Filling the gaps in the classification of the Digenea Carus, 1863: systematic position of the Proterodiplostomidae Dubois, 1936 within the superfamily Diplostomoidea Poirier, 1886, inferred from nuclear and mitochondrial DNA sequences

Characterization of new 'white grub' parasites (Posthodiplostomum spp.) (Trematoda: Diplostomidae) in Georgia, USA, with descriptions of two new species and remarks on P. nanum Dubois, 1937

Posthodiplostomum Dubois, 1936 is a diverse, widespread genus of diplostomoideans that parasitize as adults the intestines of piscivorous birds. Larvae of Posthodiplostomum spp. commonly cause the 'white grub' disease of fishes. During July 2024, we collected Posthodiplostomum spp. from green heron Butorides virescens and great egret Ardea alba in Georgia, USA, including two new species. We provide descriptions of both new species in the present study. Partial nuclear 28S rDNA and mitochondrial cox1 gene DNA sequences were generated for all collected species; newly obtained 28S sequences were used to study the phylogenetic interrelationships among Posthodiplostomum spp. The new species have a subspherical prosoma that is characteristic in only a few other species, notably Posthodiplostomum aztlanensis and Posthodiplostomum nanum which parasitize the same avian host species. Despite minimal morphological differences among Posthodiplostomum seminolense n. sp., Posthodiplostomum dawnsherryae n. sp., P. aztlanensis and P. nanum, these morphologically similar species differ by 0.5-5.9% in partial 28S sequences and 10.9-17.4% in partial cox1 sequences. The original description of P. nanum was based on immature specimens; we provide a new description of P. nanum based on previously sequenced specimens from a great egret in Mississippi, USA to allow better comparisons.

Life cycle of the seabird digenean Gymnophallus minor (Gymnophallidae) in the Arctic

Gymnophallidae is one of the digenean families featuring bivalves as first intermediate hosts. However, the exact bivalve host species remain unknown for most members of this family. Gymnophallids have been one of the targets in our continuous efforts to reveal the diversity of digeneans in the higher north. Here, we focus on Gymnophallus minor, which we found in eiders from various locations in the Arctic and sub-Arctic. Sexual adults (maritae) of G. minor can be easily identified because they have a distinctive character: the roughly equal size of the pharynx and the ventral sucker. We also matched them, using DNA markers, with the intramolluscan stages (sporocysts, cercariae, and metacercariae) from the bivalve Liocyma fluctuosa collected on Spitsbergen. Taken together, we compile the first data on the life cycle of G. minor and discuss them in the context of other gymnophallids.

Intestinal helminths of bats in the States of Nayarit and Veracruz, Mexico, with redescription of Bidigiticauda vivipara Chitwood

Although surveys on bat parasites in the Americas have been conducted, information on helminths remains limited. In Mexican states such as Nayarit and Veracruz only 1 and 8 helminth species have been reported in bats, respectively. In this study, we provide new helminthological records for bats using morphological techniques. Also, the 28S rRNA gene of specimens from several helminth taxa was successfully amplified and sequenced. To confirm the identification at the generic level, and in some cases at the specific level, and the genealogical relationships of the parasites, we performed the phylogenetic analyses using the new 28S rRNA sequences. From March to May 2022, 16 bats of 10 species are captured and examined for helminths. Three bat species of two families, two Vespertillionidae (Bauerus dubiaquercus and Rhogeessa parvula) and one Phyllostomidae (Glossophaga mutica), are parasitized by helminths. Seven helminth taxa are morphologically identified: the trematodes Urotrema scabridum and Anenterotrema cf. hastati, the cestodes Vampirolepis macroti, Vampirolepis sp. (1), and Vampirolepis sp. (2), and the nematodes Bidigiticauda vivipara and Capillariidae gen. sp. The first helminthological records for R. parvula and B. dubiaquercus and the 28S rRNA gene data of B. vivipara, V. macroti, and Vampirolepis spp. are provided. The findings of the present study increase the number of helminth taxa recorded in Mexican bats from 78 to 79, as well as the number of bat species with helminthological records from 35 to 37.

A new species of Heligmostrongylus Travassos 1917 (Nematoda: Heligmonellidae) in small rodents (Cricetidae and Heteromyidae) from Mexico

A new species of Heligmostrongylus (Nematoda: Heligmonellidae) is described from the small rodents Ototylomys phyllotis (Cricetidae: Tylomyinae) and Heteromys gaumeri (Heteromyidae: Heteromyinae) in the Yucatan Peninsula, Mexico, based on studies of light and scanning electron microscopy, and partial sequences of COI, ITS1 and 28S rRNA. Heligmostrongylus yucatanensis n. sp. is characterized by a synlophe of 13 interrupted ridges (except those forming careen) in both sexes at midbody; males with a ventral cuticle inflation at anterior region of copulatory bursa, rays 9 and 10 long, comparable in length, and rays 9 strongly curved laterally at a right angle crossing ventrally rays 8; and females with a torsion of 180° to left of the posterior extremity. These characteristics were shared with Heligmostrongylus nematodes reported previously from O. phyllotis and Peromyscus yucatanicus (Cricetidae: Neotominae) also in the Yucatan Peninsula. The absence of intraspecific sequence variations in COI, and the low variation in D2-D3 expansion segments of 28S rRNA and ITS1 among the specimens obtained from the different hosts provided strong support that the worms found in the three rodent species belong to the same new species. The nine previously known species of Heligmostrongylus have been reported from caviomorph rodents of the families Cuniculidae, Dasyproctidae, Echimyidae, and Erethizontidae from the Neotropics. The occurrence of H. yucatanensis in three phylogenetically distant rodent species suggests that this nematode species could have the ability to expand its host range by colonizing new hosts.

A New Species of Creptotrematina (Trematoda: Allocreadiidae) from the Red Minor Tetra, Hyphessobrycon eques (Steindachner, 1882) (Characidae) from Brazil, with Comments on the Genetic Divergence of C. Aguirrepequenoi Jiménez-Guzmán, 1973 across a Wide Geographical Range in Middle America

BACKGROUND

Allocreadiids are relatively small digeneans that appear to be restricted to freshwater systems distributed across the world. Allocreadiids are highly diverse in the Americas, particularly in the Neotropical biogeographical region. Their taxonomic history has been rather controversial, with several taxonomic reassessments and the description of new genera and species.

METHODS

We sampled Creptotrematina specimens from a characid collected in the Pardo River, Paranapanema River basin in Brazil, and specimens of C. aguirrepequenoi, from Astyanax spp. in several localities between northern Mexico and Costa Rica. The specimens were studied through integrative approaches using morphological and molecular analyses of the 28S rDNA gene and two different regions of the COI mtDNA gene.

RESULTS

We describe a new species of Creptotrematina which is differentiated from other congeners by the overall body size, but in particular by the size and position of the cirrus-sac, distribution of the vitelline follicles, and extension of uterine loops in the posterior end of body. Phylogenetic analyses of the 28S rDNA and COI mtDNA genes placed the new species in a monophyletic clade together with all other sequenced species of Creptotrematina, and as a sister species of C. batalhensis. Genetic divergences between the new species and other Creptotrematina spp. varied from 1.1 to 1.2% for the 28S rDNA and 12.4-14.3% for the COI mtDNA. Phylogenetic analysis based on COI mtDNA showed the isolates of C. aguirrepequenoi grouped in four monophyletic clades representing populations geographically separated along a wide geographical range spanning between northern Mexico and Costa Rica, with an estimated genetic divergence between 3.9% and 8.9%.

CONCLUSIONS

Our findings based on integrative analyses recognize Creptotrematina saltograndensis n. sp. from a characid collected in the Pardo River, Paranapanema River basin in Brazil and provide validation of the wide geographical distribution of C. aguirrepequenoi across Middle-America parasitizing Astyanax spp.; the genetic divergence of the species through the analysis of two regions of COI mtDNA points towards considering it represent a species complex, although we refrain at the moment on describing a new species, awaiting for further verification using other molecular markers, and obtaining fresh material for a more detailed taxonomic analyses. This study increases the known diversity of allocreadiids and contributes to the understanding of evolutionary relationships, host-parasite relationships, and biogeographic history of the group.

PHYLOGENY AND SYSTEMATICS OF CYATHOCOTYLID DIGENEANS (DIGENEA: DIPLOSTOMOIDEA) PARASITIZING SNAKES WITH DESCRIPTION OF THREE NEW SPECIES OF GOGATEA FROM AUSTRALIA AND VIETNAM

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

A new species of Creptotrema (Allocreadiidae) in Cambeva davisi (Siluriformes) from river streams in fragments of the Atlantic Rainforest, southern Brazil

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

Prevalence and identification of cyathocotylid trematodes infecting African catfish in Egypt

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.

Proterodiplostomid no longer: Molecular phylogeny reveals the true position of Proalarioides (Digenea: Diplostomoidea)

Proalarioides Yamaguti, 1933 (Digenea Carus, 1863: Diplostomoidea Poirier, 1886) is a small genus of proterodiplostomids parasitic in the intestines of snakes in Asia. Only two species are considered valid: Proalarioides serpentis Yamaguti, 1933 and Proalarioides tropidonotis Vidyarthi, 1937. Unlike other proterodiplostomids, Proalarioides spp. possess pseudosuckers and lack the paraprostate, otherwise extremely characteristic of the Proterodiplostomidae Dubois, 1936. In the present study, we describe the morphology of progenetic metacercariae of a Proalarioides sp. from bicolored frog, Clinotarsus curtipes (Jerdon), collected in India and provide the first DNA sequences from any member of the genus. These specimens differ from previously described metacercariae and adults of P. serpentis and P. tropidonotis in several ways, including body and organ sizes, sucker ratios, and distribution of vitellarium. The newly generated partial large ribosomal subunit (28S) rRNA gene sequence was used to test the phylogenetic position of the genus among other major lineages of diplostomoideans. Our 28S phylogeny clearly demonstrated Proalarioides sp. to be well-separated from other members of the Proterodiplostomidae. Based on morphological and molecular evidence, we transfer Proalarioides out of the Proterodiplostomidae into the Diplostomidae Poirier, 1886.

Unravelling the diversity of Posthodiplostomum Dubois, 1936 (Trematoda: Diplostomidae) in fish-eating birds from the Neotropical region of Mexico, with the description of a new species

Adults of the genus Posthodiplostomum, Dubois, 1936 are parasites of fish-eating birds, mainly of the family Ardeidae, and are globally distributed. The genus currently comprises 35 species, although recent molecular evidence has shown that the diversity of the genus is underestimated since several candidate species have been recognized. In the Neotropical region of Mexico, at least 6 Posthodiplostomum lineages have been detected with metacercaria stages recovered from unrelated fish hosts. Here, we obtained adult specimens of Posthodiplostomum from 6 fish-eating birds representing 2 families (Butorides virescens, Ardea herodias, Nycticorax nycticorax, Tigrisoma mexicanum – Ardeidae, and Rynchops niger and Leucophaeus atricilla – Lariidae) from 4 localities in southern Mexico. Specimens were sequenced for 2 nuclear (28S and ITS1–5.8S–ITS2) and 1 mitochondrial (cox1) molecular marker. Phylogenetic analyses allowed us to link metacercariae and adult specimens and recognized a lineage, which was described morphologically. The new species can be distinguished from its congeners by its prosoma morphology and body size; this is the first described species in the Neotropical region of Mexico. Additionally, new host and locality records for P. macrocotyle and P. pricei are presented, expanding their geographical distribution range in the Americas.

Morphological and molecular data on helminths of Didelphis virginiana and Philander vossi (Mammalia: Didelphidae) from the Yucatán Peninsula, southeast Mexico

In the present study, helminths from six Didelphis virginiana and one Philander vossi are reported using morphological techniques (clearing, staining, and scanning electron microscopy). Additionally, the 28S rRNA sequences of individuals from nine helminth taxa are provided. Phylogenetic analyses were performed with the new 28S rRNA sequences to confirm the identification and the genealogical relationships of the parasites. Thirteen helminth taxa were identified, comprising the trematodes Brachylaima sp. and Platynosomum illiciens, the cestode Mathevotaenia sp., the nematodes Cruzia americana, Cruzia tentaculata, Viannaia arriaguensis, Viannaia sp., Travassostrongylus sp., Strongyloides sp., Turgida turgida, Trichuris minuta, and Trichuris sp., and the acanthocephalan Oligacanthorhynchus microcephalus. All opossums were infected with at least four helminth taxa. In total, 17 new 28S rRNA sequences from nine helminth taxa were provided. These data, combined with previous records in Mexico, increase the number of helminth taxa parasitizing D. virginiana and P. vossi to 41 and 29, respectively. However, these reports are incompletes and concentered in localities of some states. It is possible that new surveys in the Nearctic and even Neotropical regions will reveal a higher helminth diversity in these mammals in the country.

Uncovering further diversity of Ochoterenatrema Caballero, 1943 (Digenea: Lecithodendriidae) in South American bats

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

NEW RECORDS OF HELMINTHS OF THE JAGUAR IN MEXICO, WITH AN UPDATED LIST OF SPECIES IN THE AMERICAS

An inventory of parasites infecting the jaguar (Panthera onca) across its distribution range is relevant for the conservation of this threatened big cat. In this study, we report the occurrence of helminths in a jaguar from Mexico using morphological techniques (cleared and stained mounts and scanning electron microscopy) and partial sequences of the 28S ribosomal RNA (28S rRNA) gene and the cytochrome c oxidase 1 mitochondrial (COI) gene. We also provide an updated list of helminth species reported in jaguars in the Americas. Three helminth taxa are identified in the jaguar examined from Mexico: Toxocara cati, Physaloptera sp., and Taenia sp. The new 28S rRNA sequences of To. cati, Physaloptera sp., and Taenia sp. and the COI sequence of Taenia sp. corroborate the identity of the helminths isolated from this host. One hundred and twenty-nine records of helminths parasitizing jaguars from 49 studies up to May 2023 were identified in the Americas. In most of these studies (73.6%), helminths were identified using coproparasitological techniques. Sixteen helminths (7 nematodes, 5 cestodes, 3 acanthocephalans, and 1 trematode) were identified at the species level in free-ranging and captive jaguars. The study demonstrates the value of an integrative taxonomy approach to increase the accuracy of parasite identification in wildlife, especially when helminth specimens are scarce or poorly fixed.

First species record of Strigea falconis Szidat, 1928 (Trematoda, Strigeidae) from gyrfalcon Falco rusticolus in Iceland-pros and cons of a complex life cycle

Strigea falconis is a common parasite of birds of prey and owls widely distributed in the Holarctic. We aimed to characterise S. falconis from Iceland via integrative taxonomic approach and to contribute to the understanding of its circulation in the Holarctic. We recovered adult S. falconis from two gyrfalcons (Falco rusticolus) collected in 2011 and 2012 in Iceland (Reykjanes Peninsula, Westfjords) and characterised them by morphological and molecular genetic (D2 of rDNA, cox1, ND1 of the mDNA) methods. We provide the first species record of S. falconis in Iceland which to the best of our knowledge is its northernmost distributional range. The presence of S. falconis in Iceland is surprising, as there are no suitable intermediate hosts allowing completion of its life cycle. Gyrfalcons are fully sedentary in Iceland; thus, the only plausible explanation is that they acquired their infection by preying upon migratory birds arriving from Europe. Our data indicate that the most likely candidates are Anseriformes and Charadriiformes. Also, we corroborate the wide geographical distribution of S. falconis, as we found a high degree of similarity between our haplotypes and sequences of mesocercariae from frogs in France and of a metacercaria from Turdus naumanni in Japan, and adults from Buteo buteo and Circus aeruginosus from the Czech Republic. The case of Strigea falconis shows the advantages of a complex life cycle and also depicts its pitfalls when a parasite is introduced to a new area with no suitable intermediate hosts. In Iceland, gyrfalcons are apparently dead-end hosts for S. falconis.

Phylogenetic relationship of Prohemistomum vivax to other trematodes based on the internal transcribed spacer region and mitochondrial genes

Prohemistomum vivax is a zoonotic small cyathocotylid trematode that inhabits the intestines of fish-eating birds and mammals. Here, we amplified the internal transcribed spacer (ITS) sequence and six mitochondrial protein-coding genes (PCGs) from P. vivax. The ITS region was 1389 base pairs long and had a partial 18S ribosomal RNA gene, a full ITS1, 5.8S rRNA, and ITS2 sequence, and a partial 28S rRNA gene. The ITS region of P. vivax showed a minimum pairwise distance (0.3-0.6%) from the ITS sequences of Cyathocotylidae sp. 1 and 2 metacercariae from Clarias gariepinus. This result suggests that these metacercariae belong to P. vivax metacercariae. We first amplified mitochondrial genes from P. vivax, including cytochrome c oxidase subunit III (cox3) partial sequence; tRNA-His, cytochrome b (cytb), and NADH dehydrogenase subunit 4L (nad4L) complete sequences; and NADH dehydrogenase subunit 4 (nad4), cytochrome c oxidase I (cox1), and NADH dehydrogenase subunit 5 (nad5) partial sequences. P. vivax was most closely related to Cyathocotyle prussica (NC_039780) and Holostephanus sp. (OP082179), with cox1, cox3, and cytb genes conserved among the three trematodes. The ML phylogenetic tree of ITS sequences supports the order Diplostomida, divided into two main clades (the superfamily Diplostomoidea and Schistosomatoidea). The phylogeny of concatenated amino acid sequences of P. vivax six PCGs revealed that diplostomoids and Clinostomum sp. evolved in a clade with Plagiorchiida members, away from Schistosoma species. These results may yield ribosomal and mitochondrial genetic markers for molecular epidemiological investigations of cyathocotylid intestinal flukes.

The Systematics of the Trematoda

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

Other Schistosomatoidea and Diplostomoidea

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis (schistosomiasis) affecting more than 200 million people in tropical and subtropical countries, and infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The "Aporocotylidae" sensu lato are pathogenic in fish, "Spirorchiidae" sensu lato in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in mollusks and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

Helminths of small rodents (Heteromyidae and Cricetidae) in the Yucatan Peninsula, Mexico: an integrative taxonomic approach to their inventory

In this survey, we inventoried the helminths of heteromyid and cricetid rodents captured in the Yucatan Peninsula from 2017 to 2019. Helminths were identified using morphological techniques (clearing, staining, and scanning electron microscopy). Also, the 28S rRNA gene of individuals from several helminth taxa was successfully amplified and sequenced. To confirm the identification at the generic level, and in some cases at the specific level, and the genealogical relationships of the parasites, phylogenetic analyses were performed with the new 28S sequences. We identified 22 species of helminths including three trematodes (Brachylaimidae, Dicrocoeliidae, and Microphallidae), five cestodes (Davaineidae, Hymenolepididae, and Taeniidae), and 14 nematodes (Trichuridae, Ancylostomatidae, Ornithostrongylidae, Heligmonellidae, and Oxyuridae) from Heteromys gaumeri (Heteromyidae), Ototylomys phyllotis, Oligoryzomys fulvescens, Peromyscus yucatanicus, Sigmodon toltecus, and Reithrodontomys gracilis (Cricetidae). The overall frequency of infection in small rodents was 84.1% (143/170); all specimens of H. gaumeri, S. toltecus and Ol. fulvescens were infected with helminths. In total, we provided 46 new sequences of the 28S gene from 17 species of helminths. Seven species are likely undescribed species, six are reported for the first time in rodents from Mexico, and 12 are new host records in the Americas. Before this study, 87 taxa of helminths had been reported from 35 cricetid and 12 heteromyid species in 21 Mexican states. Our findings increase to 93 the helminth taxa in these rodents, and to 36 the cricetid species parasitized by helminths. This large scale-survey is the first to use an integrative approach to inventory the helminths of wild small rodents in Mexico.

Description and Phylogenetic Relationships of Anhingatrema n. gen. (Digenea: Diplostomidae) with Two New Species from New World Anhingas (Aves: Anhingidae)

PURPOSE

The Diplostomidae is a globally distributed family of digeneans that parasitize a wide variety of tetrapod definitive hosts. Recent molecular phylogenetic studies have revealed unknown diplostomid diversity in avian hosts throughout the New World. Herein, we provide descriptions of a novel genus of diplostomids with two new species.

METHODS

Two species of diplostomids belonging to the new genus were collected from anhinga birds in Mississippi (USA) and Brazil. Partial nuclear 28S ribosomal and mitochondrial cox1 genes were sequenced. Ribosomal data were used for phylogenetic inference.

RESULTS

Both species of Anhingatrema n. gen. were positioned in a 100% supported, monophyletic clade in the phylogenetic tree. The molecular phylogenetic position and a combination of morphological features (e.g., presence of pseudosuckers, testes shape and orientation) supported erection of the new genus. Anhingatrema overstreeti n. sp. and Anhingatrema cararai n. sp. are morphologically similar, but differ in size of and ratios associated with pseudosuckers. The two species differ by 2% of 28S sequences and 13.8% of cox1 sequences. Comparison of DNA sequences revealed that Diplostomidae gen. sp. in GenBank (MZ314151) is conspecific with An. overstreeti n. sp.

CONCLUSION

Anhingatrema n. gen. is the sixth genus of diplostomids known from anhingas worldwide. Anhingatrema cararai n. sp. is the first diplostomid to be reported from anhingas in South America. Combined with previous studies, the molecular phylogenies revealed at least two host switches to anhingas from other birds during the evolutionary history of the Diplostomidae.

Survey on helminths of bats in the Yucatan Peninsula: infection levels, molecular information and host-parasite networks

Helminth species of Neotropical bats are poorly known. In Mexico, few studies have been conducted on helminths of bats, especially in regions such as the Yucatan Peninsula where Chiroptera is the mammalian order with the greatest number of species. In this study, we characterized morphologically and molecularly the helminth species of bats and explored their infection levels and parasite–host interactions in the Yucatan Peninsula, Mexico. One hundred and sixty-three bats (representing 21 species) were captured between 2017 and 2022 in 15 sites throughout the Yucatan Peninsula. Conventional morphological techniques and molecular tools were used with the 28S gene to identify the collected helminths. Host–parasite network analyses were carried out to explore interactions by focusing on the level of host species. Helminths were found in 44 (26.9%) bats of 12 species. Twenty helminth taxa were recorded (7 trematodes, 3 cestodes and 10 nematodes), including 4 new host records for the Americas. Prevalence and mean intensity of infection values ranged from 7.1 to 100% and from 1 to 56, respectively. Molecular analyses confirmed the identity of some helminths at species and genus levels; however, some sequences did not correspond to any of the species available on GenBank. The parasite–host network suggests that most of the helminths recorded in bats were host-specific. The highest helminth richness was found in insectivorous bats. This study increases our knowledge of helminths parasitizing Neotropical bats, adding new records and nucleotide sequences.

No Tail No Fail: Life Cycles of the Zoogonidae (Digenea)

The Zoogonidae is the only digenean family where known cercariae lack the tail but actively search for the second intermediate host. However, the data on the zoogonid life cycles are scarce. In the present study, we elucidated and verified life cycles of the Zoogonidae from the White Sea. Using rDNA data, we showed that Pseudozoogonoides subaequiporus utilizes gastropods from the family Buccinidae as the first intermediate host and protobranch bivalves as the second one. This life cycle can be facultatively truncated: some cercariae of P. subaequiporus encyst within the daughter sporocysts. Molecular data also confirmed previous hypotheses on Zoogonoides viviapus life cycle with buccinid gastropods acting as the first intermediate hosts, and annelids and bivalves as the second intermediate hosts. We demonstrated the presence of short tail primordium in the developing cercariae of both species. Based on the reviewed and our own data, we hypothesize that the emergence of tailless cercariae in the evolution of the Zoogonidae is linked to the switch to non-arthropod second intermediate hosts, and that it possibly happened only in the subfamily Zoogoninae. Basally branching zoogonids have retained the ancestral second intermediate host and might have also retained the tail.

Phylogenetic relationships and further unknown diversity of diplostomids (Diplostomida: Diplostomidae) parasitic in kingfishers

Kingfishers (Alcedinidae Rafinesque) are common inhabitants of wetlands and are known to be definitive hosts to a wide range of digeneans that parasitize fish as second intermediate hosts. Among these digeneans, members of the Diplostomidae Poirier, 1886 (diplostomids) are particularly common. Recent studies of diplostomids collected from kingfishers have revealed that they are probably more diverse than currently known. This particularly concerns the genera Crassiphiala Van Haitsma, 1925 and Uvulifer Yamaguti, 1934. In the present work, we studied seven diplostomid taxa from kingfishers in Brazil, the USA and the Philippines. Partial DNA sequences of the nuclear large ribosomal subunit (28S) and mitochondrial cytochrome c oxidase I (cox1) genes were obtained, and 28S sequences were used to study the phylogenetic interrelationships of these diplostomids. We provide the first DNA sequences from Uvulifer semicircumcisus Dubois et Rausch, 1950 and a member of Subuvulifer Dubois, 1952. Pseudocrassiphiala n. gen. is erected for a previously recognized species-level lineage of Crassiphiala and a new generic diagnosis of Crassiphiala is provided. Crassiphiala jeffreybelli n. sp., Crassiphiala wecksteini n. sp. and Pseudocrassiphiala tulipifera n. sp. are described, and a description of newly collected, high-quality specimens of Crassiphiala bulboglossa Van Haitsma, 1925 (the type-species of the genus) is provided.

Species complexes and life cycles of digenetic trematodes from the family Derogenidae

The best way to study digenean diversity combines molecular genetic methods, life-cycle studies and elaborate morphological descriptions. This approach has been barely used for one of the most widespread digenean taxa parasitizing fish – the superfamily Hemiuroidea. Here, we applied the integrative approach to the hemiuroideans from the family Derogenidae parasitizing fish at the White and Barents Seas. Analysis of 28S, 18S, 5.8S rDNA, ITS2 and cox1 gene sequences from sexually adult worms (maritae) showed genetic heterogeneity for 2 derogenid species known from this area: Derogenes varicus and Progonus muelleri. Thus, 2 pairs of genetic lineages were found: DV1 and DV2, PM1 and PM2, respectively. Data from other regions indicate that 2 more lineages of D. varicus probably exist. Based on previous records from the White and Barents Seas, we hypothesized that the cercariae found in the moonsnails (family Naticidae) belong to the Derogenidae and may help to differentiate these lineages as species. According to our results, Cercaria appendiculata from Cryptonatica affinis matched DV1, similar nameless cercariae from Euspira pallida and Amauropsis islandica matched DV2, and Cercaria octocauda from C. affinis matched PM1. We provide new data on the structure of these cercariae and discuss the life-cycle pattern of the studied digeneans.

Immune pathogenesis in pigeons during experimental Prohemistomum vivax infection

Prohemistomum vivax is a small trematode belonging to the family Cyathocotylidae, infecting fish-eating birds and mammals, including humans. However, no data on molecular identification and immune pathogenesis are available, challenging effective diagnostic and therapeutic interventions. Here, we identified P. vivax based on combined morphological and molecular data and examined histopathological lesions and the differential cytokines expression in experimentally infected pigeons. Pigeons were orally infected with 500 prohemistomid metacercariae. Intestinal and spleen tissues were harvested 2, 4, 7, 14, 21, and 28 days post-infection (dpi). Gene expression levels of eleven cytokines (IL-1, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, IL-15, IL-18, IFN-γ, and TGF-β3) were assessed using quantitative reverse-transcription PCR (RT-qPCR). We identified the recovered flukes as Prohemistomum vivax based on morphological features and the sequence and phylogenetic analysis of the internal transcribed spacer 1 (ITS1), 5.8 ribosomal RNA, and ITS2 region. Histopathological lesions were induced as early as 2 dpi, with the intensity of villi atrophy and inflammatory cell infiltration increasing as the infection progressed. An early immunosuppressive state (2 and 4 dpi), with TGF-β3 overexpression, developed to allow parasite colonization. A mixed Th1/Th2 immune response (overexpressed IFN-γ, IL-12, IL-2, IL-4, and IL-5) was activated as the infection progressed from 7 to 28 dpi. Inflammatory cytokines (IL-1, IL-6, IL-18, and IL-15) were generally overexpressed at 7–28 dpi, peaking at 7 or 14 dpi. The upregulated Treg IL-10 expression peaking between 21 and 28 dpi might promote the Th1/Th2 balance and immune homeostasis to protect the host from excessive tissue pathology and inflammation. The intestine and spleen expressed a significantly different relative quantity of cytokines throughout the infection. To conclude, our results presented distinct cytokine alteration throughout P. vivax infection in pigeons, which may aid in understanding the immune pathogenesis and host defense mechanism against this infection.

Metacercariae in the brain of Erythrinus cf. erythrinus (Characiformes: Erythrinidae) from Iguazú National Park (Argentina): do they belong to Dolichorchis lacombeensis (Digenea, Diplostomidae)?

In Argentina, the family Diplostomidae is composed of eight genera: Austrodiplostomum Szidat & Nani; Diplostomum von Nordmann; Dolichorchis Dubois; Hysteromorpha Lutz; Neodiplostomum Railliet; Posthodiplostomum Dubois; Sphincterodiplostomum Dubois; and Tylodelphys Diesing. During a parasitological survey of fishes from the Iguazú National Park we detected diplostomid metacercariae in the brain of Erythrinus cf. erythrinus. Fish were caught using crab traps, transported alive to the field laboratory, cold-anaesthetized and euthanized by cervical dissection. Some metacercariae were heat-killed in water and fixed in 10% formalin and others were preserved in alcohol 96% for DNA extraction. They were sequenced for the partial segment of the 28S rDNA, internal transcribed spacer (ITS) rDNA and cytochrome c oxidase subunit I (COI) mtDNA genes. Phylogenetic reconstruction was carried out using Bayesian inference and the proportion (p) of absolute nucleotide sites (p-distance) was obtained. In the 28S rDNA tree, the metacercaria sequenced grouped as Dolichorchis sp. The COI mtDNA p-distance between the metacercariae with Dolichorchis lacombeensis was 0.01. There is a small number of ITS sequences for the Diplostomidae family deposited in the GenBank. The oral sucker, ventral sucker, holdfast organ and the distance between oral and ventral suckers are larger in the adult compared with the metacercariae. Additionally, hind-body length and width are larger in the adult due to the development of the genital complex. Further studies using an integrative approach will help confirm the affiliation of other species to the genus Dolichorchis.

Occurrence of Ancylostoma Caninum from a Gray Fox Urocyon Cinereoargenteus in Southeastern Mexico

The hookworm Ancylostoma caninum is a common nematode of wild and domestic canids worldwide. In Mexico, there are few records of helminths in wild canids, especially in the southeastern region. The aim of the present study was to examine the helminths from a gray fox Urocyon cinereoargenteus in southeastern Mexico. A road-killed female gray fox found in Merida, Yucatan, Mexico, was examined for helminths. Only nematodes were found in the intestine of the gray fox and identified using morphological studies and molecular analysis of 28S rRNA gene fragments. The characteristics exhibited by the nematode specimens were in accordance with descriptions of A. caninum: e. g. oral opening with a pair of prominent chitinous plates bearing three pairs of ventral teeth, lateral rays with a common trunk, dorsal ray divided into two branches with each branch terminating in three digitations. BLAST analysis of the 28S sequence showed similarity and coverage values of 99.8 % and 100 %, respectively, with a sequence of A. caninum from the domestic dog Canis familiaris in Australia. The genetic distance between the Australian specimen and the Yucatan specimen of A. caninum was 0.1 %, that is, they were only different in a single nucleotide. The gray fox examined in this study was found close to a rural community where A. caninum has been recorded from domestic dogs, which could be the source of infection. Our study increases the distribution of this nematode parasitizing the gray fox in Mexico and provides the first nucleotide sequence of A. caninum from the gray fox.

Integration of morphological and molecular data reveals further unknown diversity of the Proterodiplostomidae in crocodilians

The Proterodiplostomidae Dubois, 1936 is a family of digeneans within the superfamily Diplostomoidea Poirier, 1886. Members of the family are distributed mostly in the tropics and subtropics, primarily in crocodilians, although some species are known from other reptiles. Despite their broad geographical distribution, the knowledge of proterodiplostomid diversity remains limited, mostly because a number of potential host species and regions of the world have not been sufficiently explored for these parasites. In this study, we use morphological and molecular data to describe four new genera (Afroproterodiplostomum gen. nov., Dungalabatrema gen. nov., Australiadiplostomum gen. nov. and Nattererodiplostomum gen. nov.) and five new species (Afroproterodiplostomum ingwenyae sp. nov., Australiadiplostomum blairi sp. nov., Dungalabatrema kostadinovae sp. nov., Dungalabatrema snyderi sp. nov. and Pseudoneodiplostomum angustus sp. nov.) of proterodiplostomids from crocodilians in Australia, South Africa and South America. Nattererodiplostomum gen. nov. has been established upon re-evaluation of the status of Proterodiplostomum medusae (Dubois, 1936) from caimans in Brazil using combined morphological and molecular evidence. Only a few previous studies provided DNA sequence data of proterodiplostomids. We generated partial 28S rDNA and cytochrome c subunit (cox1) mtDNA for three previously undescribed proterodiplostomids collected from Crocodylus spp. in Australia and South Africa. The newly generated 28S sequences were used to examine phylogenetic affinities of these taxa. All three newly sequenced proterodiplostomid species appeared in the phylogenetic tree in a strongly supported monophyletic clade comprising exclusively parasites of Crocodylus.

Paraharmotrema karinganiense n. gen., n. sp. (Digenea: Liolopidae) infecting the intestine of serrated hinged terrapin (Pelusios sinuatus), east African black mud turtle (Pelusios subniger), and South African helmeted turtle (Pelomedusa galeata) and a phylogenetic hypothesis for liolopid genera

We herein describe Paraharmotrema karinganiense n. gen., n. sp. Dutton & Bullard (Liolopidae Dollfus, 1934) from specimens infecting the intestine of the serrated hinged terrapin (Pelusios sinuatus), east African black mud turtle (Pelusios subniger) (both Nwanedzi River, Mozambique), and South African helmeted terrapin (Pelomedusa galeata) (North-western Zululand, KwaZulu-Natal Province, South Africa). The new genus can be easily differentiated from the other accepted liolopid genera (Liolope Cohn, 1902; Helicotrema Odhner, 1912; Harmotrema Nicoll, 1914; Dracovermis Brooks & Overstreet, 1978) by the combination of having a linguliform body approximately 6-9 × longer than wide, tegumental spines/scales, a minute ventral sucker located in the anterior 1/7-1/8 of the body, deeply lobed testes that are transverse and abut the caeca (spanning the intercaecal space), a uterus that is lateral to the anterior testis (not ventral to the anterior testis), a lobed ovary that is dextral and nearest the posterior testis, and a vitellarium that does not extend anteriad to the level of the ventral sucker and that does not fill the intercaecal space. Nucleotide sequences of large subunit ribosomal DNA (28S) and internal transcribed space region (ITS2) from all analyzed specimens of the new species were identical, respectively; the 28S sequences differed from that of Liolope copulans Cohn, 1902 and from that of Harmotrema laticaudae Yamaguti, 1933 by 103 (8%) and 105 (8%) nucleotides, respectively. The 28S phylogenetic analysis recovered the new genus sister to a clade comprising L. copulans and H. laticaudae. A key to liolopid genera is provided herein. The present study comprises the first nucleotide-based phylogenetic placement of Harmotrema and first record of a liolopid from South Africa or Mozambique. It is the first proposal of a new liolopid genus in 43 yrs, and it documents a second liolopid genus from P. subniger while tripling the number of liolopid turtle hosts reported from the continent of Africa.

Molecular phylogenetic analysis of Neodiplostomum and Fibricola (Digenea, Diplostomidae) does not support host-based systematics

Fibricola and Neodiplostomum are diplostomid genera with very similar morphology that are currently separated based on their definitive hosts. Fibricola spp. are normally found in mammals, while Neodiplostomum spp. typically parasitize birds. Previously, no DNA sequence data was available for any member of Fibricola. We generated nuclear ribosomal and mtDNA sequences of Fibricola cratera (type-species), Fibricola lucidum and 6 species of Neodiplostomum. DNA sequences were used to examine phylogenetic interrelationships among Fibricola and Neodiplostomum and re-evaluate their systematics. Molecular phylogenies and morphological study suggest that Fibricola should be considered a junior synonym of Neodiplostomum. Therefore, we synonymize the two genera and transfer all members of Fibricola into Neodiplostomum. Specimens morphologically identified as Neodiplostomum cratera belonged to 3 distinct phylogenetic clades based on mitochondrial data. One of those clades also included sequences of specimens identified morphologically as Neodiplostomum lucidum. Further study is necessary to resolve the situation regarding the morphology of N. cratera. Our results demonstrated that some DNA sequences of N. americanum available in GenBank originate from misidentified Neodiplostomum banghami. Molecular phylogentic data revealed at least 2 independent host-switching events between avian and mammalian hosts in the evolutionary history of Neodiplostomum; however, the directionality of these host-switching events remains unclear.

The potential use of mitochondrial ribosomal genes (12S and 16S) in DNA barcoding and phylogenetic analysis of trematodes

Background

Genetic markers like the nuclear ribosomal RNA (rRNA) genes, internal transcribed spacer regions, mitochondrial protein-coding genes, and genomes have been utilized for molecular identification of parasitic trematodes. However, challenges such as the design of broadly applicable primers for the vast number of species within Digenea and the genetic markers’ ability to provide sufficient species-level resolution limited their utility. This study presented novel and broadly applicable primers using the mitochondrial 12S and 16S rRNA genes for Digenea and aimed to show their suitability as alternative genetic markers for molecular identification of orders Plagiorchiida, Echinostomida, and Strigeida.

Results

Our results revealed that the mitochondrial 12S and 16S rRNA genes are suitable for trematode molecular identification, with sufficient resolution to discriminate closely related species and achieve accurate species identification through phylogenetic placements. Moreover, the robustness of our newly designed primers to amplify medically important parasitic trematodes encompassing three orders was demonstrated through successful amplification. The convenience and applicability of the newly designed primers and adequate genetic variation of the mitochondrial rRNA genes can be useful as complementary markers for trematode molecular-based studies.

Conclusions

We demonstrated that the mitochondrial rRNA genes could be alternative genetic markers robust for trematode molecular identification and potentially helpful for DNA barcoding where our primers can be widely applied across the major Digenea orders. Furthermore, the potential of the mitochondrial rRNA genes for molecular systematics can be explored, enhancing their appeal for trematode molecular-based studies. The novelty of utilizing the mitochondrial rRNA genes and the designed primers in this study can potentially open avenues for species identification, discovery, and systematics in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08302-4.

Molecular phylogeny of Diplostomum, Tylodelphys, Austrodiplostomum and Paralaria (Digenea: Diplostomidae) necessitates systematic changes and reveals a history of evolutionary host switching events

The Diplostomidae Poirier, 1886 is a large, globally distributed family of digeneans parasitic in intestines of their definitive hosts. Diplostomum and Tylodelphys spp. are broadly distributed, commonly reported, and the most often sequenced diplostomid genera. The majority of published DNA sequences from these genera originated from larval stages only, which typically cannot be identified to the species level based on morphology alone. We generated partial large ribosomal subunit (28S) rRNA and cytochrome c oxidase subunit 1 (cox1) mtDNA gene sequences from 14 species/species-level lineages of Diplostomum, six species/species-level lineages of Tylodelphys, two species/species-level lineages of Austrodiplostomum, one species previously assigned to Paralaria, two species/species-level lineages of Dolichorchis and one unknown diplostomid. Our DNA sequences of 11 species/species-level lineages of Diplostomum (all identified to species), four species/species-level lineages of Tylodelphys (all identified to species), Austrodiplostomum compactum, Paralaria alarioides and Dolichorchis lacombeensis originated from adult specimens. 28S sequences were used for phylogenetic inference to demonstrate the position of Paralaria alarioides and Dolichorchis spp. within the Diplostomoidea and study the interrelationships of Diplostomum, Tylodelphys and Austrodiplostomum. Our results demonstrate that two diplostomids from the North American river otter (P. alarioides and a likely undescribed taxon) belong within Diplostomum. Further, our results demonstrate the non-monophyly of Tylodelphys due to the position of Austrodiplostomum spp., based on our phylogenetic analyses and morphology. Furthermore, the results of phylogenetic analysis of 28S confirmed the status of Dolichorchis as a separate genus. The phylogenies suggest multiple definitive host-switching events (birds to otters and among major avian groups) and a New World origin of Diplostomum and Tylodelphys spp. Our DNA sequences from adult digeneans revealed identities of 10 previously published lineages of Diplostomum and Tylodelphys, which were previously identified to genus only. The novel DNA data from this work provide opportunities for future comparisons of larval diplostomines collected in ecological studies.

Description of the Metacercaria of Cardiocephaloides sp. (Digenea, Diplostomoidea), Newly Recorded from the Brain of Gangetic Leaffish (Nandus nandus) and Its Genetic Characterization in India

PURPOSE

Cardiocephaloides comprises strigeid trematodes that represent a small genus. In this study, metacercaria identified as Cardiocephaloides sp. was collected from the Gangetic leaffish Nandus nandus from the Ganga River at Bairaj, Bijnor (29º01'N, 77º45'E) in the state of Uttar Pradesh (U.P.), India. Partial DNA sequences of the internal transcribed spacers (ITS1-5.8S-ITS2) and 28S gene of nuclear ribosomal DNA were generated and compared with available sequences of Cardiocephaloides species from Genbank database.

METHODS

Encysted metacercariae of Cardiocephaloides sp. were collected from Nandus nandus were processed, identified and documented using morphological methods. The ITS1-5.8S-ITS2 cluster and 28S gene of ribosomal DNA of metacercariae were also sequenced and used for phylogenetic analysis.

RESULTS

The infections of brain parasites are poorly understood in India and if studies are available, they are not properly described. During this study, the species collected were found belongs to the genus Cardiocephaloides. Metacercariae of Cardiocephaloides sp. is distinguished morphologically from others that also harbor brain by the presence of having an egg shape cyst and body elongate oval in shape with well-developed anterior part. The metacercariae are identified by matching of molecular sequence data and is compared to other species of Strigeidae.

CONCLUSION

This is the first record of metacercaria of Cardiocephaloides sp. from India. This molecular data from the present study will provide future comparative insights into species of Cardiocephaloides and its close affiliation to other congeners from different geographical areas.

Unravelling the diversity of the Crassiphialinae (Digenea: Diplostomidae) with molecular phylogeny and descriptions of five new species

Crassiphialinae Sudarikov, 1960 is a large subfamily of the Diplostomidae Poirier, 1886 with a complex taxonomic history. It includes a diversity of species parasitic in the intestines of avian and mammalian definitive hosts worldwide. Posthodiplostomum Dubois, 1936 is a large and broadly distributed crassiphialine genus notorious for its association with diseases in their fish second intermediate hosts. In this study, we generated partial 28S rDNA and cytochrome c oxidase subunit 1 (cox1) mtDNA gene sequences of digeneans belonging to seven crassiphialine genera. The 28S sequences were used to study the interrelationships among crassiphialines and their placement among other major diplostomoidean lineages. Our molecular phylogenetic analysis and review of morphology does not support subfamilies currently recognized in the Diplostomidae; therefore, we abandon the current subfamily system of the Diplostomidae. Molecular phylogenetic analyses suggest the synonymy of Posthodiplostomum, Ornithodiplostomum Dubois, 1936 and Mesoophorodiplostomum Dubois, 1936; morphological study of our well-fixed adult specimens and review of literature revealed lack of consistent differences among the three genera. Thus, we synonymize Ornithodiplostomum and Mesoophorodiplostomum with Posthodiplostomum. Our phylogenetic analyses suggest an Old World origin of Posthodiplostomum followed by multiple dispersal events among biogeographic realms. Furthermore, our analyses indicate that the ancestors of these digeneans likely parasitized ardeid definitive hosts. Four new species of Posthodiplostomum collected from birds in the New World as well as one new species of Posthodiplostomoides Williams, 1969 from Uganda are described.

Molecular and morphological evidence suggests the reallocation from Parastrigea brasiliana (Szidat, 1928) Dubois, 1964 to Apharyngostrigea Ciurea, 1927 (Digenea: Strigeidae), a parasite of boat-billed heron (Cochlearius cochlearius) from the Neotropical region

Parastrigea brasiliana (Szidat, 1928) Dubois, 1964, was described from (Cochlearius cochlearius) in South America. The taxonomy of this species has been unstable due that it was described as a member of Strigea Abildgaard, 1790. However, the same author one year later transferred it to Apharyngostrigea Ciurea, 1927 and since then, it has been alternatively placed in the genus Apharyngostrigea or Parastrigea Szidat, 1928 from Strigeidae. In the current research, specimens identified as P. brasiliana were collected from type host in southeastern Mexico. We sequenced three molecular markers: the internal transcribed spacers ITS1 and ITS2 including the 5.8S gene (ITS region), the D1-D3 domains of the large subunit (LSU) from nuclear DNA and cytochrome c oxidase subunit I (cox 1) from mitochondrial DNA. These sequences were aligned with other sequences available in the GenBank dataset from Strigeidae. Maximum likelihood and Bayesian analyses inferred with three molecular markers consistently showed that P. brasiliana is not closely related to other members of the genus Parastrigea and are placed in a reciprocal monophyletic clade inside Apharyngostrigea, with very low genetic divergence, varying from 0 to 0.09% for the ITS, from 0 to 0.08% for the LSU and from 0.21 to 0.43% for cox 1. Consequently, we proposed to reallocate it to A. brasiliana. The phylogenetic analyses obtained are key and very useful for re-evaluate the morphology of A. brasiliana because this species share morphological characters with the genera Parastrigea (concentration of vitelline follicles distributed in two lateral expansions on the forebody) and Apharyngostrigea (absence of pharynx). Finally, the current record of A. brasiliana expands its distribution range in four countries, namely, the USA, Mexico, Venezuela and Brazil, in the Neotropical region.

Morphological and molecular assessment of the diversity of trematode communities in freshwater gastropods and bivalves in Los Tuxtlas tropical rainforest

Trematode life cycles involve molluscs as first intermediate hosts. The identification of trematodes based on the morphology of cercariae released from molluscs is challenging because the identification relies on adult forms obtained from their definitive hosts. Several studies have recently genetically characterized these larval forms establishing a link with adults sampled from their vertebrate hosts, allowing their identification at species level. In Los Tuxtlas tropical rainforest, in south-eastern Mexico, 57 species of trematodes have been reported from wildlife vertebrates; however, studies evaluating the diversity of trematode cercariae in molluscs are lacking. Here, we studied 11 species of molluscs to assess the diversity of cercariae in two lakes of Los Tuxtlas, Veracruz, Mexico; six of the 11 species were infected. Twelve cercarial morphotypes were collected and characterized morphologically. Sequences of the 28S ribosomal RNA gene were generated to allocate each morphotype into a family using the most recent phylogenetic classification of the Digenea as a framework; molecular work revealed 16 genetic lineages; some cercariae were identified up to genus (Apharyngostrigea, Ascocotyle, Centrocestus, Echinochasmus, Lecithodendrium and Posthodiplostomum), and some to species levels (Gorgoderina rosamondae, Langeronia macrocirra, Oligogonotylus manteri and Phyllodistomum inecoli) based on their phylogenetic position within the tree, and the genetic distance with respect to other sequenced congeners. Therefore, the cercarial morphotypes in the present study represent at least 16 putative species. Our study contributes to a better understanding of the trematode diversity in an area of high vertebrate species diversity, and to the knowledge of trematode life cycles.

First Description of the Metacercaria of Nematostrigea serpens serpens (Nitzsch, 1819) (Trematoda, Strigeidae) and Phylogenetic Affiliation of Nematostrigea vietnamiensis Zhokhov & Mishina, 2011

BACKGROUND

The genus Nematostrigea comprises trematodes parasitising in fish-eating birds of Europe, Africa, and North America. Their life cycle is unknown.

PURPOSE

To provide the first description of metacercariae of Nematostrigea serpens serpens, a nominative subspecies of the type species of Nematostrigea, and to record metacercaria of Nematostrigea vietnamiensis, with molecular data.

METHODS

Encysted metacercariae of N. serpens serpens and N. vietnamiensis were collected from fish in Russia and Vietnam, respectively, and were processed, identified, and documented using standard morphological techniques. The 28S rRNA gene of metacercariae of both species and the cox1 gene of metacercariae an earlier studied adult of N. serpens serpens were sequenced and used for phylogenetic analysis.

RESULTS

Metacercaria of N. serpens serpens have a spatulate body with a foliate forebody and a short hindbody, two long lateral rectilinear pseudosuckers, and the holdfast organ with bifurcated anterior and entire posterior external lobes. The analysis of the cox1and 28S rRNA gene sequences unequivocally showed the conspecificity of metacercariae and adult stage of N. serpens serpens. Based on the 28S rRNA gene sequence-based phylogenetic analysis, the genus Nematostrigea is a sister taxon to the group of strigeid genera Cotylurus + Ichthyocotylurus. Morphological and phylogenetic data demonstrated that N. vietnamiensis does not belong to the genus Nematostrigea and is possibly be affiliated with the crassiphialine trematodes.

CONCLUSION

This is the first record of metacercariae of N. serpens serpens. N. vietnamiensis, renamed Prodiplostomulum vietnamiense comb. nov., must be moved to the crassiphialine 'Prodiplostomulum'-type metacercariae group.

Life cycle truncation in Digenea, a case study of Neophasis spp. (Acanthocolpidae)

Truncated life cycles may emerge in digeneans if the second intermediate host is eliminated, and the first intermediate host, the mollusc, takes up its role. To understand the causes of this type of life cycle truncation, we analyzed closely related species of the genus Neophasis (Acanthocolpidae) with three-host and two-host life cycles. The life cycle of Neophasis anarrhichae involves two hosts: wolffishes of the genus Anarhichas as the definitive host and the common whelk Buccinum undatum as the intermediate host. Neophasis oculata, a closely related species with a three-host life cycle, would be a suitable candidate for the comparison, but some previous data on its life cycle seem to be erroneous. In this study, we aimed to redescribe the life cycle of N. oculata and to verify the life cycle of N. anarrhichae using molecular and morphological methods. Putative life cycle stages of these two species from intermediate hosts were linked with adult worms from definitive hosts using ribosomal molecular data: 18S, ITS1, 5.8S-ITS2, 28S. These markers did not differ within the species and were only slightly different between them. Intra- and interspecific variability was also estimated using mitochondrial COI gene. In the constructed phylogeny Neophasis spp. formed a common clade with two other genera of the Acanthocolpidae, Tormopsolus and Pleorchis. We demonstrated that the first intermediate hosts of N. oculata were gastropods Neptunea despecta and B. undatum (Buccinoidea). Shorthorn sculpins Myoxocephalus scorpius were shown to act as the second intermediate and definitive hosts of N. oculata. The previous reconstruction of the two-host life cycle of N. anarrhichae was reaffirmed. We suggest that life cycle truncation in N. anarrhichae was initiated by an acquisition of continuous morphogenesis in the hermaphroditic generation and supported by a strong prey-predator relationship between A. lupus and B. undatum.

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Life cycles of digeneans Neophasis oculata and N. anarrhichae were redescribed.

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Phylogenetic position of genus Neophasis within family Acanthocolpidae was established.

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Causes of life cycle truncation within Neophasis are discussed.

Molecular and morphological characterisation of the metacercariae of two species of Cardiocephaloides (Digenea: Strigeidae) infecting endemic South African klipfish (Perciformes: Clinidae)

South African clinids are a major component of the temperate intertidal regions that are also known to participate in life cycles and transmission of several groups of parasites. However, the knowledge of trematode diversity of these fishes is incomplete. In this study, two species of Clinus Cuvier, the super klipfish Clinus superciliosus (Linnaeus) and the bluntnose klipfish Clinus cottoides Valenciennes, were collected from six localities along the South African coast and examined for the presence of trematodes. Metacercariae of Cardiocephaloides Sudarikov, 1959 were found in the eye vitreous humour and brain of C. superciliosus and in the eye vitreous humour of C. cottoides. Detailed analyses integrating morphological and molecular sequence data (28S rDNA, ITS2 rDNA-region, and COI mtDNA) revealed that these belong to two species, Cardiocephaloides physalis (Lutz, 1926) and an unknown species of Cardiocephaloides. This study provides the first report of clinid fishes serving as intermediate hosts for trematodes, reveals that the diversity of Cardiocephaloides in South Africa is higher than previously recorded, and highlights the need for further research to elucidate the life cycles of these trematode species. The broad geographical distribution of Cardiocephaloides spp. was confirmed in the present study based on molecular sequence data. The host-parasite interactions between clinid fishes and metacercariae of Cardiocephaloides are yet to be explored.

Intercontinental distributions, phylogenetic position and life cycles of species of Apharyngostrigea (Digenea, Diplostomoidea) illuminated with morphological, experimental, molecular and genomic data

When subjected to molecular study, species of digeneans believed to be cosmopolitan are usually found to consist of complexes of species with narrower distributions. We present molecular and morphological evidence of transcontinental distributions in two species of Apharyngostrigea Ciurea, 1924, based on samples from Africa and the Americas. Sequences of cytochrome c oxidase I and, in some samples, internal transcribed spacer, revealed Apharyngostrigea pipientis (Faust, 1918) in Tanzania (first known African record), Argentina, Brazil, USA and Canada. Sequences from A. pipientis also match previously published sequences identified as Apharyngostrigea cornu (Zeder, 1800) originating in Mexico. Hosts of A. pipientis surveyed include definitive hosts from the Afrotropic, Neotropic and Nearctic, as well as first and second intermediate hosts from the Americas, including the type host and type region. In addition, metacercariae of A. pipientis were obtained from experimentally infected Poecilia reticulata, the first known record of this parasite in a non-amphibian second intermediate host. Variation in cytochrome c oxidase I haplotypes in A. pipientis is consistent with a long established, wide-ranging species with moderate genetic structure among Nearctic, Neotropic and Afrotropic regions. We attribute this to natural dispersal by birds and find no evidence of anthropogenic introductions of exotic host species. Sequences of CO1 and ITS from adult Apharyngostrigea simplex (Johnston, 1904) from Egretta thula in Argentina matched published data from cercariae from Biomphalaria straminea from Brazil and metacercariae from Cnesterodon decemmaculatus in Argentina, consistent with previous morphological and life-cycle studies reporting this parasite-originally described in Australia-in South America. Analyses of the mitochondrial genome and rDNA operon from A. pipientis support prior phylogenies based on shorter markers showing the Strigeidae Railliet, 1919 to be polyphyletic.

Cryptic speciation among Tylodelphys spp.: the major helminth pathogens of fish and amphibians

Larvae of Tylodelphys Diesing, 1950 are major digenean pathogens of fish and amphibians. Tylodelphys spp. may induce mass mortality of fish and increase their susceptibility to predation. Even though Tylodelphys spp. cause substantial damage to aquaculture systems, surprisingly little is known regarding the taxonomy of this commercially important genus with a limited number of visible autapomorphic identification features. The authors obtained the DNA sequences and analyzed the molecular phylogenetics of Tylodelphys spp. adults isolated from bird hosts of Czech origin and provide comparative measurements of the analyzed species. They identified a previously unknown species complex that is subject to cryptic speciation and was previously morphologically identified as Tylodelphys excavata (Rudolphi, 1803) sensu lato. This species complex consists of three morphologically similar but genetically well-separated species. Tylodelphys excavata sensu stricto remains the dominant Tylodelphys isolated from Ciconia ciconia, which also serves as a satellite host of Tylodelphys circibuteonis Odening, 1962, which is the resurrected species for which birds of prey serve as core hosts. The authors describe Tylodelphys nigriciconis sp. n. Heneberg & Sitko as a new species identified in Ciconia nigra. By providing the first sequences of Tylodelphys podicipina Kozicka and Niewiadomska, 1960, they also show that Tylodelphys immer Dubois, 1961 is a junior synonym of T. podicipina. Further research is needed to match the provided molecular data with the DNA of larval Tylodelphys from outbreaks in commercially exploited fish species.

Phylogenetic position of Sphincterodiplostomum Dubois, 1936 (Digenea: Diplostomoidea) with description of a second species from Pantanal, Brazil

Sphincterodiplostomum is a monotypic genus of diplostomid digeneans that parasitize fish-eating birds in the neotropics. The type species Sphincterodiplostomum musculosum has a unique, dorsal, tubular invagination in the opisthosoma with a muscular sphincter. Whereas larvae of S. musculosum are relatively commonly reported in Neotropical fish helminth surveys, adult specimens from birds are rarely collected. Prior to our study, no DNA sequence data for S. musculosum were available. Our molecular and morphological study of mature and immature adult Sphincterodiplostomum specimens from three species of birds and one species of crocodilian revealed the presence of at least two species of Sphincterodiplostomum in the neotropics. We provide the first molecular phylogeny of the Diplostomoidea that includes Sphincterodiplostomum. In addition, this is the first record of S. musculosum from caimans, along with the first record of fully mature adult S. musculosum from green kingfisher Chloroceryle americana. The new species of Sphincterodiplostomum (Sphincterodiplostomum joaopinhoi n. sp.) can be morphologically distinguished from S. musculosum based on the anterior extent of vitelline follicles, narrower prosoma, substantially smaller holdfast organ and structure of tegumental spines. Our data revealed 0.7% interspecific divergence in 28S and 10.6-11.7% divergence in cox1 sequences between the two Sphincterodiplostomum species.

Leeches as the intermediate host for strigeid trematodes: genetic diversity and taxonomy of the genera Australapatemon Sudarikov, 1959 and Cotylurus Szidat, 1928

Background

Leeches (Hirudinida) play a significant role as intermediate hosts in the circulation of trematodes in the aquatic environment. However, species richness and the molecular diversity and phylogeny of larval stages of strigeid trematodes (tetracotyle) occurring in this group of aquatic invertebrates remain poorly understood. Here, we report our use of recently obtained sequences of several molecular markers to analyse some aspects of the ecology, taxonomy and phylogeny of the genera Australapatemon and Cotylurus, which utilise leeches as intermediate hosts.

Methods

From April 2017 to September 2018, 153 leeches were collected from several sampling stations in small rivers with slow-flowing waters and related drainage canals located in three regions of Poland. The distinctive forms of tetracotyle metacercariae collected from leeches supplemented with adult Strigeidae specimens sampled from a wide range of water birds were analysed using the 28S rDNA partial gene, the second internal transcribed spacer region (ITS2) region and the cytochrome c oxidase (COI) fragment.

Results

Among investigated leeches, metacercariae of the tetracotyle type were detected in the parenchyma and musculature of 62 specimens (prevalence 40.5%) with a mean intensity reaching 19.9 individuals. The taxonomic generic affiliation of metacercariae derived from the leeches revealed the occurrence of two strigeid genera: Australapatemon Sudarikov, 1959 and Cotylurus Szidat, 1928. Phylogenetic reconstructions based on the partial 28S rRNA gene, ITS2 region and partial COI gene confirmed the separation of the Australapatemon and Cotylurus clades. Taking currently available molecular data and our results into consideration, recently sequenced tetracotyle of Australapatemon represents most probably Au. minor; however, unclear phylogenetic relationships between Au. burti and Au. minor reduce the reliability of this conclusion. On the other hand, on the basis of the obtained sequences, supplemented with previously published data, the metacercariae of Cotylurus detected in leeches were identified as two species: C. strigeoides Dubois, 1958 and C. syrius Dubois, 1934. This is the first record of C. syrius from the intermediate host.

Conclusions

The results of this study suggest the separation of ecological niches and life cycles between C. cornutus (Rudolphi, 1808) and C. strigeoides/C. syrius, with potential serious evolutionary consequences for a wide range of host–parasite relationships. Moreover, phylogenetic analyses corroborated the polyphyletic character of C. syrius, the unclear status of C. cornutus and the separate position of Cotylurus raabei Bezubik, 1958 within Cotylurus. The data demonstrate the inconsistent taxonomic status of the sequenced tetracotyle of Australapatemon, resulting, in our opinion, from the limited availability of fully reliable, comparative sequences of related taxa in GenBank.

Phylogeny and systematics of the Proterodiplostomidae Dubois, 1936 (Digenea: Diplostomoidea) reflect the complex evolutionary history of the ancient digenean group

The Proterodiplostomidae Dubois, 1936 is a relatively small family of diplostomoidean digeneans parasitising the intestines of reptilian hosts associated with freshwater environments in tropical and subtropical regions. The greatest diversity of proterodiplostomids is found in crocodilians, although some parasitise snakes and turtles. According to the most recent revision, the Proterodiplostomidae included 17 genera within 5 subfamilies. Despite the complex taxonomic structure of the family, availability of testable morphology-based phylogenetic hypotheses and ancient hosts, molecular phylogenetic analyses of the group were practically lacking. Herein, we use novel DNA sequence data of the nuclear lsrRNA gene and mitochondrial cox1 gene from a broad range of proterodiplostomid taxa obtained from crocodilian, fish, and snake hosts on four continents to test the monophyly of the family and evaluate the present morphology-based classification system of the Proterodiplostomidae in comparison with the molecular phylogeny. This first detailed phylogeny for the Proterodiplostomidae challenges the current systematic framework. Combination of molecular phylogenetic data with examination of freshly collected quality specimens and re-evaluation of morphological criteria resulted in a number of systematic and nomenclatural changes along with a new phylogeny-based classification of the Proterodiplostomidae. As the result of our molecular and morphological analyses: (i) the current subfamily structure of the Proterodiplostomidae is abolished; (ii) three new genera, Paraproterodiplostomum n. g., Neocrocodilicola n. g. and Proteroduboisia n. g., are described and Pseudoneodiplostomoides Yamaguti, 1954 is restored and elevated from subgenus to genus level; (iii) two new species, Paraproterodiplostomum currani n. g., n. sp. and Archaeodiplostomum overstreeti n. sp., are described from the American alligator in Mississippi, USA. Comparison of the structure of terminal ducts of the reproductive system in all proterodiplostomid genera did not support the use of these structures for differentiation among subfamilies (or major clades) within the family, although they proved to be useful for distinguishing among genera and species. Our study includes the first report of proterodiplostomids from Australia and the first evidence of a snake acting as a paratenic host for a proterodiplostomid. A key to proterodiplostomid genera is provided. Questions of proterodiplostomid-host associations parasitic in crocodilians are discussed in connection with their historical biogeography. Our molecular phylogeny of the Proterodiplostomidae closely matches the current molecular phylogeny of crocodilians. Directions for future studies of the Proterodiplostomidae are outlined.

First elucidation of the life cycle in the family Brachycladiidae (Digenea), parasites of marine mammals

Digeneans of the family Brachycladiidae are cosmopolitan parasites restricted to marine mammals. Their life cycles are unknown. Phylogenetically, Brachycladiidae are closely related to Acanthocolpidae, parasites of marine teleost fishes. Acanthocolpida typically possess three-host life cycles with gastropods of the superfamily Buccinoidea acting as the first intermediate hosts for most species, and either fishes or bivalves acting as the second intermediate hosts. A few species previously identified as Neophasis differ from other Acanthocolpidae in having naticid gastropods as first intermediate hosts, and both fishes and bivalves as second ones. We assumed that this may indicate an incorrect life cycle description and revised previous data on rediae and cercariae of Neophasis spp. from Cryptonatica affinis (Naticidae) and metacercariae from cardiid bivalves at the White Sea using molecular and morphological approaches. Sequence comparison showed that rediae and cercariae from C. affinis resembling some representatives of the genus Neophasis and metacercariae from bivalves resembling Neophasis oculata belong to the brachycladiid species Orthosplanchnus arcticus. Thus, the life cycle of O. arcticus proceeds as follows: seals serve as the definitive host, C. affinis as the first intermediate host and cardiid bivalves as the second. We found one more type of redia and cercaria in C. affinis which, by molecular evidence, also belongs to Brachycladiidae and is closely related to O. arcticus. Here we refer to them as Brachycladiidae gen. sp. 1 WS. We suggest that Brachycladiidae gen. sp. 1 WS may belong to either Orthosplanchnus or Odhneriella, with beluga whales possibly being the definitive host. Morphological features of O. arcticus and Brachycladiidae gen. sp. 1 WS cercariae are summarised and matched with published data on putatively brachycladiid cercariae. We compare and discuss the diversity of life cycle patterns among Brachycladiidae and Acanthocolpidae, and show that they differ not only in the type of definitive host, but also in both intermediate hosts.

Phylogenetic Relationships of Cardiocephaloides spp. (Digenea, Diplostomoidea) and the Genetic Characterization of Cardiocephaloides physalis from Magellanic Penguin, Spheniscus magellanicus, in Chile

PURPOSE

Cardiocephaloides is a small genus of strigeid digeneans with an essentially cosmopolitan distribution. Most members of Cardiocephaloides are found in larid birds, however, Cardiocephaloides physalis is an exception and parasitizes penguins in some coastal regions of South America and South Africa. No prior molecular phylogenetic studies have included DNA sequence data of C. physalis. Herein, we provide molecular phylogenetic analyses of Cardiocephaloides using DNA sequences from five species of these strigeids.

METHODS

Adult Cardiocephaloides spp. were obtained from larid birds and penguins collected from 3 biogeographical realms (Palearctic, Nearctic and Neotropics). We have generated sequences of the complete ITS region and partial 28S gene of the nuclear ribosomal DNA, along with partial sequences of the mitochondrial CO1 gene for C. physalis, C. medioconiger and the type species of the genus, C. longicollis and used them for phylogenetic inference.

RESULTS

Cardiocephaloides spp. appeared as a 100% supported clade in the phylogenetic tree based on 28S sequences. The position of C. physalis varied between the phylogenetic trees based on the relatively conservative 28S gene on one hand, and variable ITS1 and COI sequences on the other. Cardiocephaloides physalis was nested within the clade of Cardiocephaloides spp. in the 28S tree and appeared as the sister group to the remaining members of the genus in the ITS1 region and COI trees. We detected 0.4-1.6% interspecific divergence in 28S, 1.9-6.9% in the ITS region and 8.7-11.8% in CO1 sequences of Cardiocephaloides spp. Our 28S sequence of C. physalis from South America and a shorter sequence from Africa available in the GenBank were identical.

CONCLUSION

Cardiocephaloides as represented in the currently available dataset is monophyletic with C. physalis parasitism in penguins likely resulting from a secondary host-switching event. Identical 28S sequences of C. physalis from South America and Africa cautiously confirm the broad distribution of this species, although comparison of faster mutating genes (e. g., CO1) is recommended for a better substantiated conclusion.

High diversity of metazoan parasites in carp gudgeons (Eleotridae: Hypseleotris spp.) from Eastern Australia

Knowledge of the parasite fauna of Australian freshwater fish is fragmentary and incomplete. An understanding of fish hosts and their associated parasites is vital for the successful management of aquatic ecosystems. In this study, we surveyed the parasite fauna of carp gudgeons (Hypseleotris spp.), a complex of species of Australian freshwater fishes, using morphology and molecular data for the 18S and 28S ribosomal RNA genes. We examined 137 individuals of three different taxa in the carp gudgeon species complex and found 16 parasitic taxa of the Digenea, Cestoda, Nematoda and Arthropoda (five adults and 11 larvae). Eleven parasites are reported for the first time from the carp gudgeons (Pseudodactylogyrus sp., Gyrodactylus sp., Clinostomum sp., Paradilepis patriciae, P. cf. kempi, two unidentified species of Paradilepis, Dendrouterina sp., Parvitaenia sp., two lineages of Cyclophyllidea gen. sp., Procamallanus sp., larvae of a spirurine nematode and Lernaea sp.), in addition to Apatemon cf. hypseleotris Negm-Eldin & Davies, 2001 and the invasive tapeworm Schyzocotyle acheilognathi (Yamaguti, 1934), which were previously reported from these fish hosts. Parasite species richness was double in Lake's and Midgley's carp gudgeons relative to western carp gudgeon. These findings highlight the key role of carp gudgeons as intermediate hosts for multiple parasites with complex life cycles using native birds as definitive hosts and the usefulness of DNA data for the identification of parasite larvae.