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We herein describe Proterometra wigglewomble n. sp. (Digenea: Azygiidae: Azygiinae) from the Cahaba River, Alabama, USA, which asexually reproduces in the compact elimia, Elimia showalteri (Lea, 1860) (Cerithioidea: Pleuroceridae) and matures in the oesophagus of the blackbanded darter, Percina nigrofasciata (Agassiz, 1854) (Perciformes: Percidae). Adults of the new species differ from congeners by having a small body and eggs having a wholly fimbriated surface that appears as a cilia-like brush border. Live naturally-shed cercariae of the new species differ from those of its congeners by having a strongly claviform tail stem bearing aspinose mammillae, a single furca, excretory pores that open on the posterior margin of the single furca, and few eggs in the cercarial distome. The behaviour of the cercaria further differentiates the new species. Naturally-shed cercariae of P. wigglewomble secrete a jelly-like adhesive that coats the surface of the furca and evidently facilitates attachment to the surface of glass, plastic, and snail shell. Attached cercariae vigorously wiggle and thrash about once attached, as if mimicking the larva of a stream insect so as to lure the blackbanded darter to eat it. Phylogenetic analyses recovered monophyletic Azygiidae, comprising monophyletic Leuceruthrinae Goldberger, 1911 and polyphyletic Azygiinae Lühe, 1909. The present study is the largest taxon sampling for Azygiidae and the first to include 28S sequences of Leuceruthrus. Compact elimia and blackbanded darter are new host records for Proterometra. The new species is the 3 rd congener reported from the Cahaba River, a region renowned for its fish and snail endemic biodiversity., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Trematodes, or flukes, undergo intricate anatomical and behavioral transformations during their life cycle, yet the functional changes in their nervous system remain poorly understood. We investigated the molecular basis of nervous system function in Cryptocotyle lingua, a species of relevance for fisheries. Transcriptomic analysis revealed a streamlined molecular toolkit with the absence of key signaling pathways and ion channels. Notably, we observed the loss of nitric oxide synthase across the Platyhelminthes. Furthermore, we identified upregulated neuronal genes in dispersal larvae, including those involved in aminergic pathways, synaptic vesicle trafficking, TRPA channels, and surprisingly nitric oxide receptors. Using neuronal markers and in situ hybridization, we hypothesized their functional relevance to larval adaptations and host-finding strategies. Additionally, employing a behavior quantification toolkit, we assessed cercaria motility, facilitating further investigations into the behavior and physiology of parasitic flatworms. This study enhances our understanding of trematode neurobiology and provides insights for targeted antiparasitic strategies., (© 2023. The Author(s).)

Eurytrema coelomaticum , a pancreatic fluke, is recognized as a causative agent of substantial economic losses in ruminants. This infection, commonly referred to as eurytrematosis, is a significant concern due to its detrimental impact on livestock production. However, there is a paucity of knowledge regarding the mitochondrial genome of E. coelomaticum . In this study, we performed the initial sequencing of the complete mitochondrial genome of E. coelomaticum . Our findings unveiled that the mitochondrial genome of E. coelomaticum spans a length of 15,831 bp and consists of 12 protein-coding genes, 22 tRNA genes, two rRNA genes, and two noncoding regions. The A+T content constituted 62.49% of the genome. Moreover, all 12 protein-coding genes of E. coelomaticum exhibit the same arrangement as those of E. pancreaticum and other published species belonging to the family Dicrocoeliidae. The presence of a short string of additional amino acids (approximately 20~23 aa) at the N-terminal of the cox1 protein in both E. coelomaticum and E. pancreaticum mitochondrial genomes has contributed to the elongation of the cox1 gene in genus Eurytrema , surpassing that of all previously sequenced Dicrocoeliidae. The phylogenetic analysis displayed a close relationship between E. coelomaticum and E. pancreaticum , along with a genus-level association between Eurytrema and Lyperosomum . These findings underscore the importance of mitochondrial genomic data for comparative studies of Dicrocoeliidae and even Digenea, offering valuable DNA markers for future investigations in the systematic, epidemiological, and population genetic studies of this parasite and other digenean trematodes.

Six families belonging to the Paramphistomoidea superfamily have been reported in South America, with only Zonocotylidae and Balanorchiidae being endemic. The Zonocotylidae was initially classified as Aspidogastrea and then as a paramphistomoid. This family comprises a single genus, Zononocotyle , with two species. It is primarily characterized by having an attachment organ with transverse ridges and a single testis. The placement of Zonocotylidae within Paramphistomoidea is controversial, as some researchers speculate that this genus is the most primitive member of the superfamily, while others consider it an aberrant form. The main objectives of our study were to provide the first sequences of Zonocotylidae and elucidate its phylogenetic position. We amplified the 28S gene from two parasites from Cyphocharax sp. from Punta Lara, Buenos Aires. Newly generated sequences were used to infer the phylogenetic relationships with other Paramphistomoidea species using a Bayesian approach. Zonocotylidae were clustered with Dadayiinae and Kalitrematinae (Cladorchiidae) species found in freshwater fishes from South America. Genetic analyses revealed that they formed a well-supported clade with cladorchiids in freshwater hosts from South America. However, the occurrence of genera of Cladorchiidae in North America, Middle America, Asia, and Australia suggested its polyphyletic nature and may indicate the need for the erection of new families. Other Paramphistomoidea families may also require further revision. The addition of new sequences to phylogenetic analyses along with a comprehensive and more detailed description of the genera will help resolve the relationships within this group.

Philopinna higai is a species of Didymozoidae (Digenea: Hemiuroidea). The definitive hosts of this parasite only belong to the fish genus Sarcocheilichthys. Sarcocheilichthys fishes are endemic to Lake Biwa and southwestern Japan and were introduced into the northeastern (Tohoku) region. However, P. higai parasitism has not been investigated in the Tohoku region. In this study, we surveyed the distribution of P. higai in the Tohoku region and sequenced 28S rDNA (994 bp) and cytochrome oxidase subunit 1 (CO1) gene (721 bp) of P. higai. We also sequenced mitochondrial cytochrome b (581 bp) of Sarcocheilichthys fishes from the Tohoku region and Lake Biwa. Our findings confirmed the distribution of P. higai in all seven surveyed river systems in the four prefectures of the Tohoku region. The 28S rDNA sequence of P. higai did not differ among regions, whereas 10 haplotypes of CO1 were identified and clustered into two major clades. The haplotypes of Sarcocheilichthys fishes introduced in the Tohoku region were identical to the dominant haplotypes in Lake Biwa. Thus, P. higai from Lake Biwa and the Tohoku region were genetically the same species, although genetically differentiated populations formed in the Tohoku region., Competing Interests: Declaration of Competing Interest None., (Copyright © 2023. Published by Elsevier B.V.)

This study aimed to enhance our understanding in monogenoid evolution by using morphological and molecular data to determine kinship relationships between species and changes in morphological structures over time. We focused on variations in characteristics among the organisms of the family Gyrodactylidae, concentrating on the phylogenetic position of Polyclithrum with other genera in the family. We collected specimens of Polyclithrum from the striped mullet, Mugil cephalus and Swingleus, and Fundulotrema specimens from mummichog Fundulus heteroclitus in estuarine systems of South Carolina, United States. In addition, we analyzed them and other genera (including e.g., Mormyrogyrodactylus, Gyrodactyloides, and Macrogyrodactylus) using both morphological and molecular (18S rDNA) approaches. We performed phylogenetic trees based on Maximum Parsymony, Maximum Likelihood and Bayesian Inference, and constructed a character morphological matrix by Parsimony Reconstruction of Ancestral Character States method. Our results suggest a homoplastic origin with evolutionary convergences in characters, revealing that there is inconsistency between our data and previously published works based solely on morphological structures of the group. The homoplasy scenario found in Gyrodactylidae can be a result of the limited set of putative homologous morphological features. However, differences between the phylogenies based on morphology and those based on molecular data may arise from both databases. While morphology remains essential in understanding the evolution of this group, molecular data, otherwise, provide a less biased source of information for constructing phylogenetic hypotheses. Combining these data facilitates a better comprehension of the homologous status of morphological features and to understand Gyrodactylidae evolutionary history., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

With one exception, the only known hemiurid trematodes that do not use teleost fishes as definitive hosts instead occur in marine elapid snakes. These comprise six species across four genera and three subfamilies, and so presumably indicate at least three independent invasions of marine snakes from teleost fishes. Here, one of these taxa, Tubulovesicula laticaudi Parukhin, 1969 (= T. orientalis Chattopadhyaya, 1970 n. syn.) is reported from Sri Lanka, collected from Shaw's sea snake Hydrophis curtus (Shaw) (Elapidae: Hydrophiinae: Hydrophinii), the annulated sea snake H. cyanocinctus Daudin and the yellow sea snake H. spiralis (Shaw) off Nayaru in the Bay of Bengal, and from H. spiralis in Portugal Bay, Gulf of Mannar. Novel molecular data, for COI mtDNA and ITS2 and 28S rDNA, are the first for a species of Tubulovesicula Yamaguti, 1934. Nominally, Tubulovesicula belongs in the Dinurinae Looss, 1907, but in phylogenetic analyses based on 28S rDNA, our sequences for T. laticaudi resolved relatively distant from that for representatives of Dinurus Looss, 1907, the type-genus, rendering the subfamily polyphyletic. Tubulovesicula laticaudi resolved closest to data for the type-species of the Plerurinae Gibson & Bray, 1979, but that subfamily is also polyphyletic. These findings lead us to re-evaluate an alternative classification considered by Gibson & Bray (1979). We propose restricting the Dinurinae for forms with a permanent sinus-organ (Dinurus, Ectenurus Looss, 1907; Erilepturus Woolcock, 1935; Paradinurus Vigueras, 1958; Qadriana Bilqees, 1971) and resurrect the Mecoderinae Skrjabin & Guschanskaja, 1954 for forms with a temporary sinus-organ (Mecoderus Manter, 1940, Allostomachicola Yamaguti, 1958, Stomachicola Yamaguti, 1934 and Tubulovesicula)., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Two species of Pseudodiscocotyla Yamaguti, 1965 (Monogenea: Discocotylidae) were collected from crimson jobfish Pristipomoides filamentosus (Valenciennes) (Perciformes: Lutjanidae) off Okinawa-jima island, southern Japan. Pseudodiscocotyla opakapaka is redescribed and represents the first Japanese record. A new species, Pseudodiscocotyla mikiae n. sp., differs from Ps. opakapaka in the absence of spines around the male genital pore, the shape of the vaginal pore, the presence of spines inside the vaginal pore, and the shape of the clamp. The locations of the male genital atrium and the vaginal pore in both species were similar, and the observed armament differences of the male copulatory organ are therefore presumed to establish reproductive isolation. The phylogenetic trees for the Mazocraeidea based on the partial 28S rDNA sequences were created using new sequences of Pseudodiscocotyla mikiae n. sp., and Discocotylidae formed a sister group with the species Diclidophoridae, Macrovalvitrematidae, and Plectanocotylidae. Pristipomoides filamentosus is widely distributed across the Indo-Pacific, and Pseudodiscocotyla mikiae n. sp. could share the distribution of the host., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

In South America, the knowledge of trematode diversity parasitizing freshwater fishes is still scarce, as less than 5% of the freshwater fish fauna has been examined for parasites. A similar situation applies to studies on digenean life cycles, which have become increasingly rare. Among the digenean families parasitizing freshwater fishes in the region, Haploporidae is considered the richest in species diversity. However, information about the developmental stages of haploporid life cycles remains fragmentary. Particularly, in Argentina, nine cercariae attributed to the family Haploporidae have been described using morphological analysis, and only two life cycles of this family have been completely elucidated. In this study a new type of cercaria, morphologically assigned to the family Haploporidae and collected from the snail Heleobia parchappii (Cochliopidae) in Los Padres shallow lake, Buenos Aires province, was identified using morphological and molecular techniques. The molecular analysis, based on 28S and ITS2 sequences, revealed that the cercariae were 100% identical to adult specimens of Saccocoelioides nanii (Haploporidae) parasitizing the fish Prochilodus lineatus (Prochilodontidae) from Los Talas, Buenos Aires province. Our results not only provide information about the life cycle of S. nanii but also show that a molecular and morphological approach can be extremely useful in identifying the developmental stages of digeneans and elucidating their life cycles.

This study characterized novel RNA viruses, parasites of parasites, or hyperparasites identified during transcriptomic analyses of two trematode species, Cryptocotyle lingua and Himasthla elongata, infecting a sea snail, Littorina littorea. According to the viral genome structures and phylogenetic analysis, Cryptolin alternavirus (ClRNAV1), Cryptolin calicivirus (ClRNAV2) and Himastelon rhabdovirus 1 (HeRNAV1) were respectively classified within the families Alternaviridae, Caliciviridae and Rhabdoviridae. They replicate species-specifically in two studied phases of trematode live cycle: intramolluscan parthenogenetic rediae and free-swimming cercariae. ClRNAV1 showed significantly higher expression in C. lingua cercariae relative to rediae. HeRNAV1's similarity to rabies viruses raises questions about its potential effects on the nervous system of H. elongata. This 'trematode rabies' could enable the use of genetically modified viruses for developing new methods to control the spread and intensity of diseases caused by trematodes., 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 © 2023 Elsevier Inc. All rights reserved.)

Multiple parasites can infect a single host, creating a dynamic environment where each parasite must compete over host resources. Such interactions can cause greater harm to the host than single infections and can also have negative consequences for the parasites themselves. In their first intermediate hosts, trematodes multiply asexually and can eventually reach up to 20% of the host's biomass. In most species, it is unclear whether this biomass results from a single infection or co-infection by 2 or more infective stages (miracidia), the latter being more likely a priori in areas where prevalence of infection is high. Using as model system the trematode Bucephalus minimus and its first intermediate host cockles, we examined the genetic diversity of the cytochrome c oxidase subunit I region in B. minimus from 3 distinct geographical areas and performed a phylogeographic study of B. minimus populations along the Northeast Atlantic coast. Within localities, the high genetic variability found across trematodes infecting different individual cockles, compared to the absence of variability within the same host, suggests that infections could be generally originating from a single miracidium. On a large spatial scale, we uncovered significant population structure of B. minimus , specifically between the north and south of Bay of Biscay. Although other explanations are possible, we suggest this pattern may be driven by the population structure of the final host.

Invasive Nile tilapias negatively impact native tilapia species through hybridisation and competition. However, the co-introduction of parasites with Nile tilapia, and subsequent changes in parasite communities, are scarcely documented. Monogeneans are known pathogens of cultured Nile tilapia, although little is known about their fate once Nile tilapias establish in new ecosystems. We investigate the parasitological consequences of Nile tilapia introduction on native tilapias in basins in Cameroon, the Democratic Republic of the Congo (DRC), and Zimbabwe, focusing on ectoparasitic dactylogyrids (Monogenea). Using the mitochondrial cytochrome oxidase c subunit I (COI) and nuclear 18S-internal transcribed spacer 1 (18S-ITS1) rDNA region of 128 and 166 worms, respectively, we evaluated transmission of several dactylogyrid species. Parasite spillover from Nile tilapia was detected for Cichlidogyrus tilapiae to Coptodon guineensis in Cameroon, Cichlidogyrus thurstonae to Oreochromis macrochir in the DRC, and Cichlidogyrus halli and C. tilapiae to Coptodon rendalli in Zimbabwe. Parasite spillback to Nile tilapia was detected for Cichlidogyrus papernastrema and Scutogyrus gravivaginus from Tilapia sparrmanii and Cichlidogyrus dossoui from C. rendalli or T. sparrmanii in the DRC, and Cichlidogyrus chloeae from Oreochromis cf. mortimeri and S. gravivaginus from O. macrochir in Zimbabwe. 'Hidden' transmissions (i.e. transmission of certain parasite lineages of species that are naturally present on both alien and native hosts) were detected for C. tilapiae and Scutogyrus longicornis between Nile tilapia and Oreochromis aureus and C. tilapiae between Nile tilapia and Oreochromis mweruensis in the DRC, and Cichlidogyrus sclerosus and C. tilapiae between Nile tilapia and O. cf. mortimeri in Zimbabwe. A high density of Nile tilapia occurring together with native tilapias, and the broad host range and/or environmental tolerance of the transmitted parasites, are proposed as factors behind parasite transmission through ecological fitting. However, continuous monitoring and the inclusion of environmental variables are necessary to understand the long-term consequences of these transmissions on native tilapias and to elucidate other underlying factors influencing these transmissions., (Copyright © 2023 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.)

Trematodes can adversely impact the health and survival of wild animals. The trematode family Cyclocoelidae, which includes large digenean bird parasites, lacks molecular analysis, and reclassifications have not been supported. This study produced the first fully assembled and annotated mitochondrial genome sequence for the trematode Morishitium polonicum. The whole length of the M. polonicum (GenBank accession number: OP930879) mitogenome is 14083 bp, containing 22 transfer ribonucleic acids (tRNAs), 2 ribosomal RNAs (rRNAs, rrnL and rrnS), and a noncoding control section (D-loop) 13777 to 13854 bp in length. The 12 PCG areas have 3269 codons and a total length of 10053 bp, which makes up 71.38% of the mitochondrial genome ' s overall sequence. Most (10/12) of the PCGs that code for proteins begin with ATG, while the nad4L and nad1 genes have a GTG start codon. Phylogenetic analysis using the concatenated nucleotide sequences of 12 PCGs, and the ML tree analysis results showed that M. polonicum is more closely related to with Echinostomatidae and Fasciolidae, which indicates that the family Cyclocoelidae is more closely associated with Echinochasmidae. This study provides mtDNA information, and analysis of mitogenomic structure and evolution. Moreover, we aimed to understand the phylogenetic relationships of this fluke., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Parasites have evolved a variety of astonishing strategies to survive within their hosts, yet the most challenging event in their personal chronicles is the passage from one host to another. It becomes even more complex when a parasite needs to pass through the external environment. Therefore, the free-living stages of parasites present a wide range of adaptations for transmission. Parasitic flatworms from the group Digenea (flukes) have free-living larvae, cercariae, which are remarkably diverse in structure and behavior. 1 , 2 One of the cercariae transmission strategies is to attain a prey-like appearance for the host. 3 This can be done through the formation of a swimming aggregate of several cercariae adjoined together by their tails. 4 Through the use of live observations and light, electron, and confocal microscopy, we described such a supposedly prey-mimetic colony comprising cercariae of two distinct morphotypes. They are functionally specialized: larger morphotype (sailors) enable motility, and smaller morphotype (passengers) presumably facilitate infection. The analysis of local read alignments between the two samples reveals that both cercaria types have identical 18S, 28S, and 5.8S rRNA genes. Further phylogenetic analysis of these ribosomal sequences indicates that our specimen belongs to the digenean family Acanthocolpidae, likely genus Pleorchis. This discovery provides a unique example and a novel insight into how morphologically and functionally heterogeneous individuals of the same species cooperate to build colonial organisms for the purpose of infection. This strategy bears resemblance to the cooperating castes of the same species found among insects. 5 ., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Notocotylus cygni n. sp. is described here, taken from the intestine of the black-necked swan Cygnus melancoryphus (Molina) of Patagonia, Argentina. This new species differs from other members of the genus Notocotylus by having the genital pore anterior to the caecal bifurcation (located slightly posterior to oral sucker) and the unequal number and arrangement of ventral papillae (2-3 in the lateral rows and 10-12 in the median row). Phylogenetic analyses of the 28S and ITS1-5.8S ribosomal DNA (rRNA) sequences of the new species and other notocotylid trematodes available in GenBank indicate that N. cygni n. sp. is a sister taxon of Notocotylus fosteri Kinsella et Tkach, 2005, a trematode of the intestine of the rice rat Oryzomys palustris of Florida, United States. The new species differs from N. fosteri in the unequal number and arrangement of ventral papillae, number of uterine loops, size of the egg, definitive hosts (birds vs. mammals), and disparate environment and geographical distribution (freshwater environment in Patagonia vs. salt marsh in North America). This is the eighth species of Notocotylus reported from birds in Argentina, and the ninth species from the family Notocotylidae recorded in black-necked swans in South America., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The concept that microbes associated with macroorganisms evolve as a unit has swept evolutionary ecology. However, this idea is controversial due to factors such as imperfect vertical transmission of microbial lineages and high microbiome variability among conspecific individuals of the same population. Here, we tested several predictions regarding the microbiota of four trematodes (Galactosomum otepotiense, Philophthalmus attenuatus, Acanthoparyphium sp. and Maritrema novaezealandense) that parasitize the same snail host population. We predicted that each parasite species would harbour a distinct microbiota, with microbial composition similarity decreasing with increasing phylogenetic distance among parasite species. We also predicted that trematode species co-infecting the same individual host would influence each other's microbiota. We detected significant differences in alpha and beta diversity, as well as differential abundance, in the microbiota of the four trematode species. We found no evidence that phylogenetically closely related trematodes had more similar microbiota. We also uncovered indicator bacterial taxa that were significantly associated with each trematode species. Trematode species sharing the same snail host showed evidence of mostly one-sided bacterial exchanges, with the microbial community of one species approaching that of the other. We hypothesize that natural selection acting on specific microbial lineages may be important to maintain differences in horizontally acquired microbes, with vertical transmission also playing a role. In particular, one trematode species had a more consistent and diverse bacteriota than the others, potentially a result of stronger stabilizing pressures. We conclude that species-specific processes shape microbial community assembly in different trematodes exploiting the same host population., (© 2023 The Authors. Molecular Ecology published by John Wiley & Sons Ltd.)

The trematode Postharmostomum commutatum is a parasite of the chicken Gallus gallus domesticus. Its heavy infection can cause inflammation and hemorrhage in the cecum of host birds. We found a severe infection of metacercariae of P. commutatum, which was identified based on DNA barcodes with morphology, in the introduced land snail Bradybaena pellucida and its related species in the Kanto region of Japan. Our field survey revealed that metacercariae were detected in 14 of 69 sampling locations in this region. B. pellucida was thought to be the major second intermediate host of metacercariae of the trematode because this snail was most frequently found in the study area and the prevalence and infection intensity were higher than those of the other snail species. The observed increase in metacercariae in introduced populations of B. pellucida can enhance the infection risk of chickens and wild host birds, probably owing to the spillback effect. Our seasonal field study showed that the prevalence and infection intensity of metacercaria seemed to be high in populations of B. pellucida during the summer and early autumn. Therefore, chickens should not be bred outdoors during these seasons to prevent severe infection. Our molecular analysis, based on cytochrome c oxidase subunit I sequences, showed a significantly negative value for Tajima's D in P. commutatum, suggesting an increase in its population size. Thus, P. commutatum distributed in the Kanto region may have increased its population size with the introduction of the host snail., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Manipulation of host phenotypes by parasites is hypothesized to be an adaptive strategy enhancing parasite transmission across hosts and generations. Characterizing the molecular mechanisms of manipulation is important to advance our understanding of host-parasite coevolution. The trematode (Levinseniella byrdi) is known to alter the colour and behaviour of its amphipod host (Orchestia grillus) presumably increasing predation of amphipods which enhances trematode transmission through its life cycle. We sampled 24 infected and 24 uninfected amphipods from a salt marsh in Massachusetts to perform differential gene expression analysis. In addition, we constructed novel genomic tools for O. grillus including a de novo genome and transcriptome. We discovered that trematode infection results in upregulation of amphipod transcripts associated with pigmentation and detection of external stimuli, and downregulation of multiple amphipod transcripts implicated in invertebrate immune responses, such as vacuolar ATPase genes. We hypothesize that suppression of immune genes and the altered expression of genes associated with coloration and behaviour may allow the trematode to persist in the amphipod and engage in further biochemical manipulation that promotes transmission. The genomic tools and transcriptomic analyses reported provide new opportunities to discover how parasites alter diverse pathways underlying host phenotypic changes in natural populations., (© 2023 The Authors. Molecular Ecology published by John Wiley & Sons Ltd.)

In recent field studies, suspected gymnophallid metacercariae were histologically located in the mantle of mussels from the Norwegian Sea. Mussels from the sites in which that infection was detected also presented abnormally high pearl numbers. It has been previously described that gymnophallid metacercariae could cause pearl formation processes in mussels, as a host reaction to encapsulate these metacercariae. Given the pathological host reaction these parasites elicit, a study was performed to identify gymnophallid metacercariae found in mussels collected from Tromsø at morphological and molecular level and to assess, by the use of molecular tools, the relationship between the parasite and the biological material inside the pearls. As a result, Gymnophallus bursicola metacercariae infecting Norwegian Mytilus edulis were identified according to morphological characters, along with the first 18S rDNA and COI sequences for this trematode species. In addition, parasite DNA from the core of the pearls was extracted and amplified for the first time, confirming the parasitological origin of these pearls. This procedure could allow identifying different parasitic organisms responsible for the generation of pearls in bivalves.

The family Cyathocotylidae trematode is a world-widely distributed parasite whose adults are mainly found in fish, reptiles, birds, and mammals in both freshwater and marine environments. However, little is known of the prevalence of these trematode in China. For the first time, we found Cyathocotylidae trematode in the Wuhu area. Therefore, we investigated the prevalence of metacercariae in Carassius auratus from Zhang Lake, Kui Lake, Qingyi River, and Yangtze River (Wuhu Section) in Wuhu area. A total of 392 one-year-old C. auratus were tested in January, April, July, and October 2019, respectively. After the fish were euthanized, the back, chest, and tail muscles were used for preliminary screening for the presence of metacercariae by direct compression method. Metacercariae were isolated by the artificial digestion method and then morphologically and molecularly identified by cox1 (642 bp) and ITS2 (418 bp) sequences amplification by PCR. Based on morphological features and sequence analysis, they were identified as cyathocotylid metacercariae. The four water sources have different degrees of prevalence throughout the year, the prevalence ranges from 28.45% (29/102) in Yangtze River to 50.55% (46/91) in Zhang Lake, with an average prevalence of 40.56% (159/392). There were also differences in the prevalence in different months: The highest occurred in July, which was 81.63% (80/98), while the lowest occurred in January, which was 8.89% (8/90). This study can provide basic data for the prevention and control of cyathocotylid trematode in this area., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

New data on the complete mitochondrial genome of Azygia robusta (Azygiidae) were obtained by the next-generation sequencing (NGS) approach. The mitochondrial DNA (mtDNA) of A. robusta had a length of 13 857 bp and included 12 protein-coding genes, two ribosomal genes, 22 transfer RNA genes, and two non-coding regions. The nucleotide sequences of the complete mitochondrial genomes of two A. robusta specimens differed from each other by 0.12 ± 0.03%. Six of 12 protein-coding genes demonstrated intraspecific variation. The difference between the nucleotide sequences of the complete mitochondrial genomes of A. robusta and Azygia hwangtsiyui was 26.95 ± 0.35%; the interspecific variation of protein-coding genes between A. robusta and A. hwangtsiyui ranged from 20.5 ± 0.9% ( cox 1) to 30.7 ± 1.2% ( nad 5). The observed gene arrangement in the mtDNA sequence of A. robusta was identical to that of A. hwangtsiyui. Codon usage and amino acid frequencies were highly similar between A. robusta and A. hwangtsiyui. The results of phylogenetic analyses based on mtDNA protein-coding regions showed that A. robusta is closely related to A. hwangtsiyui (belonging to the same suborder, Azygiida) that formed a distinct early-diverging branch relative to all other Digenea. A preliminary morphological analysis of paratypes of the two azygiid specimens studied showed visible morphological differences between them. The specimen extracted from Sakhalin taimen ( Parahucho perryi ) was most similar to A. robusta. Thus, we here provide the first record of a new definitive host, P. perryi , for A. robusta and also molecular characteristics of the trematode specimens.

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

Eight species (four new) of Urocleidoides are reported from Characiformes and Gymnotiformes fishes of the coastal drainages of the Eastern Amazon. Urocleidoides vanini n. sp. is characterized by having a male copulatory organ (MCO) with three and a half counterclockwise rings, absence of vaginal sclerite, and a V-shaped ventral bar. Urocleidoides atilaiamarinoi n. sp. has MCO with two and a half counterclockwise rings, dumbbell-shaped accessory piece, similar anchors, open V-shaped ventral bar, and open U-shaped dorsal bar. Urocleidoides macrosoma n. sp. exhibits an elongate and robust body, MCO comprising one counterclockwise ring, similar anchors with wavy point, and dumbbell-shaped ventral and dorsal bars. Urocleidoides nataliapasternakae n. sp. has MCO comprising two and a half counterclockwise rings, vaginal canal convoluted, point of the dorsal anchor with ornamentation as sclerotized shredded filaments, elongate dumbbell-shaped ventral bar, and U-shaped dorsal bar. Urocleidoides naris and Urocleidoides brasiliensis from H. malabaricus (Characiformes) and the incertae sedis species, Urocleidoides gymnotus and Urocleidoides carapus , from Sternopygus macrurus (Gymnotiformes) are reported, and their molecular sequences are presented in this study. Phylogenetic analyses based on molecular data (28S rDNA and COI mtDNA) reveal that species of Urocleidoides lacking vaginal sclerite are closely related to species that possess vaginal sclerite, suggesting that the absence of vaginal sclerite in Urocleidoides may be the result of a secondary loss. The relationships between species of Urocleidoides and other Neotropical dactylogyrids are also addressed.

The prevalence of infection with trematode parthenitae was studied in Littorina obtusata littoral periwinkles with different shell color genotypes. Activities of genes responsible for a purple or orange single-pigment background shell coloration was not found to affect the prevalence of trematode infection in periwinkles. In L. obtusata with a yellow-purple background shell color and a pattern of white pigment spots on the shell, the prevalence of infection with Microphallus piriformes and M. pygmaeus was lower than the theoretical expectation. The prevalence of infection in periwinkles with purple, orange, or white stripes on the shell did not differ from that of unstripped periwinkles. The differences found were presumably associated with genetically determined susceptibility to infection. Possible consequences of differential infection with trematodes in periwinkles with different shell color genotypes are discussed in terms of the stability of parasitic systems and possible changes in the phenotypic structure of the host population., (© 2023. Pleiades Publishing, Ltd.)

There is limited information about the species of rumen fluke (Family Paramphistomidae) in the Caribbean. However, knowledge of species distribution is needed to better understand disease risk and epidemiology. Morphological identification is challenging with more recent DNA sequencing enabling a better understanding of rumen fluke distribution. In this study, rumen fluke specimens, collected between 2015 and 2016 from cattle on the island of St. Kitts, West Indies, were analysed. The ribosomal internal transcribed spacer 2 (ITS-2) region of rDNA was amplified using generic trematode primers. Results from Sanger sequencing were compared to reference sequences in GenBank and indicated the species was Cotylophoron cotylophorum with 100% sequence identity and 91% query cover. The ITS2 sequences were then compared to previously published ITS2 sequences for the Cotylophoron genus. When all the St. Kitts C. cotylophorum ITS2 sequences were compared with all other Cotylophoron sequences from India, Kenya, and Zimbabwe, three variable nucleotide sites, resulting in five unique haplotypes, were identified. Nine ITS2 sequences shared haplotype 1, which included all those from St. Kitts and single representatives from India and Kenya, potentially indicating global movement of this species., Competing Interests: Declaration of Competing Interest The authors declare that there were no conflicts of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A Leucochloridium sp. Carus, 1835 sporocyst with a mature colored broodsac was found in a Succinea putris L., 1758 snail in the Boksitogorsk district of Leningrad Region (Russia). The pigmentation of the sporocyst's broodsac was different from those of other Leucochloridium Carus, 1835 species previously described for Europe. The obtained sporocyst is most similar by the coloration of its broodsac to the trematodes of the same genus from Japan. The genotyping of the investigated sporocyst by the rDNA gene fragments (complete ITS1, ITS2, 5.8S and partial 18S and 28S sequences) was conducted. Genetic distances between the obtained sporocyst and the previously described species of the genus Leucochloridium were higher than intraspecific ones in the most cases. These data and the data of morphological analysis imply that the investigated sporocyst belongs to a separate species of the Leucochloridium genus, previously not described in the European region., (© 2023. Pleiades Publishing, Ltd.)

Plagiorchis multiglandularis Semenov, 1927 is a common fluke of birds and mammals, with significant impacts on animals and also human health. However, the systematics of Plagiorchiidae remain ambiguous. In the present study, the complete mitochondrial (mt) genome of P. multiglandularis cercariae was sequenced and compared with other digeneans in the order Xiphidiata. The complete circular mt genome of P. multiglandularis was 14,228 bp in length. The mitogenome contains 12 protein-coding genes and 22 transfer RNA genes. The 3' end of nad4L overlaps the 5' end of nad4 by 40 bp, while the atp8 gene is absent. Twenty-one transfer RNA genes transcribe products with conventional cloverleaf structures, while one transfer RNA gene has unpaired D-arms. Comparative analysis with related digenean trematodes revealed that A + T content of mt genome of P. multiglandularis was significantly higher among all the xiphidiatan trematodes. Phylogenetic analyses demonstrated that Plagiorchiidae formed a monophyletic branch, in which Plagiorchiidae are more closely related to Paragonimidae than Prosthogonimidae. Our data enhanced the Plagiorchis mt genome database and provides molecular resources for further studies of Plagiorchiidae taxonomy, population genetics and systematics., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The complete mitogenome (mtDNA) of nominal Paragonimus iloktsuenensis (Paragonimidae: Trematoda) and the nuclear ribosomal transcription unit (rTU) coding region (rTU*: from 5'-terminus of 18S to 3'-terminus of 28S rRNA gene, excluding the external spacer region) of this species and of P. ohirai were obtained and used to further support the previously suggested synonymy of these taxa in the P. ohirai complex. The complete mitogenome of P. iloktsuenensis was 14,827 bp long (GenBank: ON961029) and nearly identical to that of P. ohirai (14,818 bp; KX765277), with a 99.12% nucleotide identity. The rTU* was 7543 bp and 6932 bp in these two taxa, respectively. All genes and spacers in the rTU were identical in length, with exception of the first internal transcribed spacer, which contained multiple tandem repeat units (6.7 for P. iloktsuenensis and 5.7 for P. ohirai). There was near 100% identity for the rTU genes. The phylogenetic topology inferred from the mtDNA and from individual gene regions (partial cox1 of 387 bp and the ITS-2 of 282 bp - 285 bp) indicated a very close relationship consistent with synonymy of P. iloktsuenensis and P. ohirai. The datasets provided here will be useful for taxonomic reappraisal as well as studies of evolutionary and population genetics of the genus Paragonimus and family Paragonimidae., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Trematodes of the genus Ogmocotyle are intestinal flukes that can infect a variety of definitive hosts, resulting in significant economic losses worldwide. However, there are few studies on molecular data of these trematodes. In this study, the mitochondrial (mt) genome of Ogmocotyle ailuri isolated from red panda ( Ailurus fulgens ) was determined and compared with those from Pronocephalata to investigate the mt genome content, genetic distance, gene rearrangements and phylogeny. The complete mt genome of O. ailuri is a typical closed circular molecule of 14 642 base pairs, comprising 12 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes and 2 non-coding regions. All genes are transcribed in the same direction. In addition, 23 intergenic spacers and 2 locations with gene overlaps were determined. Sequence identities and sliding window analysis indicated that cox 1 is the most conserved gene among 12 PCGs in O. ailuri mt genome. The sequenced mt genomes of the 48 Plagiorchiida trematodes showed 5 types of gene arrangement based on all mt genome genes, with the gene arrangement of O. ailuri being type I. Phylogenetic analysis using concatenated amino acid sequences of 12 PCGs revealed that O. ailuri was closer to Ogmocotyle sikae than to Notocotylus intestinalis . These data enhance the Ogmocotyle mt genome database and provide molecular resources for further studies of Pronocephalata taxonomy, population genetics and systematics.

Some parasites manipulate their host's phenotype to enhance predation rates by the next host in the parasite's life cycle. Our understanding of this parasite-increased trophic transmission is often stymied by study-design challenges. A recurring difficulty has been obtaining uninfected hosts with a coevolutionary history with the parasites, and conducting experimental infections that mimic natural processes. In 1996, Lafferty and Morris provided what has become a classic example of parasite-increased trophic transmission; they reported a positive association between the intensity of a brain-infecting trematode (Euhaplorchis californiensis) in naturally infected California killifish (Fundulus parvipinnis) and the frequency of conspicuous behaviors, which was thought to explain the documented 10-30× increase in predation by the final host birds. Here, we address the primary gap in that study by using experimental infections to assess the causality of E. californiensis infection for increased conspicuous behaviors in F. parvipinnis. We hatched and reared uninfected F. parvipinnis from a population co-occurring with E. californiensis, and infected them 1-2 times/week over half their life span with E. californiensis and a small cyathocotylid trematode (SMCY) that targets the host's muscle tissue. At 3 time points throughout the hosts' lives, we quantified several conspicuous behaviors: contorting, darting, scratching, surfacing, and vertical positioning relative to the water's surface. Euhaplorchis californiensis and SMCY infection caused 1.8- and 2.5-fold overall increases in conspicuous behaviors, respectively. Each parasite was also associated with increases in specific conspicuous behaviors, particularly 1.9- and 1.4-fold more darting. These experimental findings help solidify E. californiensis-F. parvipinnis as a classic example of behavioral manipulation. Yet our findings for E. californiensis infection-induced behavioral change were less consistent and strong than those previously documented. We discuss potential explanations for this discrepancy, particularly the idea that behavioral manipulation may be most apparent when fish are actively attacked by predators. Our findings concerning the other studied trematode species, SMCY, highlight that trophically transmitted parasites infecting various host tissues are known to be associated with conspicuous behaviors, reinforcing calls for research examining how communities of trophically transmitted parasites influence host behavior., (© American Society of Parasitologists 2023.)

Lymnaeid snails play a crucial role in the transmission of trematode cercariae as an intermediate host that can infect humans, ruminants like buffalo, and other animals, resulting in serious economic losses. The purpose of the study was to identify the morphological and molecular characteristics of snails and cercariae collected from water bodies near buffalo farms that were integrated with palm oil in Perak, Malaysia. The presence or absence of snails in 35 water bodies was examined via cross-sectional study. From three marsh wetlands, 836 lymnaeid snails were gathered in total. Each snail's shell was morphologically identified to determine its family and species. The cercarial stage inside each snail's body was observed using the crushing method and trematode cercariae types were determined. In addition, the target gene Cytochrome c oxidase subunit 1 (Cox1) and the ribosomal internal transcribed spacer 2 (ITS2) region were used to identify the snail species and cercarial types according to the species level. The findings indicated that the collected snails belong to the family lymnaeidae and Radix rubiginosa species. In snails, the cercarial emergence infection rate was 8.7%. Echinostome, xiphidiocercariae, gymnocephalous, brevifurcate-apharyngeate distome cercariae (BADC), and longifurcate-pharyngeal monostome cercariae (LPMC) are the five morphological cercarial types that were observed. The cercariae were identified using morphological and molecular techniques, and they are members of the four families which are Echinostomatidae, Plagiorchiidae, Fasciolidae, and Schistosomatidae. Interestingly, this is the first study on R. rubiginosa and several trematode cercariae in Perak water bodies near buffalo farms that are integrated with palm oil. In conclusion, our research shown that a variety of parasitic trematodes in Perak use R. rubiginosa as an intermediate host., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Diplozoidae are common monogenean ectoparasites of cyprinoid fish, with the genus Paradiplozoon being the most diversified. Despite recent studies on Diplozoidae from Europe, Africa and Asia, the diversity, distribution and phylogeny of this parasite group appears to be still underestimated in the Middle East. The objective of this study was to investigate the diversity, endemism and host specificity of diplozoids parasitizing cyprinoid fish from the Middle East, considering this region as an important historical interchange of fish fauna, and to elucidate the phylogenetic position of Middle Eastern Paradiplozoon species within Diplozoidae. Four Paradiplozoon species were collected from 48 out of 94 investigated cyprinoid species. Three known species, Paradiplozoon homoion , Paradiplozoon bliccae and Paradiplozoon bingolensis , were recorded on new cyprinoid host species, and a new species, Paradiplozoon koubkovae n. sp., was recorded on Luciobarbus capito and Capoeta capoeta from the Caspian Sea basin in Iran and Turkey. Paradiplozoon bliccae , exhibiting a wide host range in the Middle East, expressed both morphological and genetic intraspecific variabilities. The four Paradiplozoon species collected in the Middle East were placed in divergent clades, showing the rich evolutionary history of diplozoid parasites in the Middle East. Our study also revealed that two lineages of African diplozoids have a Middle Eastern origin. We stress the importance of applying an integrative approach combining morphological, ecological and molecular methods to reveal the real diversity of diplozoids.

Background: Here we provide a comparative analysis of the genetic structure of populations (based on nad1 mtDNA) of Isthmiophora melis isolated from the American mink (Neogale vison), an introduced invasive species, commonly occurring in the territory of Poland, and from the striped field mouse (Apodemus agrarius)., Methods: A total of 133 specimens of I. melis were obtained from naturally infected N. vison collected from six localities in Poland (108 samples) and 25 individuals of I. melis from A. agrarius. All sequences of the nad1 gene obtained during the present study were assembled and aligned. The standard statistics for haplotype composition, i.e., the number of haplotypes, haplotype diversity, nucleotide diversity, and average number of nucleotide differences, were calculated. Haplotype analysis and visualization of haplotype frequency among populations were performed using a median-joining network., Results: Based on the samples collected from different localities in Poland, our study revealed that the overall genetic diversity of I. melis isolated from the American mink and of the striped field mouse do not differ significantly. The median-joining network showed that the three main haplotypes are in the centre of a star-like structure, with the remaining haplotypes as the satellites, reflecting the recent expansion of the populations., Conclusions: The overall genetic diversity of I. melis isolated from the American mink and striped field mouse reveals a high level of homogeneity. Moreover, regional differences in the food composition of the definitive hosts play an important role in shaping the genetic structure of the trematode populations., (© 2023. The Author(s).)

For parasites with complex multi-host life cycles, the facultative truncation of the cycle represents an adaptation to challenging conditions for transmission. However, why certain individuals are capable of abbreviating their life cycle while other conspecifics are not remains poorly understood. Here, we test whether conspecific trematodes that either follow the normal three-host life cycle or skip their final host by reproducing precociously (via progenesis) in an intermediate host differ in the composition of their microbiomes. Characterization of bacterial communities based on sequencing of the V4 hypervariable region of the 16S SSU rRNA gene revealed that the same bacterial taxa occur in both normal and progenetic individuals, independent of host identity and temporal variation. However, all bacterial phyla recorded in our study, and two-thirds of bacterial families, differed in abundance between the two morphs, with some achieving higher abundance in the normal morph and others in the progenetic morph. Although the evidence is purely correlative, our results reveal a weak association between microbiome differences and intraspecific plasticity in life cycle pathways. Advances in functional genomics and experimental microbiome manipulation will allow future tests of the significance of these findings.

We developed microsatellite markers to use in studying the population genetics of the trematode Alloglossidium renale, a fluke with a precocious life cycle where sexual maturation occurs in a grass shrimp. Among 21 tested loci in a Mississippi population sample, 14 were polymorphic, 12 of which significantly deviated from Hardy-Weinberg Equilibrium (HWE). We estimated identity disequilibrium (ID) to confirm whether the deviations from HWE were due to significant amounts of selfing or due to technical factors. The selfing rate derived from F IS was 86.6%, whereas the selfing rate obtained by ID was 83.9%, indicating that the deviation in HWE was due to a high amount of selfing within the population. These markers will be useful for ecological and evolutionary studies of A. renale especially in relation to the interplay of hermaphroditic mating systems, inbreeding depression, and transmission dynamics., Competing Interests: Declaration of Competing Interest none., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Three juvenile Atlantic tripletail Lobotes surinamensis caught opportunistically in Charleston Harbor (South Carolina, USA) and maintained in captivity for over three months displayed an altered swimming behavior. While no direct causation can be demonstrated herein, fish were infected in their brain by strigeid trematode larvae (metacercariae) of Cardiocephaloides medioconiger , which were identified via ITS2 and 28S ribosomal RNA gene sequencing . Histology showed nonencysted metacercariae within the brain ventricle between the optic tectum and tegmentum, causing distortion of tegmental parenchyma. Aggregates of mononuclear inflammatory cells were in the ventricle adjacent to metacercariae. Metacercarial infection by Cardiocephaloides medioconiger has been reported from the brain and eyes of only two other fish species from the northern US Atlantic coast: the grey mullet Mugil cephalus and silverside Menidia menidia, but this identification is problematic and needs molecular verification. Atlantic tripletail is a new report as a second intermediate host for C. medioconiger and South Carolina is a new locality. Cardiocephaloides species in general have a low host specificity and infection by C. medioconiger could propagate to other fishes and affect neighboring natural ecosystems., Competing Interests: The authors declare there are no competing interests., (©2023 de Buron et al.)

The identity of a larval bucephalid infecting the eastern oyster, Crassostrea virginica (Gmelin, 1791), from a tidal river in Virginia is investigated using ribosomal deoxyribonucleic acid (rDNA). The internal transcribed spacer (ITS1, 5.8S, ITS2) region and a portion of the 28S rDNA were isolated from genomic DNA from sporocysts containing cercariae and compared with sequences from GenBank and from our previous collections of possibly related bucephalids. The studied larval bucephalid was 100% identical at the ITS1, 5.8S, and partial 28S rDNA sequences with Prosorhynchoides paralichthydis (Corkum, 1961) Curran and Overstreet, 2009; however, it differed from P. paralichthydis by 6 bases plus 3 deletions in the ITS2 region. This level of variation at the ITS2 region has been demonstrated among some Indo-Pacific species of Prosorhynchoides Dollfus, 1929, suggesting that the larval bucephalid represents an unidentified or innominate species of Prosorhynchoides that is closely related to P. paralichthydis., (© American Society of Parasitologists 2023.)

While monogenean worms are mainly parasites of the gills and skin of fish, and to a lesser extent parasites of the oral cavity, urinary bladder, and/or conjunctival sacs of amphibians and freshwater turtles, Oculotrema hippopotamiStunkard, 1924 is the single monogenean polystome reported from a mammal, the common hippopotamus (Hippopotamus amphibius Linnaeus). Several hypotheses have been suggested in the last decade to explain the origin of this enigmatic parasite which infects the conjunctival sacs of H. amphibius. Based on a molecular phylogeny inferred from nuclear (28S and 18S) and mitochondrial (12S and COI) sequences of O. hippopotami and chelonian polystomes, we found a sister group relationship between O. hippopotami and Apaloneotrema moleri (Du Preez & Morrison, 2012). This result suggests lateral parasite transfer between freshwater turtles and hippopotamuses, thus likely reflecting one of the most exceptional known examples of host-switching in the course of vertebrate evolution. It also demonstrates that the proximity in the ecological habitat of parasites within host species is an important feature for their speciation and diversification. Because A. moleri and its host, the Florida softshell turtle (Apalone ferox (Schneider)), are restricted to the USA, we suggest that an ancestral stock of parasites may have been isolated on primitive African trionychids after they diverged from their American relatives, and then switched to hippopotamuses or anthracotheres in Africa., (Copyright © 2023 Australian Society for Parasitology. All rights reserved.)

Many parasites utilize asexual and sexual reproduction and multiple hosts to complete their life cycles. How these taxa avoid inbreeding is an essential question for understanding parasite evolution and ecology. Aquatic trematodes that require multiple host species may benefit from diverse genetic parasite assemblages accumulating within second intermediate hosts prior to sexual reproduction in definitive hosts. However, Cotylurus species are able to utilize the same snail species as first and second intermediate hosts, potentially resulting in the accumulation of genetically identical clones (clonemates) prior to sexual reproduction. In this study, we developed and analysed novel microsatellite loci to determine if clones are accumulating within snail hosts prior to ingestion by bird hosts and the effects this could have on parasite inbreeding. Contrary to previous studies of aquatic trematodes, significantly large numbers of clonemates were present within snails, but full-sibs were not. Genetic structure was present over a relatively small geographical scale despite the use of vagile definitive hosts. Phylogenetic analysis identified the Cotylurus sp. clones as belonging to a single species. Despite the presence of clones within snails, mating between clones/selfing was not common and heterozygosity is maintained within individuals. Potential issues with clones mating may be mitigated by the presence of snails with numerous clones, the consumption of many snails by bird hosts and parasite clone recognition/avoidance. Use of the same host species for multiple life stages may have advantages when parasites are able to avoid inbreeding and the required hosts are common., (© 2022 John Wiley & Sons Ltd.)

Pseudomurraytrema fergusoni n. sp. is described from the Pealip Redhorse, Moxostoma pisolabrum from the Black River (White River drainage), Lawrence County, Arkansas, USA. This represents the second monogenean described from M. pisolabrum as well as the second species of Pseudomurraytrema reported from an Arkansas catostomid. The description includes partial 18S rRNA and 28S rRNA gene sequences (732 bp and 851 bp, respectively), helping fill a void in sequence data from North American monogeneans, particularly those in the genus Pseudomurraytrema. In addition, histopathologic changes associated with the infection resulted in severe localized pathologic lesions in gills of the host, suggesting compromise of respiratory surfaces within affected areas adjacent to the worms., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

A new genus, Doorochen n. gen., is erected for four species of Postlepidapedon Zdzitowiecki, 1993, all of which inhabit members of the labroid genus Choerodon Bleeker, the tuskfishes, and which molecular phylogenies have indicated are not congeneric with the type-species, P. opisthobifurcatum (Zdzitowiecki, 1990) Zdzitowiecki, 1993. Doorochen secundum (Durio & Manter, 1968) n. comb. from Choerodon graphicus (De Vis), the Graphic tuskfish, from the Great Barrier Reef (GBR) and New Caledonia is designated the type-species of the new genus. Other species recognised are Doorochen spissum (Bray, Cribb & Barker, 1997) n. comb. from C. venustus (De Vis), the Venus tuskfish, C. cyanodus (Richardson), the Blue tuskfish, and C. graphicus from the GBR; D. uberis (Bray, Cribb & Barker, 1997) n. comb. from C. schoenleinii (Valenciennes), the Blackspot tuskfish, and C. venustus from the GBR and Moreton Bay; and D. philippinense (Machida, 2004) n. comb. from C. anchorago (Bloch), the Orange-dotted tuskfish, from Philippine waters. In addition to these four species, two new species are described: D. zdzitowieckii n. sp. from C. fasciatus (Günther), the Harlequin tuskfish, and C. graphicus from the GBR; and D. goorchana n. sp. from C. anchorago from the GBR and Palau. The genus Postlepidapedon is now considered to comprise just two species, P. opisthobifurcatum and P. quintum Bray & Cribb, 2001. The relationships of Doorochen, Postlepidapedon, Myzoxenus Manter, 1934 and Intusatrium Durio & Manter, 1968 in the family Lepidapedidae Yamaguti, 1958 are discussed., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Muscle gross lesions, associated to parasites, were routinely found during self-inspection in a Spanish fish plant processing Atlantic swordfish. To determine the taxonomic status of these parasites, molecular analysis was performed based on 18S, ITS1, 5.8S, ITS2 and 28S rDNA sequences, obtaining a consensus sequences of 4581 bp for the cestode and 4200 bp for the trematode. Taxonomic affiliation was determined by phylogenetic analysis of combined SSU + LSU rDNA regions using maximum likelihood models. Molecular characterization allows us to identify the trematode Maccallumtrema xiphiados and the cestode Molicola sp. infecting the musculature of the Atlantic swordfish. Both parasites are responsible of significant economic loss to fish industry due to commercial rejection of parasitized products., 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 © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

The anomaly P is a mass morphological anomaly found in some populations of anuran amphibians (water frogs of the genus Pelophylax and toads of the genera Bufo and Bufotes) caused by the parasitic flatworm Strigea robusta. Minimum dose of cercariae for the appearance of the anomaly P remains unknown. However, it is important information for understanding of host population dynamics after invasion and the effects of the parasite on the second intermediate hosts. Herein, the invasion properties of S. robusta in Pelophylax lessonae tadpoles (Anura: Ranidae) and minimum dose for appearance of mild and severe forms of the anomaly P syndrome were described after direct experiments with certain numbers of cercariae exposure. Experimental groups of tadpoles have been exposed to eight doses of cercariae (2, 4, 6, 8, 10, 12, 14 and 16). A total of 63.8% tadpoles survived to the end of this experiment. It was revealed that a mild form of the anomaly P (polydactyly) can appear after infection by two cercariae, while the severe form traits appear after infection by four cercariae. The mean number of detected encysted metacercariae was reached to 53.5%. Differences in infection rates can be explained by the presence of an individual immune response in tadpoles or by the presence of different genetic lineages of the parasite infecting the same snail, which have different infectious potential. Low doses of infection leading to the induction of anomalies characterize S. robusta as a highly pathogenic species for amphibian species that are susceptible to infection and show an abnormal phenotype., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

A new digenean species belonging in EncyclobrephusSinha, 1949 is described, and the generic diagnosis is amended to accommodate variation in several features of the new species. Worms were collected from the intestines of 2 specimens of the Mekong snail-eating turtle, Malayemys subtrijuga (Schlegel and Müller, 1845). Permanent whole-mounted worms were studied using light microscopy, and ribosomal DNA (rDNA) sequences were generated from 3 worms. We investigated the phylogenetic relationship of the new species among some digenea using separate Bayesian inference analyses, 1 based on the 28S rDNA gene and rooted using a species from the Monorchioidea Odhner, 1911, and a second based on the internal transcribed spacer 1 region rooted by a species in the Microphalloidea Ward, 1901. Prior to the analyses, Encyclobrephus was classified in the Encyclometridae Mehra, 1931. Previous studies using rDNA from the type species for the family, Encyclometra colubrimurorum (Rudolphi, 1819) Baylis and Cannon, 1924, have demonstrated that En. colubrimurorum is closely related to species of Polylekithum Arnold, 1934 in the Gorgoderoidea Looss, 1901. Nevertheless, phylograms from both analyses indicated that the new species of Encyclobrephus belongs in the Plagiorchioidea Lühe, 1901, related to species in the families Cephalogonimidae Looss, 1899, Plagiorchiidae Lühe, 1901, Reniferidae Pratt, 1902, and Telorchiidae Looss, 1899. The present results suggest that Encyclobrephus is not closely related to En. colubrimurorum. Familial classification of Encyclobrephus is contingent on molecular data availability for the type species but it should be removed from the Encyclometridae and classified as incertae sedis within the Plagiorchioidea. Encyclometridae belongs in the Gorgoderoidea, not the Plagiorchioidea., (© American Society of Parasitologists 2023.)

We herein resurrect and emend PlesiocreadiumWinfield, 1929 (Digenea: Macroderoididae) and provide a supplemental description of its type species, Plesiocreadium typicumWinfield, 1929, based on adult specimens collected from the intestine of bowfins, Amia calva Linnaeus, 1766 (Amiiformes: Amiidae), captured in the L'Anguille River (Mississippi River Basin, Arkansas), Big Lake (Pascagoula River Basin, Mississippi), Chittenango Creek (Oneida Lake, New York), and Reelfoot Lake (Tennessee River Basin, Tennessee). Plesiocreadium spp. (Pl. typicum and Plesiocreadium flavum [Van Cleave and Mueller, 1932] n. comb.) differ from other macroderoidids by having a dorsoventrally flat forebody, ceca that extend posteriad beyond the testes and that do not form a cyclocoel, testes that are greater than one-half of maximum body width, a cirrus sac that is dorsal to the ventral sucker and arches dextrad or sinistrad, a uterine seminal receptacle, asymmetrical vitelline fields that remain separated anteriorly and posteriorly and that extend anteriad to the level of the ventral sucker, and an I-shaped excretory vesicle. Bayesian phylogenetic analyses (ITS2 and 28S) recovered monophyletic Plesiocreadium sensu stricto (as defined herein) sister to Macroderoides trilobatusTaylor, 1978 and that clade sister to the remaining macroderoidids, with sequences ascribed to species of Macroderoides Pearse, 1924 recovered as paraphyletic. We regard Macroderoides parvus (Hunter, 1932) Van Cleave and Mueller, 1934, M. trilobatus, and RauschiellaBabero, 1951 as incertae sedis. Arkansas, New York, and Tennessee comprise new locality records for Pl. typicum., (© American Society of Parasitologists 2023.)

Background: Unresolved taxonomic classification and paraphyly pervade the flatworm class Monogenea: the class itself may be paraphyletic and split into Polyopisthocotylea and Monopisthocotylea; there are some indications that the monopisthocotylean order Dactylogyridea may also be paraphyletic; single-gene markers and some morphological traits indicate that the family Ancyrocephalidae is paraphyletic and intertwined with the family Dactylogyridae., Methods: To attempt to study the relationships of Ancyrocephalidae and Monopisthocotylea using a phylogenetic marker with high resolution, we sequenced mitochondrial genomes of two fish ectoparasites from the family Dactylogyridae: Dactylogyrus simplex and Dactylogyrus tuba. We conducted phylogenetic analyses using three datasets and three methods. Datasets were ITS1 (nuclear) and nucleotide and amino acid sequences of almost complete mitogenomes of almost all available Monopisthocotylea mitogenomes. Methods were maximum likelihood (IQ-TREE), Bayesian inference (MrBayes) and CAT-GTR (PhyloBayes)., Results: Both mitogenomes exhibited the ancestral gene order for Neodermata, and both were compact, with few and small intergenic regions and many and large overlaps. Gene sequences were remarkably divergent for nominally congeneric species, with only trnI exhibiting an identity value > 80%. Both mitogenomes had exceptionally low A + T base content and AT skews. We found evidence of pervasive compositional heterogeneity in the dataset and indications that base composition biases cause phylogenetic artefacts. All six mitogenomic analyses produced unique topologies, but all nine analyses produced topologies that rendered Ancyrocephalidae deeply paraphyletic. Mitogenomic data consistently resolved the order Capsalidea as nested within the Dactylogyridea., Conclusions: The analyses indicate that taxonomic revisions are needed for multiple Polyopisthocotylea lineages, from genera to orders. In combination with previous findings, these results offer conclusive evidence that Ancyrocephalidae is a paraphyletic taxon. The most parsimonious solution to resolve this is to create a catch-all Dactylogyridae sensu lato clade comprising the current Ancyrocephalidae, Ancylodiscoididae, Pseudodactylogyridae and Dactylogyridae families, but the revision needs to be confirmed by another marker with a sufficient resolution., (© 2023. The Author(s).)

Echinoparyphium aconiatum (Digenea: Echinostomatidae) is an intestinal parasite of anatid and snail-eating birds. In Eurasia, it is also common in lymnaeid snails, which may serve as the first and second intermediate hosts. The systematics of its genus, Echinoparyphium, have long been inadequate, with poor descriptions and extensive synonymy. To provide a basis for developing new genetic markers for studies of the identification and systematics of echinostomatids, the complete Ep. aconiatum mitogenome is described and compared with other digeneans. The circular mt molecule of this species is 14,865 bp in length, with an average A + T content of 64.33%. It contains 12 protein-coding genes and 22 transfer RNA genes. The 3' end of nad4L overlaps the 5' end of nad4 by 40 bp, while the atp8 gene is absent. Twenty-one transfer RNA genes transcribe products with conventional cloverleaf structures, while one transfer RNA gene has unpaired D-arms. Comparative analyses indicate that Echinoparyphium aconiatum is closely related to Echinochasmus japonicus and Echinostoma miyagawai. The phylogenetic results, using our mitochondrial data indicated Ep. aconiatum as a sister taxon of Hypoderaeum conoideum in a monophyletic clade. Our data and analyses serve as the first representative sequenced mt genome from genus Echinoparpyhium, providing additional markers to clarify the taxonomic position of Ep. aconiatum., Competing Interests: Declaration of Competing Interest The authors declare that no conflict of interest exists., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Polystomatid flatworms of amphibians are represented in the Neotropical realm by species of Mesopolystoma, Nanopolystoma, Parapseudopolystoma, Polystoma, Riojatrema and Wetapolystoma but only species of Polystoma are known from Brazil, namely Polystoma cuvieri, P. knoffi, P. lopezromani and P. travassosi. During a survey of monogeneans infecting amphibians in the north-eastern region of Pará State, the Cayenne Caecilian Typhlonectes compressicauda was found to be infected with Nanopolystoma tinsleyi and the Veined Tree Frog Trachycephalus typhonius was found to harbor Polystoma lopezromani. A yet unknown species of Polystoma was also encountered in the urinary bladder of the Steindachner's Dwarf Frog, Physalaemus ephippifer. This new species, which is the second species reported from Physalaemus spp., is described herein as Polystoma goeldii n. sp. and its life cycle is also illustrated. The new species can be distinguished from Polystoma spp. from other neotropical realm by a combination of characteristics, including hamuli morphology, outer/inner hamuli length ratio, haptor/total body length ratio, genital bulb/total body length ratio, genital spine number and COI molecular characters., (Copyright © 2022. Published by Elsevier B.V.)

Host-parasite coevolution is one of the fundamentals of evolutionary biology. Due to the intertwined evolutionary history of two interacting species and reciprocal coadaptation processes of hosts and parasites, we can expect that studying parasites will shed more light onto the evolutionary processes of their hosts. Monogenea (ectoparasitic Platyhelminthes) and their cyprinoid fish hosts represent one of the best models for studying host-parasite evolutionary relationships using a cophylogenetic approach. These parasites have developed remarkably high host specificity, where each host species often serves as a potential host for its own host-specific monogenean species. Here, the cophylogenetic relationships in the Dactylogyrus-Squalius system was investigated, as Squalius is one of several cyprinoid genera with puzzling phylogeography and inhabits all four major peri-Mediterranean peninsulas. Of 29 endemic Squalius species examined for the presence of Dactylogyrus parasites, a total of 13 Dactylogyrus species were collected from the gills of 20 Squalius species across a wide range of distribution. Phylogenetic reconstruction revealed a polyphyletic origin for Dactylogyrus species parasitizing congeneric Squalius, with four major clades being recognized. On the basis of the delimitation of host specificity, strict specialists parasitizing single host species, geographic specialists parasitizing congeners in a limited geographical region, and true generalists parasitizing congeners in various geographical regions were recognized in Dactylogyrus species parasitizing Squalius. The phylogenetic reconstruction of Squalius hosts revealed two major clades, the first encompassing only peri-Mediterranean species and the second including species from other Euro-Asian regions. Distance-based cophylogenetic methods did not reveal a statistically significant global cophylogenetic structure in the studied system; however, several host-parasite links among Iberian endemic species contributed significantly to the overall structure. The widest host range and associated genetic variability were recorded for D. folkmanovae, parasitizing nine Squalius species, and D. vistulae, parasitizing 13 Squalius species. Two different dispersion mechanisms and morphological adaptations to Squalius hosts were clearly reflected in the contrasting cophylogenetic patterns for these two species with different levels of host specificity. While host-parasite cospeciation plays an important role in diversification within D. folkmanovae, diversification within D. vistulae is driven mainly by host switching., 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 © 2022 Elsevier Inc. All rights reserved.)

During the parasitological examination of molluscs Abra segmentum obtained from the Black Sea basin, parthenitae belonging to the family Faustulidae were found. The cercariae were obtained by natural emergence and were studied using differential interference contrast microscopy and scanning electron microscopy. Specimens resemble Cercaria pennata ex Tapes rugatus which was described from the Sevastopol area, in the shape and length of the body, tail length, location and shape of internal organs, suckers, pharynx, testicular rudiments, and the number and position of longitudinal lamellae on the tail finlets. To date, there are only limited descriptions of the parthenitae of C. pennata without detailed measurements, thus the taxonomic position of the individuals studied needs thorough revision and molecular verification. According to the molecular analyses, C. pennata was identical to that of published sequences of Pronoprymna ventricosa .