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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.)

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

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).)

The humpback whale (Megaptera novaeangliae) is a cosmopolitan migratory, seasonal mysticete that frequents the Brazilian coast. Strands of specimens may occur during the migratory stay in the country. In 2021 and 2022, three live humpback whales stranded on the coast of Rio Grande do Sul and Santa Catarina states in southern Brazil. After euthanasia, specimens were necropsied, and organs were thoroughly examined for lesions. Grossly, in all three cases, the liver exhibited multifocal, irregular, firm, white areas on the hepatic capsule, which extended into the parenchyma. On the cut surface, the livers were yellow to pale brown with orangish to greenish areas, the bile ducts were prominent, thickened, and severely dilated, and leaf-shaped flukes were found inside of them. Additionally, one case showed moderate atrophy of the right hepatic lobe. The histological findings included dilation of bile ducts, hyperplasia of the bile duct epithelium, marked inflammatory infiltration of lymphocytes, plasma cells, and eosinophils, and portal fibrosis. The parasite Brachycladium goliath was both morphologically and molecularly identified based on diagnostic key for trematodes and the original description of the species, and the amplification and sequencing of the ITS-2 region, respectively. Even though hepatic injury was not the primary cause of stranding, it may have contributed to the debilitation of the whales. To the authors' knowledge, this is the first study that reports M. novaeangliae as a definitive host of B. goliath and that describes the lesions caused by the parasite in cetaceans., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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.)

The genus Clinostomum has been recently a subject of a large number of molecular phylogenetic studies that have uncovered a larger species diversity than we thought. In Argentina, only two nominal species have been reported, namely C. detruncatum and C. marginatum. Three putative species represented by metacercariae were recently molecularly diagnosed, and there are at least two additional metacercarial morphotypes diagnosed on morphological grounds. Here, we molecularly characterized specimens of Clinostomum sampled from freshwater fishes and fish-eating birds from Argentina through mtDNA cytochrome c oxidase subunit I (COI). Unexpectedly, the phylogenetic analysis uncovered three new additional genetic lineages, two of them corresponding to metacercarial stages and another matching COI sequences of C. heluans Braun, 1899, being considered conspecific, whereas the others still require formal description. Additionally, we add a new host species for a lineage molecularly diagnosed in a previous study. The adult specimens recovered from A. cocoi in Buenos Aires Province represented a new species clearly distinguished from the two species previously reported in Argentina. Clinostomum detruncatum is distinguished from the new species by possessing a characteristic tenoidean uterus, and testes located more posteriorly. Clinostomum marginatum is morphologically similar but differs from the new species in having rounded ovary, posterior testis lobated, and lateral cirrus-sac and displacing the anterior testis, and vitelline follicles not extending beyond the caeca end. Our study raises the number of Clinostomum species in Argentina up to 10. We describe the new species herein., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

A new species of Crassicutis Manter, 1936 (Digenea: Megaperidae) is described from the intestine of Satanoperca jurupari (Cichlidae) in the Amazon River basin, Brazil. The genus Crassicutis currently contains eight species. Crassicutis manteri n. sp. is morphologically very similar to Crassicutis cichlasomae Manter, 1936, a parasite of cichlids reported from Mexico, the Antilles, and Central and South America. Molecular data revealed that C. cichlasomae represents a species complex in Middle American cichlids. The new species can be readily distinguished from C. cichlasomae sensu lato, and the other congeners, by a combination of morphological traits such as a narrow, elongate mouth opening (versus spherical in other species), the tandem position of testes (symmetrical or oblique in most congeners), narrow body widening towards its posterior end (versus widely oval, leaf-like in other species), and short intestinal caeca ending close to the posterior end of the posterior testis (versus reaching more posteriorly in other species). Six novel sequences of 28S rDNA, ITS1, and cox1 were generated for two isolates of the new species. Sequences of the 28S rRNA gene were used to corroborate that Crassicutis is sister taxa of Homalometron Stafford, 1904. Mitochondrial DNA corroborated the distinction of the new species with previously sequenced congeners in Middle American cichlids; the interspecific divergence between the new species and the genetic lineages of C. cichlasomae was very high, varying between 23.7 and 27.2%. Biogeographical implications of our findings are briefly discussed including questionable validity of records of C. cichlasomae from South America.

Many Pauciconfibula spp. have a long and complicated taxonomic history. The remaining unsolved taxonomic confusion in this genus is impelled by the host range and status of Pauciconfibula spp. from trachinid fishes: Pauciconfibula trachini and Pauciconfibula draconis, from Trachinus radiatus and Trachinus draco (Trachinidae), respectively. Pauciconfibula trachini was reported on Trachinus draco, type host of Pauciconfibula draconis suggesting thus a stenoxenic specificity for the former monogenean and the occurrence of two congeneric polyopisthocotyleans on a single host. Moreover, the validity of Pauciconfibula draconis was repeatedly questioned by several authors, unjustified synonymy between the two species was proposed, and the delimitations between the two species remained unsolved. Original descriptions were also incomplete and poorly illustrated. In this study, we provide a detailed illustrated redescription of both species based on newly collected specimens of Pauciconfibula trachini and Pauciconfibula draconis collected from their type hosts from off three Mediterranean localities: Algeria, Tunisia, and Italy. Integrative taxonomy using COI sequences was applied to resolve the delimitation between Pauciconfibula trachini and P. draconis. This study provides the first DNA barcoding for members of this genus.

A new hemiuroidean species, Genarchella pichileufuensis n. sp. (Derogenidae: Halipeginae), was found in the stomach of the siluriform freshwater fish, Hatcheria macraei (Girard, 1855), in the Pichileufu River, Patagonia, Argentina. Its rediae with immature cystophorous cercariae were found in the snail Heleobia hatcheri (Pilsbry, 1911) in the same site. The present new species is morphologically featured by having a cyclocoel in the hindbody unlike the other species of the genus. The characteristics of this species allowed us to amend the diagnosis of the genus Genarchella as follows: cyclocoel present or absent; testes symmetrical to tandem; ootype pouch present. In the phylogenetic analysis, G. pichileufuensis forms a well-supported clade with Genarchella spp. recovered from Mexican freshwater fishes. This clade is included in the cluster of representatives of the subfamily Halipeginae. So far, three hemiuroidean species, Thometrema patagonica (Szidat, 1956), Derogenes lacustris Tsuchida, Flores, Viozzi, Rauque et Urabe, 2021 and G. pichileufuensis n. sp., have been reported from freshwater fishes in Argentinean Patagonia.

The parasite genus Notocotylus comprises at least 50 species colonizing mainly aquatic birds and to a lesser extent some mammals, particularly rodents. Here trematode specimens isolated from a wild black swan were characterized and identified to belong to the genus Notocotylus via morphological and molecular analyses. Phylogenetic position of the isolate among other trematodes was determined based on the ribosomal internal transcribed spacer (ITS) 1 and 2. The complete mitochondrial (mt) genome of the isolate was amplified, sequenced, assembled, analyzed, and annotated. The isolate has an AT-rich mt genome (14,317 bp in length) that comprises 12 protein-coding genes (PCGs), 22 transfer RNA genes, and two ribosomal RNA genes. The Notocotylus isolate identified in this study has relatively high mt genome sequence identity and identical gene content and arrangement to a known Notocotylidae species, Ogmocotyle sikae. The isolate formed a genetic clade with O. sikae in phylogenetic analysis of the concatenated PCG amino acid sequences. Compared to the ITS, the trematode mt genome appears more informative for resolving high-level phylogenies. To the best of our knowledge, this is the first study exploring the complete mt genome for the genus Notocotylus, and it offers a novel genomic resource that has important implications for trematode phylogenetics.

We describe the alloglossiid trematode Magnivitellinum saltaensis n. sp., a parasite of the characiform fish Psalidodon endy, and its life cycle from Salta, northwest of Argentina. This is the first life cycle described for a species belonging to the genus Magnivitellinum. Cercariae emerged naturally from Biomphalaria tenagophila snails and infected experimentally exposed larvae of Diptera and Ephemeroptera as second intermediate hosts. These larvae in turn were exposed to commercially raised fish, and adults were recovered from characiform albino fish Gymnocorymbus ternetzi. Molecular analysis of natural and experimental adults showed the same genetic sequence for the partial region of 28S rDNA, thus confirming conspecificity. Comparison of these sequences with those published for M. simplex from Mexico showed 1.45% divergence, indicating that the specimens found in Salta belong to a different species, the third described of Magnivitellinum, in agreement with morphological data, geographical location, and host species composition. The new species is distinguished by its small body, vitelline follicles extending from the mid-level of the ventral sucker, Y-shaped excretory vesicle, and presence of papillae around the mouth.

The global invasive anguillid gill parasite Pseudodactylogyrus anguillae (Yin and Sproston, 1948) has only recently been documented from eels in South Africa. As there is no known eel trade in South Africa, the source of introduction of this parasite has been debated, and its status as an alien parasite was rendered uncertain. We report on the first infection of Pseudodactylogyrus anguillae from the giant mottled eel Anguilla marmorata from the Phongolo River (South Africa) using classic morphological and molecular methodologies and clarify the introduction status category of this parasite as alien and invasive.

Renicolid digeneans are frequently observed in the renal tubules and ureters of seabirds, such Puffinus puffinus, a migratory species distributed along the Brazilian coast. However, few studies have focused on the relationship between renicolid infection and health status in P. puffinus. Thus, the aim of this study was to describe (i) renal and systemic alterations, (ii) the renicolids and (iii) the biological aspects associated with the presence of renicolids in P. puffinus. Gross and histological assays were performed in 93 P. puffinus stranded on the Paraná coast, southern Brazil, and renicolids were submitted to morphological and molecular assays. A high prevalence of renicolids in P. puffinus (71/93) was observed. In the kidney, the main microscopic findings were lymphocytic interstitial infiltrate, ductal ectasia and tubular necrosis. The renal lesions were significantly associated with the parasite infection. The morphological (n = 84) and molecular analyses (n = 2) confirmed the species as Renicola sloanei (100% and 95.9% of nucleotide identity with R. sloanei strains from P. puffinus and from Spheniscus demersus, respectively). In both parasitized and non-parasitized animals, cardiac and skeletal muscle degeneration and necrosis were the most frequent systemic changes. Therefore, the results suggest renicolids being a possible cause for the demonstrated renal alterations. A contribution of this parasite to a decreased health status of Puffinus puffinus along their migratory route is possible.

The present study represents the first detailed description of the haptoral sclerites of Macrogyrodactylus clarii Gussev 1961. Light microscopy reveals outgrowths of the hamuli roots; two lateral spine-like extensions of the hood-like accessory sclerites; a ridged, fan-shaped distal end of an accessory sclerite; and two thread-like accessory sclerites with biforked ends associated with the pointed hooked region of each hamulus. Transmission electron microscopy (TEM) reveals the presence of parallel tubules in the root of the hamuli and structural differences along the length of the hamulus including the root, shaft, and pointed hooked region. The root consists of two layers, the shaft four layers and pointed hooked region only one layer with dense outer serrations. Characteristic features of the hamulus root are the presence of longitudinally orientated parallel tubules in its central core and parallel electron-dense ridges in the outer layer of its middle region; features not observed in either the shaft or the pointed hooked region. Each hamulus blade of M. clarii is associated with haptoral gland cells producing electron-dense secretory bodies. The 16 marginal hooklets each consist of a blade (sickle) articulating with a handle at the guard region and a domus. TEM revealed structural differences between the handle, the blade at the articulation region, and the distal hooked region. The domus, a filamentous thread-like sclerite at the light microscope level, consists of two electron-dense, fibrous thickenings connected to each other by a cytoplasmic process. Each marginal hooklet is associated with a small cavity and a large reservoir of homogeneous particles and secretory bodies. The possible functions of these structures are discussed in relation to equivalent features in other monogeneans.

Diplostomum ardeae Dubois, 1969 has seldom been reported since its description from the great blue heron (Ardea herodias L., 1758) in the USA. Sequences obtained in this study from the barcode region of cytochrome c oxidase 1 (CO1) in diplostomids from black-crowned night heron (Nycticorax nycticorax (L., 1758)) in Puerto Rico matched data from D. ardeae from A. herodias in the type region. We also obtained DNA barcodes from morphologically similar diplostomids from a rufescent tiger heron (Tigrisoma lineatum (Boddaert, 1783)) and from metacercariae from eye lenses of Trachelyopterus galeatus (Linnaeus, 1766) from the Paraná River basin in Argentina and Brazil, respectively. Barcodes matched (97-100% identity) in these South American adult and larval specimens as well as in recently published sequences from metacercariae from 11 other siluriform fishes from the same region. Barcodes from the South American species, which we describe as Diplostomum lunaschiae n. sp., differed from those of D. ardeae by 7.2-9.8%, and the new species differs from D. ardeae in its size, pharynx:oral sucker length ratio, egg:body length ratio, and distribution of vitellaria. As in prior phylogenetic analysis of CO1 sequences, both D. ardeae and D. lunaschiae n. sp. were not associated with Diplostomum. In more character-rich analyses of nuclear rDNA and of mitochondrial genomes, D. ardeae was an early divergent member of clades of species of Diplostomum. Consequently, we continue to consider D. ardeae and D. lunaschiae n. sp. members of Diplostomum, in contrast to recent suggestions that these species may belong to a different genus.

Black bullhead Ameiurus melas (Actinopterygii: Siluriformes) is an alien fish species of North American origin, which has expanded its invasive geographical range in Europe. In 2017-2019, 32 black bullhead specimens from the Lake Srebarna Biosphere Reserve, Bulgaria, were examined for monogenean parasites. Two species of monogeneans were recorded and identified on the basis of morphological and molecular data: Ligictaluridus pricei (Ancyrocephalidae), with prevalence 100% and intensity 2-32 (mean 13.3 ± 6.8), and Gyrodactylus nebulosus (Gyrodactylidae), with prevalence 72.0% and intensity 1-15 (mean 7.4 ± 4.3). Partial 18S rDNA and the ITS1 region of L. pricei were sequenced. For G. nebulosus, sequenced genes included the partial 18S rDNA and the entire ITS1-5.8S rDNA-ITS2 region as well as the mitochondrial COI gene. Both recorded monogenean species are specific parasites of North American ictalurid fishes and alien to Europe. The present study is the first record of L. pricei from Bulgaria and the first record of G. nebulosus from Europe and the Palaearctic Region.

A new species of microphallid trematode was collected from the intestine of the yellow-crowned night heron Nyctanassa violacea (L.) (Pelecaniformes: Ardeidae) from Veracruz, Mexico. Maritrema kostadinovae n. sp. differs distinctly from other members of Maritrema Nicoll, 1907 from the Americas by its smaller body size (262-435 × 242-363 μm), the extension of caeca (reaching to anterior level of ventral sucker), the size and shape of the cirrus (short, tubular and unarmed) and metraterm (simple and thin-walled), the position of the genital pore (sinistrolateral to ventral sucker) and the arrangement of the vitellaria (horseshoe-shaped with posteriorly directed opening). Maximum likelihood and Bayesian inference analyses, based on partial 28S rDNA sequences, depicted M. kostadinovae n. sp. within the genus Maritrema with strong support. The new species is in a sister position to other available members of Maritrema, except for M. subdolum Jägerskiöld, 1909 that branches as the early divergent species in the Maritrema clade. The new species is the third species of Maritrema described from birds in Mexico. Comparative morphometric data for Maritrema taxa from birds and mammals from the Americas is provided.

In this study, we followed an integrative taxonomy approach to describe two new species of Gyrodactylus von Nordmann, 1832, and to identify specimens of G. breviradix Vega, Razzolini, Arbetman, and Viozzi, 2019, all three collected from ten spotted live-bearer Cnesterodon decemmaculatus (Jenyns, 1842), an endemic and widespread poeciliid from the Pampean region, which is the southernmost occurring species of the Poeciliidae in the Americas. Gyrodactylids were first characterized morphologically and mophometrically, and when possible, sequences of the Internal Transcribed Spacers (ITS1-5.8S-ITS2) and the cytochrome oxidase II (COII) were used to delimit species. Gyrodactylus breviradix, Gyrodactylus marplatensis n. sp., and Gyrodactylus pampeanus n. sp. were found on the fins and body surface of C. decemmaculatus in La Tapera Creek, Mar del Plata, Buenos Aires province, Argentina. A phylogenetic analysis combining newly generated sequences of one of the new species, G. marplatensis n. sp., and of G. breviradix, along with those available in GenBank for a further 36 species of Gyrodactylus, revealed that G. marplatensis n. sp. is a sister taxon of Gyrodactylus decemmaculati Vega, Razzolini, Arbetman, and Viozzi, 2019. Genetic distances for the ITS and COII gene were estimated among Gyrodactylus spp. and further supported the validity of the new species. Overall, morphometric and molecular data coincided in delimiting the new taxa, thus demonstrating the value of integrative taxonomy for the erection of new species of Gyrodactylus and species identification.

In the Afrotropic region, the genus Clinostomum is represented by four accepted and four unnamed species distinguished using molecular data. Here, we describe one of the four unnamed species as Clinostomum ukolii n. sp. based on metacercariae from siluriform fishes (Synodontis batensoda, Schilbe intermedius) collected in Nigeria and South Africa. The new species is distinguished by molecular data (39 new sequences of partial cytochrome c oxidase I ≥ 6.7% divergent from those of other species) and morphological differences from named and unnamed species in the same region. Metacercariae of C. ukolii n. sp. can be distinguished based on size, tegumental spines, and various aspects of the genital complex, including its position, lobation of the anterior testis, and the disposition and shape of the cirrus pouch. Although descriptions of new species of digeneans are typically based on the morphology of adults, we argue that in cases where data are available from metacercariae from regionally known species, new species can be described based on metacercariae, particularly when supported by molecular data, as here. Moreover, sub-adult reproductive structures can be clearly visualized in metacercaria of Clinostomum. Considering metacercariae as potential types for new species could advance clinostome systematics more rapidly, because metacercariae are encountered much more often than adults in avian definitive hosts.

Gyrodactylus nebulosus Kritsky and Mizelle, 1968 is reported for the first time from brown bullhead Ameiurus nebulosus (Siluriformes; Ictaluridae) in Nova Scotia. The study results from a screening of parasites with the potential to disrupt commercial rearing of wild-caught young-of-the-year (YOY) brown bullhead. Infected YOY were collected July 30, 2018 and estimated to be 3 weeks old. Eight of 10 fish were infected. Mean intensity was 3.1 ± 3.5 with a range of 1-10. The parasite occurred all over the body surface, but particularly on the ventral regions of the head including the base of the maxillary barbels. Diagnostically important features of the anchors, ventral bar/shield, marginal hooks, and male copulatory organ are described. A partial sequence of the 18S rRNA gene (432 bp) is included and represents the first confirmed molecular data for this species. Molecular analysis revealed a high similarity (99.3%) to a Gyrodactylus sp. reported from the same host, A. nebulosus, in Ontario and the next closest similarity (96.9%) to Gyrodactylus fairporti Van Cleave, 1921 from Ameiurus melas in Wisconsin. The report extends the known distribution of G. nebulosus from North Dakota, Iowa, and Ontario to Nova Scotia. The study concludes that any commercial venture to harvest local YOY brown bullhead from the wild for intense grow-out in captivity should include appropriate quarantine and therapeutic treatments for G. nebulosus as part of the operation.

We describe a new species, Gyrodactylus ginestrae n. sp., a parasite of the big-scale sand smelt (Atherina boyeri) from the Black Sea. This is the third monogenean species known from this fish host, found at 70% prevalence, but at relatively low abundance (1.9), on fish gills and fins. The new species is, both morphologically and genetically, most similar to G. salinae, which parasitizes the killifish Aphanius fasciatus (Cyprinodontidae) in the Mediterranean region. These species differ in the size of the haptoral hard parts and the number of small spines of the male copulatory organ. For molecular characterization, the internal transcribed spacer 1 (ITS1), 5.8S rRNA gene, and the internal transcribed spacer 2 (ITS2) were sequenced, completed by a fragment of the COII gene, thereby representing the first molecularly characterized gyrodactylid species from the Black Sea. Phylogenetic reconstruction based on the ITS1-5.8S-ITS2 sequence data indicated the position of G. ginestrae n. sp. in the marine "rugiensis" group of G. (Paranephrotus) and G. (Neonephrotus) subgenera which is part of the monophyletic "long ITS1" group. Taking into account the similarity of G. ginestrae n. sp. to several monogeneans from the Atlantic and Mediterranean regions, we suggest the Boreal-Atlantic origin of this species.

Metacercariae of Clinostomum Leidy, 1856 are frequently encountered in freshwater fish. In 2015, a provisional species of Clinostomum in People's Republic of China (PRC) was distinguished from C. complanatum (Rudolphi, 1819) in Europe based on divergent cytochrome c oxidase I (CO1). However, in subsequent studies in East Asia, the same divergent CO1 genotype was identified as C. complanatum. These matching sequences suggest that either the provisional East Asian species was incorrectly distinguished from C. complanatum in 2015 or that C. complanatum in East Asia was misidentified in later studies. We tested these alternatives by sequencing the mitochondrial genome of C. complanatum in Italy, which was 5.7% divergent from a previously published sequence from Clinostomum in PRC, including differences in 80 of 3390 (2.4%) translated amino acids. Partial CO1 sequences of specimens from PRC and those from Italy, Romania, and Turkey also each formed reciprocally monophyletic clades. Partial CO1 from the East Asian clade varied by mean 3.6% (range 2.4-4.8%) from C. complanatum from Italy, Romania, and Turkey; mean intra-clade CO1 variation was 0.3% (range 0-1.9%). Metacercariae from Europe and East Asia display significant morphometric variation, and data from the literature suggest morphological differences in the genital complex of adults. Although sequences of nuclear rDNA did not differ between isolates from the west and East Asia, taken together, these results lead us to describe a new species of Clinostomum.

The monogenean Microcotyle erythrini is atypical because it has been recorded from several fish host species in the Mediterranean Sea and Atlantic Ocean, in contrast to many species which are considered strictly specific. This could indicate a true lack of specificity or that several cryptic species are involved. This paper is a partial attempt to solve this problem. Specimens of a monogenean resembling M. erythrini were collected from bogues, Boops boops, caught off Algeria. A comparison with published descriptions and with museum specimens of M. erythrini did not yield any clear morphological difference. However, sequences of cytochrome c oxidase subunit I (COI) differed by 16.3% from that of M. erythrini (from GenBank, material collected from the type-host Pagellus erythrinus), indicating that the species was different. The species from B. boops is therefore described here as Microcotyle isyebi n. sp. and differential diagnoses with Microcotyle species from the Mediterranean and from sparids are provided. These results suggest that a molecular re-evaluation of other M. erythrini-like specimens from various fish hosts could reveal the existence of additional parasite biodiversity.

The development of metacercariae of Diplostomum pseudospathaceum Niewiadomska, 1984 is accompanied by profound morphological transformations often characterized as metamorphosis, which makes these metacercariae an interesting case for studying the morphogenesis of the digenean nervous system. Although the nervous system of D. pseudospathaceum is one of the most extensively studied among digeneans, there are still gaps in our knowledge regarding the distribution patterns of some neuroactive substances, most notably neuropeptides. The present study addresses these gaps by studying pre-infective metacercariae of D. pseudospathaceum using immunochemical staining and confocal microscopy to characterize the distribution patterns of serotonin (5-HT) and two major groups of flatworm neuropeptides, FMRFamide-related (FaRPs) and substance P-related (SP) peptides. The general morphology of the nervous system was examined with antibodies to alpha-tubulin. The nervous system of the metacercariae was shown to conform to the most common morphology of the nervous system in the hermaphroditic generation, with three pairs of posterior nerve cords and four pairs of anterior nerves. The patterns of FaRP- and 5-HT immunoreactivity (IR) were similar to those revealed in earlier studies by cholinesterase activity, which is in accordance with the known role of these neurotransmitters in controlling muscle activity in flatworms. The SP-IR nervous system was significantly different and consisted of mostly bipolar cells presumably acting as mechanoreceptors. The architecture of the nervous system in D. pseudospathaceum metacercariae is discussed in comparison to that in cercariae of D. pseudospathaceum and metacercariae of related digenean species.

Integrative taxonomy uses several sources of information to establish more robust species delimitation criteria. In this study, we followed that approach to describe two new species of allocreadiid trematodes from freshwater fish distributed in locations across Middle America. The new species were first recognized by using sequences of the domains D1-D3 of the ribosomal 28S rRNA gene and then, morphological data (light and scanning electron microscopy (SEM)), host association, and geographical distribution were considered as additional sources of information to complement the species delimitation and description. Auriculostoma tica n. sp. was found in the intestine of Gymnotus maculosus Albert and Miller in Costa Rica, while Wallinia anindoi n. sp. was found in the intestine of Astyanax aeneus (Günther) in Oaxaca and Chiapas, Mexico, as well as in a location of Guatemala. A phylogenetic analysis combining newly generated sequences of the two new species along with those available for other allocreadiids in GenBank, revealed that isolates of each species are reciprocally monophyletic, and also their interrelationships: Au. tica n. sp. is a sister taxon of Auriculostoma totonacapanensis Razo-Mendivil et al., 2014, and W. anindoi n. sp. is a sister taxon of Wallinia brasiliensis Dias, et al., 2018. Genetic distances for the 28S rRNA gene were estimated among the American species of allocreadiids and further supported the validity of the new species.

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

This investigation of Calicotyle affinis is the first ultrastructural description of the male reproductive system of a monocotylid monogenean. It has revealed numerous characteristics which are either new or clarify those determined from previous light microscopical observations on the morphology of Calicotyle spp. These include numerous individual testes, each surrounded by its own basal lamina; an ejaculatory bulb delimited by a basal lamina surrounded by two independent internal and external bands of muscles; a bipartite, but not fully divided, muscular chamber (an internal seminal vesicle) in the proximal region of the ejaculatory bulb; well-developed unicellular prostatic glands localised outside the ejaculatory bulb, the cytoplasmic extensions of which pass into the ejaculatory bulb, to form the ducts which open into the lumen of ejaculatory duct; and a male copulatory organ in the form of a coiled penis tube containing throughout its lumen a long, hollow stylet. The penis tube appears to be a modified prolongation of the ejaculatory duct and is supported by a basal lamina and muscle layers. The stylet wall consists of a homogenous, dense material with a narrow, denser inner lining; it is funnel-shaped proximally but narrows imperceptibly towards the distal end of the penis tube, and appears to be a derivative of the basal laminae of the ejaculatory bulb and distal ejaculatory duct. A comparative analysis of the nature of the stylet in relation to those found in free-living platyhelminths forms part of a search for characters useful for understanding monocotylid origins and relationships.

A new digenean species, Microphallus ochotensis sp. nov., was described from the intestine of Pacific eiders (Somateria mollissima v-nigrum) from the north of the Sea of Okhotsk. It differs from other microphallids in the structure of the metraterm, which consists of two distinct parts: a sac with spicule-like structures and a short muscular duct opening into the genital atrium. Mi. ochotensis forms a monophyletic clade together with other congeneric species in phylograms derived from the 28S and ITS2 rRNA gene. Its dixenous life cycle was elucidated with the use of the same molecular markers. Encysted metacercariae infective for birds develop inside sporocysts in the first intermediate host, an intertidal mollusc Falsicingula kurilensis. The morphology of metacercariae and adults was described with an emphasis on the structure of terminal genitalia. Considering that Falsicingula occurs at the Pacific coast of North America and that the Pacific eider is capable of trans-continental flights, the distribution of Mi. ochotensis might span the Pacific coast of Alaska and Canada. The range of its final hosts may presumably include other benthos-feeding marine ducks as well as shorebirds. We suggest that a broad occurrence of two-host life cycles in microphallids is associated with parasitism in birds migrating along sea coasts. The chances that migrating birds would stop at a site where both first and second intermediate hosts occur are relatively low. The presence of a single molluscan host in the life cycle increases the probability of transmission.

Studying the Helminthological Collection of Museo de La Plata (MLP-He), several specimens of digeneans, recovered parasitizing a long-winged harrier, Circus buffoni (Accipitridae) from Buenos Aires Argentina, were analysed. The morphological and morphometric analysis of these specimens revealed the presence of two strigeid species, one of them new for science. Parastrigea buffoni n. sp. is characterised by a forebody differentiated in a retractile cephalic region with a large opening and a balloon-shaped collar region or collerette, suckers located in cephalic region, holdfast organ with well development dorsal and ventral lips that can emerge through opening, a claviform hindbody, a large copulatory bursa with muscular ring (Ringnapf) and a genital cone well delimited, crossed by a sinuous hermaphroditic duct with internal rugae. The euryxenous parasite, Strigea falconis brasiliana, is briefly described, parasitizing a new host. This is the first record of helminths parasitizing long-winged harrier.

Trematodes of the family Orientocreadiidae are mostly parasites of freshwater fishes. Here, the phylogenetic position of this family is inferred based on the partial 28S rDNA sequence from a representative of the genus Orientocreadium s. str.-О. pseudobagri Yamaguti, 1934. Sequences were analysed by maximum likelihood and Bayesian inference algorithms. Both approaches placed the Orientocreadiidae within a clade corresponding to the superfamily Plagiorchioidea and supported the family Leptophallidae as a sister taxon.

Neodiplostomum americanum Chandler and Rausch, 1947 has been reported from six species of owls in North America. At present, there are no molecular data for this species and gene sequence data from Neodiplostomum Railliet, 1919 are limited. A freshly deceased specimen of the Great Horned Owl Bubo virginianus Gmelin, 1788 and a freshly deceased specimen of the Eastern Screech Owl Megascops asio Linnaeus, 1758 were collected in Oktibbeha County, Mississippi in 2014 and 2016, respectively. Neodiplostomum americanum were recovered from both hosts. Herein, updated morphological descriptions are supplemented with gene sequence data from conserved (18S, ITS1-5.8S, ITS2, and 28S rRNA) and fast-evolving (cytochrome c oxidase subunit 1 mtDNA) regions. Preliminary phylogenetic analysis of the genus based on cytochrome c oxidase subunit 1 gene sequence data supports the placement of N. americanum within a discrete phylogroup of the family Diplostomidae. The life history of N. americanum is unknown and currently limited to the description of the adult stage in avian hosts. The molecular data generated in this study offer insight into the phylogenetic placement of N. americanum within the Diplostomatidae and will aid in identifying different life stages in putative intermediate hosts.

Based on Cichlidogyrus sp. (Monogenea, Ancyrocephalidae) specimens from Hemichromis sp. hosts, we tested the influence of different methods to fix/preserve samples/specimens [frozen material, alcohol or formalin preserved, museum process for fish preservation (fixed in formalin and preserved in alcohol)] and different media used to mount the slides [tap water, glycerin ammonium picrate (GAP), Hoyer's one (HM)] on the size/shape of sclerotized parts of monogenean specimens. The results show that the use of HM significantly increases the size of haptoral sclerites [marginal hooks I, II, IV, V, and VI; dorsal bar length, width, distance between auricles and auricle length, ventral bar length and width], and changes their shape [angle opening between shaft and guard (outer and inner roots) in both ventral and dorsal anchors, ventral bar much wider, dorsal one less curved]. This influence seems to be reduced when specimens/samples are fixed in formalin. The systematics of Monogenea being based on the size and shape of their sclerotized parts, to prevent misidentifications or description of invalid new species, we recommend the use of GAP as mounting medium; Hoyer's one should be restricted to monogenean specimens fixed for a long time which are more shrunken.

M esostephanus appendiculatus (Family: Cyathocotylidae) is one of the unique trematodes that complete their cycles in human and animal intestines in many countries of the world. The main source of its transmission is eating raw or undercooked infected fish muscle. Earliest analyses of genes to different parasites supported the analysis of helminthes either biological or morphological. This paper detected M. appendiculatus sequence with GenBank accession number gb (KY026782). Comparison of M. appendiculatus with other helminthes using BioEdit 7 and MEGA7 program shows some similarity in different points along its sequence. The phylogenetic analysis clarifies that it was closely related to both trematodes (Clinostomum complanatum and Echinochasmus japonicus) and some cestodes of fish origin such as Polyonchobothrium polypteri, Bothriocephalus sp., and Haplobothrium globuliforme. The obtained results provide a good source for genome analysis of M. appendiculatus in relation to other Platyhelminthes.

Seventy-five previously frozen Northern Lapwings, Vanellus vanellus (Linnaeus, 1758) were dissected and examined for trematodes. The available birds were euthanized after suffering severe injuries from a hail storm. Trematode specimens were found in the air sacs, body cavities and kidneys. They were cleared, stained in Alaun-Carmine and examined via light microscopy. Trematodes were assigned to two different families and three different species: Uvitellina vanelli and Selfcoelum sp. from the family Cyclocoelidae and Tanaisia valida of the family Eucotylidae. A prevalence of 12% (for both, Cyclocoelid and Eucotylid infections) was detected. While trematodes of the respiratory system have been discovered in V. vanellus before, the present study describes renal trematodiasis in this bird species for the first time. Furthermore, the first recovering of a trematode of the species Selfcoelum sp. in the Northern Lapwing is described. Full measurements and figures of trematodes are given. Criteria and critical points in specifying and recovering the parasites are discussed.

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

A new genus and species of monogenean belonging to the Gyrodactylidae, Citharodactylus gagei n. gen. et n. sp. (Plathyhelminthes, Monogenea), is described from the gills of the moon fish, Citharinus citharus (Geoffroy Saint-Hilaire), a characiform fish collected from Lake Turkana in northern Kenya. The new viviparous genus can be readily distinguished from the six other gyrodactylid genera recorded from Africa and from the other viviparous genera within the Gyrodactylidae based on the morphology of the male copulatory organ (MCO), which consists of a muscular ovate organ with an opening onto the tegument through which the narrow tapered end of a sclerotised curved cone-shaped structure protrudes. The tegumental opening of the MCO is surrounded by a collar of short spines. Sequencing of the nuclear ribosomal DNA internal transcribed spacers 1 and 2, the 5.8S and the 18S rDNA genes and a comparison with the gyrodactylid species listed in GenBank confirmed the specimens are unique and do not match with any existing entry. When phylogenies for each genomic region were conducted (i.e. 0.064 gamma-corrected pairwise genetic distance based on a alignment of 1750 bp of the 1857 bp long 18S rDNA gene), the most similar match was that of Afrogyrodactylus sp. [= A. girgifae (Folia Parasitol 61:529-536, 2014)] from Brycinus nurse (Rüppell). The proposed name of the new parasite is Citharodactylus n. gen. which represents the seventh gyrodactylid genus to be found in Africa and the 25th viviparous genus and the 32nd genus to be added to the Gyrodactylidae.

An important question in the study of phenotypic evolution is whether characters are independent of each other or behave and evolve as integrated modules. Morphological integration and modularity provide a powerful framework for the analysis of the evolution of morphological traits. We used geometric morphometrics and phylogenetically independent contrasts (PIC) to test four different modularity hypotheses in the haptoral anchors of 14 monogenean species of Ligophorus. Integration between the modular units identified was further evaluated with two-block partial least squares analysis. Roots and points represented two modules in the dorsal and ventral anchors, but modularity was not statistically supported when parasite phylogeny was accounted for, which may indicate convergent evolution related to host characteristics and gill morphology. In contrast, PIC revealed medial and lateral modules in ventral anchors only. Moreover, we found evidence for ventral and dorsal anchor pairs forming two modules, supporting the notion that they play different functional roles. Integration between all identified modules was strong. We conclude that there is modular structure in the anchors of Ligophorus spp., accounted by adaptive and phylogenetic factors acting at different levels, and ventral and dorsal anchors evolve as integrated modules with specific roles in attachment.

Adult Orthocoelium parvipapillatum are common parasites that reside in the rumen and reticulum of ruminants, i.e., cattle, sheep, goats, and buffaloes. The fluke is conical-shaped and slightly concave ventrally and convex dorsally, and measures bout 2.4-3.9 mm in length and 1.0-2.3 mm in width across the mid-section. The tegument of the adult worm is examined using light microscopy (LM) and scanning (SEM) and transmission electron microscopy (TEM). Under LM, the tegument appears as a thick homogeneous layer containing folds alternated with grooves without spines. SEM revealed that the tegumental surface is highly corrugated with ridges and furrows and appears spineless. Two types of sensory papillae are observed, i.e., type 1 is bulbous in shape with nipple-like tips and type 2 has a similar shape with short cilia. In TEM, the tegument has a typical syncytial organization and is divided into four layers. The first layer of the tegument contains ridges and furrows covered by a trilaminate membrane coated externally with the glycocalyx. The second layer is a strait area of cytoplasm that includes numerous ovoid electron-lucent (TG1) and disc-shaped electron-dense (TG2) tegumental granules and lysosomes. The third layer is the widest middle area which contains several evenly distributed mitochondria, TG1 and TG2. The fourth layer rests on a thick basal lamina and contains numerous infoldings of the basal plasma membrane with closely associated mitochondria. Both granules are produced and transported to the tegument by one type of tegumental cells lying in rows below the muscular layers.

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

Species of Apatemon Szidat, 1928 and Australapatemon Sudarikov, 1959 are reported from New Zealand for the first time, and their life cycles are resolved using molecular sequence data (28S and ITS rDNA regions and mitochondrial COI). The metacercaria of Apatemon sp. 'jamiesoni' ex Gobiomorphus cotidianus and its cercaria ex Potamopyrgus antipodarum are described in detail. Its adult, found in Anas platyrhynchos and Phalacrocorax punctatus, is identified by molecular sequence data. Apatemon sp. 'jamiesoni' uses a different species of snail host, exhibits consistent differences in the genetic markers examined and its single described adult differs from known species so as to be considered distinct, but its formal description awaits additional adult specimens. Australapatemon niewiadomski n. sp. is described from Anas platyrhynchos. It is distinguished morphologically by the absence of a ringnapf and its overall smaller size compared to most other Australapatemon spp. except Au. magnacetabulum and Au. minor, which are smaller in nearly all features than the new species. Au. niewiadomski n. sp. metacercaria and its intermediate host (Barbronia weberi) are identified via matching of molecular sequence data. The status of Apatemon and Australapatemon as distinct genera is confirmed based on their respective monophyly, and genetic divergence between them is comparable to other well-established genera in the Strigeidae. The diagnosis of Australapatemon is emended. Life history data, accurate patterns of host specialisation and distribution, alongside concurrent molecular and morphological evidence would be useful for an integrative taxonomical approach towards the elucidation of species diversity in this group.

Eight new species of Gyrodactylus are described from Poecilia mexicana, Poeciliopsis gracilis, Pseudoxiphophorus bimaculatus [syn. = Heterandria bimaculata], and Xiphophorus hellerii collected in the Nautla and La Antigua River Basins in Veracruz, and in the Tecolutla River Basin in Puebla, Mexico. Analyzing the morphology of the marginal hooks, Gyrodactylus pseudobullatarudis n. sp. and Gyrodactylus xtachuna n. sp. are both very similar to Gyrodactylus bullatarudis; Gyrodactylus takoke n. sp. resembles Gyrodactylus xalapensis; Gyrodactylus lhkahuili n. sp. is similar to Gyrodactylus jarocho; and both Gyrodactylus microdactylus n. sp. and Gyrodactylus actzu n. sp. are similar to Gyrodactylus poeciliae in that all three species possess extremely short shaft points. A hypothesis of the systematic relationships of the eight new Gyrodactylus species and some of the known gyrodactylids infecting poeciliids was constructed with sequences of the Internal Transcribed Spacers (ITS1 and ITS2) and the 5.8S ribosomal gene of the rRNA. Phylogenetic trees showed that the new and previously described species of Gyrodactylus infecting poeciliid fishes do not form a monophyletic assemblage. Trees also showed that the eight new species described morphologically correspond to well-supported monophyletic groups; and that morphologically similar species are also phylogenetically close. Additionally, we correct previous erroneous records of the presence of Gyrodactylus bullatarudis on wild Poecilia mexicana and Xiphophorus hellerii collected in Mexico, as re-examination of the original specimens indicated that these corresponded to Gyrodactylus pseudobullatarudis n. sp. (infecting Poecilia mexicana and Xiphophorus hellerii) and to Gyrodactylus xtachuna n. sp. (on Xiphophorus hellerii). Finally, given the widespread anthropogenic translocation of poeciliid fishes for the aquarium trade and mosquito control programs, as well as the existence of invasive, feral poeciliid populations worldwide, we discuss the possibility that gyrodactylid parasites could be introduced along with the fish hosts-this work provides taxonomic information to assess that possibility, as it describes parasites collected from poeciliid fishes within their native distribution range.

Goldfish, Carassius auratus, widely distributed across Eurasia, is one of the earliest fish domesticated for ornamental purposes. A series of diseases break out due to high-density culture of goldfish, causing significant economic losses. Here, we report for the first time an infection of Gyrodactylus kobayashii associated with the high mortality of goldfish from a fish farm in Anziying township of Henan province, China, following their transfer to several aquariums. In the first 2 weeks after goldfish (n = 4200, weight 10.24 ± 1.45 g) transfer to aquariums, a total of 3335 goldfish were lost, representing 79.4 % of the initial stocked biomass. The examination showed that no other pathogens were found in this batch of fishes, except for G. kobayashii. The high burdens of G. kobayashii/fish (264.7, range 100-450) were the primary reason for the high mortality, although this was not the sole cause. In addition, the isolate of G. kobayashii from goldfish (C. auratus) in Henan province of central China was described. The morphological characterization was performed using morphometric measurements and drawings of opisthaptoral hard parts of the parasites. The molecular description was performed based on phylogenetic analysis of a reference DNA sequence spanning 5.8S and ITS-2. Importantly, the present study provides for the first time a full 25 point-to-point morphometric measurements and high-resolution images of attachment organ of G. kobayashii.

Ribosomal DNA sequences of Rhipidocotyle sp. adults from Esox lucius were shown to be identical to sequences of larval Rhipidocotyle fennica, occurring in Anodonta anatina in Lake Vilkokšnis, Lithuania. Morphological features and host specificity of this adult worm correspond with that, determinate in the first description of R. fennica in Finland. These data give the first evidence that a viable population of R. fennica exists in east central Europe. Bucephalus polymorphus which was reported in unionids in all previous publications is probably R. fennica.

Two new species of Annulotrema Paperna & Thurston, 1969 were collected from the gills of the African tiger fish, Hydrocynus brevis, from the Gambia River basin in the Niokolo-Koba National Park, Senegal. Annulotrema besalis n. sp. is characterized by having a male copulatory organ (MCO) composed of an arcuate copulatory tube articulated to an eight-shaped accessory piece with terminal claw. The new species resembles Annulotrema pikei (Price, Peebles & Bamford, 1969) in having morphologically similar types of haptoral sclerites and MCO. As a result of the differential diagnosis made for A. besalis n. sp., new information on taxonomically important features of A. pikei is provided based on illustrations of the sclerotized parts of the holotype from Hydrocynus vittatus. The report of A. pikei on the gills of Hydrocynus forskahlii by Paperna in 1979 is shown to be erroneous. Annulotrema uncata n. sp. is similar to Annulotrema alestesimberi Paperna, 1973 in its possession of a coiled copulatory tube with about two and a half rings. Features distinguishing the new species include the sharply curved shaft of the ventral anchor, the base of the copulatory tube extending to a sock-like structure and a leech-shaped vagina. The necessity of emending the generic diagnosis of Annulotrema is briefly discussed.

Two new species of the microphallid genus Maritrema (Maritrema) Nicoll, 1907 are described from freshwaters in the South Island of New Zealand. Maritrema deblocki n. sp. occurs as an adult in the mallard Anas platyrhynchos (L.); Maritrema poulini n. sp. is found as sporocysts/cercariae in Potamopyrgus antipodarum (Gray) and as metacercariae in two species of amphipod and two species of isopod. We use morphological and molecular characterisation to distinguish between the two species, and compare them to their four morphologically closest congeners. M. deblocki n. sp. and M. poulini n. sp. are distinguished from each other by the relative sucker size, the positions of the genital pore and ovary, the convergence of the vitelline ribbons, and overall size. With the aid of molecular data, we matched life cycle stages of M. poulini n. sp. and assessed its use of multiple second intermediate hosts. Phylogenetic analyses included sequences for the two new species and the available microphallid sequences for the large ribosomal subunit and the internal transcribed spacer 1 of the ribosomal RNA gene. Closer to each other than to any other species, the sister species together with Maritrema novaezealandense Martorelli, Fredensborg, Mouritsen & Poulin, 2004, Maritrema heardi (Kinsella & Deblock, 1994), Maritrema eroliae Yamaguti, 1939 and Maritrema oocysta (Lebour, 1907) formed a well-supported clade. In addition, we clarify the taxonomic identity of several unidentified Microphallus spp. in the recent ecological literature from New Zealand and propose corrected spellings for a number of Maritrema species epithets.

The musculature of cercariae, pre-ovigerous, and ovigerous adults of Diplodiscus subclavatus was studied by means of TRITC-conjugated phalloidin staining of filamentous actin and confocal scanning laser microscopy. The body wall appears to include four muscle layers as follows: circular, outer longitudinal, diagonal, and inner longitudinal. Two layers of longitudinal muscle fibers are arranged in different modes due to the secondary transformed paramphistomid body construction. The organization of the acetabulum turned out to be more complex than ever described, with a radial layer, two layers of circular, two layers of meridional, an additional starry layer of muscle fibers, as well as a few separate muscle layers of the accessory sucker. Within the pharynx, I found a group of alar muscle fibers, never described before for any paramphistomids, and some morphological features which were not considered to be characteristic for D. subclavatus (namely--the middle semicircular layer and the transverse muscle fibers in the pre-sphincteric space). No significant reorganizations of the somatic musculature occur throughout the development from the cercaria to the ovigerous adult worm, so the metamorphosis goes in the manner of completion. The cercarial tail includes a layer of circular muscle fibers and a longitudinal muscle layer beneath. The latter consists of two medial longitudinal bundles of smooth muscle fibers and two lateral longitudinal bands of obliquely striated muscle fibers which are partially divided in halves.

While Gobioidei comprises showcases of (adaptive) radiation, the scientific interest they yielded did not ensure full understanding of goby biodiversity. Even in a well-studied region like Europe, wide knowledge gaps remain. Sand gobies represent one of the few clades whose monogenean parasites have been thoroughly studied. However, in the Balkans, part of the sand gobies' centre of endemism, these parasites were unstudied. We focus on Greek and Croatian freshwater gobies. From five sand goby species, the first parasites are reported, describing seven new Gyrodactylus species. Economidichthys pygmaeus harbours Gyrodactylus benedeni sp. n. and Gyrodactylus dorlodoti sp. n. Its congener E. trichonis hosts G. meelkopae sp. n. Knipowitschia milleri was found to host G. charon sp. n., K. thessala is infected by G. bios sp. n., and K. croatica by G. douglasadamsi sp. n. and G. hellemansi sp. n. Gyrodactylus bubyri was found on its type host K. caucasica. A diverse parasite fauna is expected for a region known for its biodiversity and endemism. The contribution of parasites to species richness in such hotspots is overlooked. The observed species richness per host is rather low compared to the better-studied eastern Atlantic sand gobies. Host vicariance is considered to mediate parasite specificity in this fauna. Some new flatworm species display unique morphological features, such as the remarkable size of the marginal hook sickle proper compared to its foot in the Economidichthys parasites, or a characteristically kinked marginal hook sickle in G. douglasadamsi sp. n. These features reflect their hosts' endemism in the Balkans.

The gills of three of five species of mullets (Teleostei: Mugiliformes: Mugilidae) collected from the brackish and fresh waters of southern Iraq were infected with species of Ligophorus (Monogenoidea: Dactylogyridae) as follows: greenback mullet Chelon subviridis (Valenciennes) infected with Ligophorus lebedevi Dmitrieva, Gerasev, Gibson, Pronkina and Galli, 2012, Ligophorus bantingensis Soo and Lim, 2012, Ligophorus sagmarius n. sp., and Ligophorus fluviatilis (Bychowsky, 1949) Dmitrieva, Gerasev, Gibson, Pronkina, and Galli, 2012; Klunzinger’s mullet Liza klunzingeri (Day) with L. bantingensis, L. fluviatilis, and an apparently undescribed species of Ligophorus; and abu mullet Liza abu (Heckel) with L. bantingensis and L. fluviatilis. The keeled mullet Liza carinata (Valenciennes) and Speigler’s mullet Valamugil speigleri (Bleeker) were uninfected. L. sagmarius n. sp. is described, and L. lebedevi and L. bantingensis are redescribed. Available specimens of L. fluviatilis and the undescribed species of Ligophorus from Klunzinger’s mullet were insufficient for description.

In the first study of the vaginal ultrastructure of any monogenean, the paired vaginae of Chimaericola leptogaster, a basal polyopisthocotylean from the gills of a holocephalan, are described. Each vagina opens laterally. A unique feature of this relict parasite is a short vagino-intestinal connecting duct, the lining of which is separated by septate junctions from the linings of the vagina and the intestine. After giving rise to this vagino-intestinal duct, each vagina travels in a posterior direction and opens into the vitelline collecting duct. The lining of each vagina close to the vaginal pore resembles the body tegument, the syncytial lining of which measures about 2.5 μm in thickness and has a dense surface layer 0.2 μm in thickness and different apical projections. Proximal to this and before the entrance to the vaginal-intestinal duct, the vaginal lining is characterised by: uniformly distributed electron-dense, lanceolate, spine-like surface structures of about 1.7 μm in length; three kinds of surrounding glands with three kinds of secretory granules (abundant oval or rounded electron-dense granules 0.7-2.5 μm in length, much less numerous spheroidal, vesicular granules 0.3-0.4 μm in diameter, and tightly packed, spheroidal granules 0.8 μm in diameter and containing fine particulate material of low density); and four kinds of sensory receptors (three uniciliate and one aciliate). These features are absent from the rest of the vagina. The likely roles of the vagino-intestinal connection, the different gland cells, sensory structures, and the armament of the distal vaginal regions are discussed. Considering the suggested polyopisthocotylean ancestor for the Neodermata, the relict parasite fauna of holocephalans and the unique vagino-intestinal connection in C. leptogaster, which is also known in turbellarians, an ancient origin for chimaericolids is supported.

Phyllodistomum inecoli n. sp. is described from the twospot livebearer, Heterandria bimaculata (Teleostei: Poeciliidae), collected in the Río La Antigua basin, Veracruz, Mexico. The new species is described and characterised by using a combination of morphology, scanning electron microscopy, and sequences of nuclear and mitochondrial genes. Diagnostic characters of the new species of Phyllodistomum include a genital pore opening at the level of the caecal bifurcation; oval vitellarium, situated just posterior to the ventral sucker and not extended laterally and anterior extracaecal uterine loops variable in extension (reaching the anterior, median or posterior margin of the ventral sucker). P. inecoli n. sp. most closely resembles P. brevicecum, a species described as a parasite of the central mudminnow, Umbra limi, in other parts of North America; however, the genital pore in P. brevicecum is situated between the caecal bifurcation and the ventral sucker, the ovary is larger, the vitellarium is lobed and extended laterally and the anterior portion of the uterus extends to the posterior margin of the ventral sucker. Comparison of about 1,500–2,200 nucleotides of cox1 and 28S rDNA and ITS1 strongly supports the status of P. inecoli as a new species. Bayesian inference analysis of combined datasets of 28S rDNA and cox1 sequences showed that P. inecoli n. sp. and the other species found in freshwater fishes of Mexico, including the species complex of P. lacustri, are not sister species. Phylogenetic analysis based on 28S rDNA sequences of several gorgoderid taxa revealed the close relationship of P. inecoli n. sp. with several species of Phyllodistomum, Gorgodera and Gorgoderina with cystocercous cercariae developing in sphaeriid bivalves. Dot-plot analysis of ITS1 sequences of P. inecoli n. sp. revealed the presence of eight repetitive elements with different length, which together represent almost half the length of ITS1.