z. viviparus and P. subaequiporus.

As part of a parasitological survey, several specimens of two new monopisthocotylean species, Neotetraonchus celsomanueli sp. nov. and N. peruvianus sp. nov. (Dactylogyridea, Dactylogyridae), were collected from the gill filaments of the Peruvian sea catfish Galeichthys peruvianus (Siluriformes, Ariidae) off Puerto Pizarro, Tumbes region, Peru. Neotetraonchus celsomanueli sp. nov. is characterised by an MCO with a T-shaped distal end and an accessory piece that is ribbed and expanded proximally with a worm-shaped termination. Neotetraonchus peruvianus sp. nov. is typified by its MCO, which has a sledgehammer-shaped distal end and an accessory piece with a claw-shaped distal end. Additionally, N. peruvianus sp. nov. is characterised by its jellyfish-shaped onchium. A partial 28S rDNA sequence was obtained from N. celsomanueli sp. nov., and a phylogenetic analysis was conducted. This analysis revealed the phylogenetic position of Neotetraonchus celsomanueli sp. nov. within a clade comprising monopisthocotylean parasites of diadromous and marine ariid catfishes, including Hamatopeduncularia spp., Chauhanellus spp., Thysanotohaptor Kritsky, Shameem, Kumari & Krishnaveni, , and Neocalceostomoides spinivaginalis Lim, 1995. This finding brings the number of known Neotetraonchus species to seven and represents the first described Neotetraonchus species infecting marine catfishes from Peru.

Exploring the phylogenetic signal of morphological traits using geometric morphometry represents a powerful approach to assess the relative weights of convergence and shared evolutionary history in shaping species' forms. We evaluated the phylogenetic signal in shape and size of ventral and dorsal haptoral anchors of 10 species of monogenoids ( Hamatopeduncularia , Chauhanellus and Susanlimocotyle ) occurring in marine catfish (Siluriformes: Ariidae) from the Atlantic coast of South America. The phylogenetic relationships among these species were mapped onto the morphospaces of shape and size of dorsal and ventral anchors. Two different tests (squared change-parsimony and K ) were applied to establish whether the spatial positions in the phylomorphospace were influenced by phylogenetic relationships. A significant phylogenetic signal was found between anchor form and parasite phylogeny. Allometric effects on anchor shape were non-significant. Phylogenetically distant species on the same host differed markedly in anchor morphology, suggesting little influence of host species on anchor form. A significantly higher level of shape variation among ventral anchors was also found, suggesting that the evolutionary forces shaping ventral anchor morphology may operate with differing intensities or exhibit distinct mechanisms compared to their dorsal counterparts. Our results suggest that phylogenetic relationships were a key driver of changes in shape (but not size) of anchors of monogenoids of South American ariids. However, it seems that the emergence of the digitiform haptor in mult ) were applied to establish whether the spatial positions in the phylomorphospace were influenced by phylogenetic relationships. A significant phylogenetic signal was found between anchor form and parasite phylogeny. Allometric effects on anchor shape were non-significant. Phylogenetically distant species on the same host differed markedly in anchor morphology, suggesting little influence of host species on anchor form. A significantly higher level of shape variation among ventral anchors was also found, suggesting that the evolutionary forces shaping ventral anchor morphology may operate with differing intensities or exhibit distinct mechanisms compared to their dorsal counterparts. Our results suggest that phylogenetic relationships were a key driver of changes in shape (but not size) of anchors of monogenoids of South American ariids. However, it seems that the emergence of the digitiform haptor in Hamatopenducularia and in some species of Chauhanellus played an important role in the reduction in anchor size and may cause secondary losses of anchors in other groups of monogenoids.

Objectives: The present work aims to expand the knowledge of the digenean species Prosogonotrema bilabiatum (Sclerodistomidae), a parasite of Chaetodipterus faber (Acanthuriformes) from Brazil, with an integrative taxonomic approach, using light microscopy, scanning electron microscopy, histology, and molecular biology., Methods: Forty-one digenean specimens were stained with hydrochloric carmine for morphological studies. Eleven parasites were dehydrated through a graded ethanol series, critical point dried with carbon dioxide, and coated with gold for scanning electron microscopy analysis. Four specimens were processed following histological routine and stained with hematoxylin and eosin and Gomori trichrome. DNA extracted was amplified using 28S partial primer D1-D3. Maximum likelihood and Bayesian inference were performed for phylogenetic analysis., Results: Morphometric and morphological data of the specimens studied ranged in accordance as observed in previous descriptions of the species. Observations from scanning electron microscopy and histology corroborated with those observed in stained whole mounts. Molecular analysis showed that specimens of P. bilabiatum from Brazil clustered with another two sequences of this species from different hosts and localities, with a high node support value., Conclusions: The integrative taxonomic approach allowed to record and describe new characteristics of P. bilabiatum related to the tegument, the structure and the arrangement of its tissues. The use of molecular markers confirmed that specimens identified as P. bilabiatum from different hosts and localities are all conspecific. Further studies, mainly molecular with less conserved genetic markers, should be carried out to better understand the phylogenetic relationships of Prosogonotrema with Hemiuroidea., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Purpose: Derogenes ruber Lühe, 1900, the type-species of the genus Derogenes Lühe, 1900, is a poorly known derogenid digenean. The original description of this species was not illustrated and aspects of the morphology of the parasite from the type-host remain scarce. Available records of this species were brief and/or lacked illustrations and were based on morphology alone. Additionally, molecular data for Derogenes spp. are warranted to untangle species complexes as they provide a better assessment of interspecific genetic divergence., Methods: Derogenes ruber is redescribed based on newly collected specimens from the gall bladder of its type-host Chelidonichthys lastoviza (Bonnaterre, 1788) collected in the Western Mediterranean off the Algerian coast during 2017-2019 and molecular data are provided using a partial fragment of the nuclear 28S ribosomal RNA gene (28S rRNA), the internal transcribed spacer 2 (ITS2) and a fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene., Results: We herein provide a detailed illustrated redescription and morphometric data of D. ruber from its type-host C. lastoviza. We report a new geographical record (off Algeria) for it. Derogenes ruber is also genetically characterised for the first time. Species/lineages of Derogenes were recovered in five strongly supported reciprocally monophyletic clades: (i) D. ruber from C. lastoviza off Algeria; (ii) D. lacustris from Galaxias maculatus (Jenyns) off Argentina; (iii) Lineage "D. varicus DV1" (D. varicus sensu stricto) from fish hosts in the White and Barents seas and the North Sea; (iv) Lineage "D. varicus DV2" from mollusc hosts in the White Sea; and (v) Lineage "D. varicus DV3" from Eumicrotremus fedorovi Mandrytsa. in the Pacific Ocean. Hence, comparison of the newly generated sequences with other available data for Derogenes species supports the distinction of D. ruber confirming its taxonomic status and helping assess interspecific variation. Comparison of D. ruber with the closely related species Derogenes latus revealed overlaps in morphometric data and the validity of the latter species is questioned., Conclusion: The combination of morphological and molecular data provided for D. ruber provides a firm foundation for further investigations of Derogenes spp. Although we do describe herein material of D. ruber from the type-host, given that the occurrence of a single Derogenes species in various hosts has been challenged by molecular data, and both D. lacustris and D. varicus sensu stricto had been genetically proven to occur in various hosts, D. ruber and D. latus may be indeed synonymous. Additional sequencing effort on Derogenes spp. will strengthen systematic comparative studies and evolutionary relationships within the Derogenidae in general., (© 2023. The Author(s).)

Purpose: Species of the genus Philophthalmus are eye flukes with a complex taxonomy, which began to be improved with the help of molecular data only recently. However, most described species have never been placed into a phylogenetic context. In this study, eye flukes previously found on kelp gulls, Larus dominicanus, from Brazil and identified as Philophthalmus lacrymosus were subjected to molecular analysis., Methods: For the molecular analyses, we analyzed parasites found in six infected gulls (one worm per bird) collected from different municipalities of the state of Santa Catarina, Brazil. We carried out the amplification and sequencing of the partial region of the 28S and cox1 genes and the data obtained were compared with sequences available to philophthalmid species and subjected to phylogenetic analysis., Results: The isolates of P. lacrymosus from Brazil grouped in well-supported clades with five other species of Philophthalmus with sequences available for comparison. Interspecific divergences of 0.1-1.6% in 28S and 8.2-14.9% in cox1 were found in relation to other isolates of Philophthalmus spp. Two cox1 haplotypes differing in one nucleotide (0.1%) were found between the six eye flukes isolates in gulls from different localities. The Brazilian isolates grouped in a subclade with parasites identified as P. lacrymosus in Portugal; however, the molecular divergences found in cox1 (8.2-8.5%) strongly suggest that these isolates belong to different species. The phylogenetic trees obtained and the intergeneric divergences to species of the genera Cloacitrema and Parorchis did not support the validity of the genus Natterophthalmus, for which P. lacrymosus was proposed as the type species in the past., Conclusion: As P. lacrymosus was described from Brazil, we recommend that this name be applied to the South American isolates and that the Portuguese isolates be provisionally considered as Philophthalmus sp., a probable cryptic species. Moreover, data obtained supports the previous morphology-based synonymizing between Natterophthalmus and Philophthalmus. Considering our results and most of previous reports of P. lacrymosus in South America, we suggest this species presents a marine life cycle., (© 2023. The Author(s) under exclusive licence to Witold Stefański Institute of Parasitology, Polish Academy of Sciences.)

Species of Alestidae are known to be parasitised by dactylogyrid monogeneans representing three genera, Afrocleidodiscus Paperna, 1969, Annulotrema Paperna & Thurston, 1969, and Characidotrema Paperna & Thurston, 1968. The objective of the present study was to investigate the species diversity of Monopisthocotylea of African tetras from the Lower Phongolo River and floodplain in South Africa. Four new and two previously described species of Annulotrema were identified from the gills of three species of African tetras, Brycinus imberi, Hydrocynus vittatus, and Micralestes acutidens. The collected parasites were studied using two complementary approaches: morphology of hard sclerotised structures, and molecular markers using rDNA sequence data (28S rDNA, 18S rDNA, and ITS1). Three new species, Annulotrema arcum n. sp., Annulotrema caputfemoris n. sp., and Annulotrema strepsiceros n. sp., were described from B. imberi and one species, Annulotrema retortum n. sp., from M. acuditens. Two previously described species, Annulotrema pikoides Guégan, Lambert and Birgi, 1988 and A. pseudonili Kičinjaová and Řehulková, 2017, were newly recorded from H. vittatus in South Africa. Annulotrema arcum n. sp. and A. caputfemoris n. sp. share similar male copulatory organ morphologies, suggesting a close phylogenetic relationship as sister taxa. Despite weak nodal support, A. strepsiceros n. sp. shows morphological congruence with the former two species, reinforcing their molecular linkage. The present study shows a critical need for the exploration of monopisthocotylean diversity and the paucity of available molecular data of representatives from this group., (© M.L. Kičinjaová et al., published by EDP Sciences, 2024.)

We propose and describe Alobophora sandrae Cajiao-Mora & Bullard n. gen., n. sp. (Digenea: Caballerotrematidae) for specimens we collected from arapaima, Arapaima gigas sensu lato (Osteoglossiformes: Arapaimidae) in the Amazon River near Leticia, Colombia. Alobophora differs from Caballerotrema Prudhoe, 1960 by lacking head collar projections and by having clustered corner spines and a narrow head collar (4-5× wider than pharynx), whereas Caballerotrema has head collar projections, lacks clustered corner spines, and has a broad head collar (7-8× wider than pharynx). We reassign Caballerotrema annulatum (Diesing, 1850) Ostrowski de Núñez & Sattmann, 2002 to the new genus, as Alobophora annulata (Diesing, 1850) Cajiao-Mora and Bullard n. comb., and provide a supplemental description of Caballerotrema brasiliense Prudhoe, 1960 based on specimens we collected from arapaima. We also examined the holotype and a paratype of Caballerotrema piscicola (Stunkard, 1960) Kostadinova & Gibson, 2001 and concluded that C. piscicola is a junior subjective synonym of C. brasiliense. Our 28S phylogeny recovered A. sandrae sister to A. annulata, with that clade sister to a clade comprising C. brasiliense and an innominate species of Caballerotrema. Caballerotrematidae was recovered sister to Echinostomatidae. We also provide a dichotomous key to caballerotrematids based on head collar projections, corner spine arrangement, proportional pharynx and head collar breadth, testes shape and arrangement, body surface spine shape and distribution, vitellarium distribution, and abundance of prostatic cells., (© K. Cajiao-Mora et al., published by EDP Sciences, 2024.)

Several studies have shown that the euryxenic trematode Derogenes varicus (Müller, 1784) represents a species complex. Four lineages have been designated (DV1-4) with the DV1 clade corresponding to D. varicus sensu stricto. Herein, we investigate newly collected specimens of D. varicus sensu lato from Scandinavian and Arctic waters using integrative taxonomy. The trematodes were collected from Melanogrammus aeglefinus, Eutrigla gurnardus, Trachinus draco, and Merluccius merluccius off the Atlantic coast of Sweden and from Hippoglossoides platessoides from Arctic Svalbard. 28S sequences of derogenids from Sweden were identical to D. varicus sensu stricto, confirming its euryxeny. The 28S sequences of Derogenes sp. from H. platessoides were identical to Derogenes DV2 and differed from D. varicus sensu stricto by 3% and from Derogenes DV3 by 2%. The 28S sequence divergences of Derogenes sp. from H. platessoides with D. ruber and D. lacustris were 3 and 10%, respectively. ITS2 and cox1 divergences between Derogenes sp. from H. platessoides and other Derogenes species/lineages were at levels of interspecific differences. The species from H. platessoides is described here as D. abba n. sp. We also examined the type material of Progonus muelleri (Levinsen, 1881), the type and only species of the genus Progonus, with redescription and designations of paralectotypes. Based on specimens from Theodor Odhner's collections at the Swedish Museum of Natural History, SMNH, Stockholm, we provide novel morphological and anatomical data for D. varicus sensu lato species complex. Lastly, we investigated Arthur Looss's "lost collection" of Trematodes at the SMNH and characterised a putative species Derogenes sp. "limula"., (© C. Bouguerche et al., published by EDP Sciences, 2024.)

The platyhelminth class Trematoda comprises two subclasses with largely disparate species diversity, with the small Aspidogastrea with c.80 species and the speciose Digenea with c.18,000 species, which has attracted much effort towards our understanding of evolutionary relationships among suprageneric taxa. This chapter focuses on insights into the classification of the Digenea, that have become apparent from our advanced understanding of both morphological and molecular data. The field of molecular systematics of the Digenea has experienced significant advances over the past 15 years. Phylogenetic analyses of sequence data predominantly from the 18S and 28S rRNA genes have incorporated a considerable diversity of taxa, thus increasing the accuracy of phylogenetic inferences at higher taxonomic levels. As a result, the status of long-standing supraspecific taxa has been revised, new higher-level taxa have been defined, and inferences made in association with morphological and life-cycle evidence. A substantial effort has been made towards a classification reflecting a natural system of the Digenea by considering morphological evidence in conjunction with phylogenies inferred from molecular data; this has resulted in considerable congruence. However, limited taxon sampling in the phylogeny of the Digenea still remains relevant, especially in relation to some higher-level taxa, and an outline of these omissions is presented. A framework that has led to robust estimates of phylogeny is outlined, and the application of advanced morphological and molecular approaches in digenean taxonomy and systematics is illustrated using the most comprehensively studied digenean superfamilies., (© 2024. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

An integrative study was performed to understand the phylogenetic relationships of an undescribed, freshwater species of microcotylid parasitizing Plagioscion squamosissimus from the Amazon River Basin. Based on morphological and molecular analysis (18S rDNA and partial 28S rDNA genes), a new genus is proposed to accommodate this new species, Pauciconfibuloides amazonica gen. n. sp. n. The new genus is closely related to Protastomicrocotylinae and Pauciconfibula by sharing the vagina, male copulatory organ, and genital atrium all unarmed. However, Pauciconfibuloides gen. n. can be distinguished from those taxa by the prostatic system and position of the vaginal pore. Molecular phylogenetic inference suggests a sister relationship with species of Polylabris (Prostatomicrocotylinae), but to date, there are no available 18S or 28S rDNA sequences of Pauciconfibula to be compared. This is the first report of a microcotylid parasitizing a freshwater sciaenid from South America., (Copyright © 2021 Elsevier B.V. All rights reserved.)