Nematode records and specimens from the South Australian Museum, Australian Museum, CSIRO Wildlife Collection, Queensland Museum, Western Australian Museum, and Natural History Museum, London, of 1107 individuals of Rattus fuscipes were examined. The nematode community comprised 19 families, 36 genera, and 44 identified species. Mastophorus muris and unidentified heligmonellids were recovered from 4 individuals of R. f. fuscipes. Rattus f. assimilis was infected with 40 identified species of nematode from 955 individuals; R. f. coracius 18 species from 107 individuals; and R. f. greyii 8 species from 28 individuals. Rattus fuscipes harboured 18 species in Northern Queensland, 27 species in Southern Queensland, 27 species in New South Wales, 19 species in Victoria, and 8 species in South Australia. A bootstrap analysis of the R. f. greyii nematode community indicated that 91.3% of species had been found. No core species were revealed. The Trichostrongylidae dominated with Nippostrongylus magnus, and Odilia emanuelae occurring in all the populations. Nippostrongylus magnus, 43% prevalence, in Victoria and Physaloptera troughtoni, 42% prevalence, in South Australia were secondary species. Sorensen’s indices indicated that R. f. assimilis and R. f. coracius had the most similar nematode communities, 54.8%. Overall, the Northern and Southern Queensland populations were most similar (77.3%) and the New South Wales and South Australian populations least similar (22.9%). The identifications of Heterakis spumosa, Physaloptera troughtoni, Rictularia mackerrasae, and Pterygodermatites pearsoni were confirmed. The species composition of the nematode community of R. fuscipes suggested a scenario of coevolution, host switching, recently acquired and occasional infections in a community of cosmopolitan, regional, and indigenous species. Species throughout the component communities of R. fuscipes indicated that climate and habitat were also determinants of species composition.

The nematode genus Rhabdias comprises over 100 species of parasitic nematodes that infect amphibians and reptiles, with a wide geographical distribution. To date, 25 species have been reported from the Neotropical region. Despite this diversity, few integrative studies, combining morphological and molecular data have been conducted to characterize species within the genus. Therefore, the main objective of the present study is to describe, through an integrative approach, a new species of Rhabdias found parasitizing the lungs of an anuran with a high concentration of skin toxins, Dendrobates tinctorius, from the Brazilian Amazon. The new species of Rhabdias is characterized by an elongated body, uniform cuticular inflation attenuated at the extremities, 4 submedian lips and 2 lateral lips, a cup-shaped buccal capsule, and an elongated tail. The morphology of the buccal capsule in Rhabdias camposi n. sp. is also unique among Rhabdias representatives, as this morphological character is known so far. Thus, we emphasize that a detailed study of this morphological trait for species of the genus will be crucial for species diagnosis. Molecular and phylogenetic analyses were performed using mitochondrial COI gene sequences. We observed that the new taxon is closely related to Rhabdias waiapi, a parasite of Pristimantis chiastonotus. Rhabdias camposi n. sp. represents the 26th species of the genus reported from the Neotropics in amphibians and the first described from a Dendrobates tinctorius host in Brazil.

We report the first identification of nematode parasitism in a nemertean host (Arctostemma arcticum), representing a novel host-parasite interaction in marine ecosystems. Larvae of the anisakid nematode were discovered within the rhynchocoel of A. arcticum collected from the White Sea, suggesting transmission via ingestion of infected crustaceans – a previously undocumented pathway. The nematode was identified as Phocanema bulbosum through both morphological and molecular analyses.

The presence of nematode in nemertean A. arcticum implies trophic transmission through nemertean predation on infected amphipods, supported by hoplonemertean feeding strategy. While some fish occasionally consume nemerteans, their low predation frequency suggests A. arcticum could act as a dead-end host.

This study expands the known host range of Anisakidae, though it remains uncertain whether nemerteans serve as competent hosts in the P. bulbosum life cycle. Nevertheless, the findings highlight the need to assess nemerteans’ potential influence on parasite dynamics in fisheries and aquaculture, particularly where they coexist with intermediate and definitive hosts.

Accurate characterization of helminth communities in amphibian hosts is essential for understanding host-parasite dynamics in changing environments. This study presents an integrative parasitological survey of Bufotes viridis populations in eastern Slovakia, using both morphological and molecular methods. A total of 61 road-killed individuals collected across 13 localities were examined for helminth presence. Only nematodes were detected, encompassing 3 families, Rhabdiasidae, Molineidae and Cosmocercidae. Four nematode species were recorded, Rhabdias rubrovenosa, Oswaldocruzia filiformis, O. ukrainae and Aplectana linstowi, and a further unidentified Cosmocerca species. Notably, R. rubrovenosa seems to be a new or previously misidentified helminth species found in Slovakia. Cosmocercidae represented the most abundant family, while Molineidae occurred scarcely. Each species was characterized genetically – for the members of Rhabdiasidae and Cosmocercidae, partial 18S rDNA, complete ITS1, complete 5.8S rRNA, complete ITS2 and partial 28S rDNA sequences were amplified, whereas for representatives of Molineidae, partial COI sequences were obtained. These results underscore the utility of combining molecular and morphological tools in helminth biodiversity studies and provide updated baseline data on nematode infections in B. viridis within an anthropogenically influenced landscape. Despite visual patterns indicating differences in the community compositions of nematode families between urban and rural localities, multivariate analyses testing revealed no significant differences.

Aprocta bainae Mutafchiev & Kinsella sp. nov, collected from the orbits of a flammulated owl, Psiloscops flammeolus (Kaup) (Strigiformes: Strigidae), from Montana, USA is described based on light and scanning electron microscopies. Additionally, fragments of 18S and 12S rRNA genes of the new species are provided. Based on the molecular data of the 18S gene, A. bainae n. sp. was included in a monophyletic clade of the genus Aprocta. Aprocta ophthalmophaga Stossich, 1902 and Aprocta colaptidis Schuurmans-Stekhoven, 1950 are considered species inquirendae. Aprocta colaptidis Schuurmans-Stekhoven, 1951, a homonym of A. colaptidis Schuurmans-Stekhoven, 1950, is considered a species incertae sedis.

The limestone and marlstone succession of the Pliensbachian Vale das Fontes and Lemede formations at the Global Boundary Stratotype Section and Point (GSSP) at Peniche (Portugal) received much attention in numerous studies. It contains abundant pyritic and limonitic aggregates, which are herein described and interpreted as remarkably preserved soft-bodied organisms (worms) for the first time. The slender to compact bodies with a cylindrical or dorsoventrally flattened cross-section are several centimetres long and have a diametre/width of 0.5–8 mm. They occur on bedding planes or are partly preserved within their burrows. Although their taphonomic history did not favour the preservation of many details, key features such as body shape, size and composition, as well as occasionally preserved segmentation and body appendages, allow a rough assignment to the phyla Nemertea, Annelida and Nematoda. Favourable circumstances such as intermittent dysoxic to anoxic bottom conditions, microbial activity and sudden burial have probably contributed to a reduced decay of the soft bodies. Comparison with similar successions globally shows that such a preservation of worms is not a unique process but occurs in several thick, fine-grained units throughout the Phanerozoic. Such inadequately preserved soft-bodied animals are still often overlooked but have the potential to add to our knowledge of the distribution and evolution of major clades of non-skeletal organisms.

Kalicephalus (Molin, 1861) comprises 33 species of gastrointestinal snake and lizard parasites with a cosmopolitan distribution, with seven taxa occurring in the Neotropical realm. In the present study, we describe Kalicephalus atroxi n. sp., found parasitising the snake Bothrops atrox, from the Eastern Amazon in the State of Amapá, North of Brazil. We used an integrative approach that included light microscopy, scanning electron microscopy, and sequencing of the internal transcribed spacer 1 (ITS1) region to describe Kalicephalus atroxi n. sp. The new species has a buccal capsule characteristic of the genus, a slight cuticular inflation in the cephalic region. The females have an amphidelphic reproductive system, a vulva with prominent lips, and a long tail, tapering posteriorly. The males have long and alate spicules, and the copulatory bursa is lobed with dorsal rays with distinct morphology compared to their congeners. Molecular analyses and phylogenetic reconstructions cluster the new species into a well-supported clade with K. costatus costatus, from Chironius fuscus, from the same locality in northern Brazil. Kalicephalus atroxi n. sp. is the eighth species of the genus in the Neotropics, the seventh in Brazil, the second described parasitising B. atrox in Brazil, and the first species of snake nematode described in the State of Amapá.

The Neotropical region is considered a biodiversity hotspot for reptiles, with eight families of terrestrial and freshwater chelonians. Parasites are of great importance to aquatic ecosystems and are essential to host communities. They help understand the patterns and phylogenetic relationships of their hosts and act to control populations. A literature survey on helminth parasites of chelonians in the Neotropical region was conducted, examining the most commonly found groups of helminths, the most parasitized hosts, compiling their biogeographical and political distribution and recording the parasite fauna of Phrynops geoffroanus in the state of Paraíba, northeastern Brazil. Considering the literature from 1850 to 2024, 202 helminth taxa were recorded. The Mesoamerican dominion had the highest number of helminth taxa, and Brazil was the political unit that recorded the most helminth taxa, followed by Mexico. Nematoda was the group with the highest number of taxa and occurred in all biogeographical units, with the species Spiroxys contortus being the most commonly found, followed by Trematoda, represented by the most commonly found species, Nematophila grandis. Hosts from the Chelidae family had the highest number of helminth taxa, followed by the Kinosternidae family. The most parasitized host species were Chelonoidis denticulatus and Phrynops hilarii. For the host Phrynops geoffroanus, the first occurrence of the nematode helminth Spiroxys contortus was recorded. This is the first study to include all parasitic helminths of terrestrial and freshwater chelonians in the Neotropical region, including a new occurrence in a chelonian host in the hinterland of Paraíba, Brazil.

Meteterakis striatura Oshmarin & Demshin, 1972 is redescribed from the posterior intestine of tropical tortoise Geoemyda spengleri (Gmelin, 1789) (Testudines: Geoemydidae) from China. Some characteristic features of the male reproductive system not reported previously are now reported for the present species. These include the presence of two blind diverticula near the mid-region of the seminal vesicle and a small cuticular structure near the opening of the cloaca – which we propose to name the ‘scutum.’ The morphological function and diagnostic value of these characters as well as presence of gubernaculum or ‘gubernacular mass’ in examined representatives of the genus, including paratype specimens of M. amamiensis Hasegawa, 1990 and M. ishikawanae Hasegawa, 1987 is discussed. Illustrative material is supplemented with scanning electron microscope and light microscope images of adult males and females. The molecular characterization of the species is inferred from 18S and 28S rDNA. The taxonomic composition of the genus Meteterakis is discussed and the full list of species with taxonomic remarks is updated.

Ascaridoidea (Nematoda) is a widespread superfamily of nematodes that comprises gastrointestinal parasites from all major groups of vertebrates. Although this taxon probably emerged in the Carboniferous, its Brazilian fossil record includes mostly eggs, found in ancient remains, collected in paleontological and archeological sites from the Mesozoic and Cenozoic Eras. The Tremembé Formation (Oligocene of the Taubaté Basin) has become an important source for paleoparasitological studies in avian coprolites during the third decade of the 21st century, with reports of eggs only at only a single cell stage, of embryonic development. Here we present the first egg of Ascaridoidea preserved containing morula, from a bird coprolite recovered from the shales of the Tremembé Formation. Three coprolites, from the outcrop of Aligra Comércio de Argila S/A, Taubaté municipality (State of São Paulo), were rehydrated and subjected to spontaneous sedimentation. Based on morphological and morphometric features and diet and zoopaleontological context, the trace fossils were assigned to piscivorous birds. The egg found showed morphological characteristics typical of Ascaridoidea: namely spherical form, ornamented, and somewhat thick shell. Moreover, this superfamily includes several taxa that infect piscivorous birds and fish in heteroxenous life cycles and produce eggs with similar features as the egg found in the present study. The paleoparasitological information associated with the paleofaunistic diversity of birds and fish from the Tremembé Formation, reveal that the ancient Brazilian paleoenvironments provided subsidies for the rise and success of nematodes infecting these animals during the Paleogene.

The dominant helminths infecting spiny mice (Acomys dimidiatus) in the montane wadis of the Sinai Peninsula of Egypt are spirurid nematodes, notably Protospirura muricola and Mastophorus muris. Both are relatively large robust stomach worms that accumulate in hosts resulting in high worm burdens. To ascertain whether the presence of spirurid worms or their burdens alters the host's likelihood of infection with other helminth species, we analysed a database containing quantitative data on helminth parasites of these mice (n = 431). This comprised of worm burdens recorded during 4 surveys, conducted at 4-year intervals, in 4 wadis, during late summer of each year. The presence of spirurid worms did not significantly alter species richness with other helminth species nor the likelihood of mice carrying other nematode species. However, there was a significant association, particularly of P. muricola, with the presence of intestinal stages of cestodes, and with the acanthocephalan Moniliformis acomysi. After controlling for intrinsic and extrinsic factors, mice harbouring spirurid worms had greater worm burdens of other helminths compared with mice without spirurids. Moreover, spirurid worm burdens showed a significant positive covariation with similarly adjusted species richness of other helminths, non-spirurid helminths, non-spirurid nematodes, oxyuroid nematodes and intestinal stage cestode worm burdens. We interpret these results as an indication that the key driver for co-occurrence of spirurids with other helminths is likely to be transmission via common arthropod hosts (for cestodes and acanthocephalans), but also that mice carrying the heavier spirurid worm burdens become more susceptible to directly transmitted nematodes such as the Oxyuroidea.

Six species of freshwater turtles dominate the Chaco-Pampa Plain in southern South America and their parasites have been relatively understudied, with most records concentrated in Brazil. Particularly in Argentina, there are only scattered records of parasites for most of the turtles that inhabit the region, leaving a large knowledge gap. The purpose of the present contribution is to increase the knowledge of the internal parasites of six species of freshwater turtles from Argentina, after 15 years of fieldwork, by providing new hosts and additional geographic records for many host-parasite relationships. Some molecular sequences of the studied parasites were provided as a tool for better species identification. We processed 433 stomach and fecal samples from live individuals and visceral and soft tissue samples from 54 dissected turtles collected from a wide range and different ecoregions. We found 6230 helminths belonging to 18 taxa (one cestode, 11 digeneans and six nematodes). Fourteen new parasite-host associations are reported here, and for the first time parasites are recorded for Phrynops williamsi. This work contributes significantly to the knowledge of the parasitofauna in freshwater turtles in Argentina, providing a detailed list of parasites present in each turtle species and reporting molecular characters for future studies.

The Australasian harrier Circus approximans, a native of Australia, New Zealand and the South Pacific, is an opportunistic hunter of small prey, although a large part of its diet consists of carrion, mainly from roadkill. Besides a record of a single, unnamed species of capillariid nematode there have been no investigations into the parasites of Australasian harriers in New Zealand. In this study, a helminthological survey of sixty-five deceased harriers from southern New Zealand uncovered a gastrointestinal helminth fauna consisting of six parasite species. Porrocaecum circinum (Nematoda) was previously described only from fragmented females, and a redescription is presented here. Procyrnea fraseri n. sp. (Nematoda) is described, and distinguished from its congeners by its slender body shape and shorter spicules. Strigea falconis (Trematoda) is reported for the first time in New Zealand. Cladotaenia anomalis (Cestoda) and Polymorphus circi (Acanthocephala) were previously described as new species elsewhere. An unnamed species of capillariid appears to be mainly confined to North Island and is rare in South Island. Prevalence and intensity metrics are given, and DNA sequences provided to accompany new re/descriptions. Potential intermediate hosts are discussed, and the origins of the helminths and their potential for pathogenicity are considered.

Cyathostoma lari is a parasite of the nasal and orbital sinuses of gulls and other hosts in Europe and Canada. Here, we provide an overview of previously published data on the prevalence and infection intensity of C. lari in gulls. Furthermore, based on our data, we analyze the spatiotemporal trends in the prevalence and intensity of infection by C. lari in Chroicocephalus ridibundus in Czechia (central Europe; data from 1964 to 2014) and compare them with those obtained from five species of gulls in Karelia (Northwest Russia; data from 2012–2020). Based on our preliminary observations, we hypothesized that C. lari is subject to a decline in certain regions, but this decline is not necessarily applicable throughout its distribution range. We found that the C. lari population crashed in specific parts of its distribution range. The reasons are unknown, but the observed population changes correspond with the diet switch of their core host in Czechia, C. ridibundus. We previously observed a diet switch in Czech C. ridibundus from earthworms (intermediate hosts of C. lari) to other types of food. This diet switch affected both young and adult birds. Nevertheless, it may not necessarily affect populations in other regions, where they depend less on earthworms collected from agrocenoses affected by agrochemicals and trampling. Correspondingly, we found that these changes were limited only to regions where the gulls feed (or fed) on arable fields. In Karelia, where arable fields are scarce, gulls likely continue to feed on earthworms and still display high infection rates by C. lari. Therefore, C. lari, a parasite of the nasal and orbital sinuses of gulls, nearly disappeared from their central European nesting grounds but is still present in better-preserved parts of its distribution range.

The present study investigated the horizontal and vertical distribution of meiofauna community and Nematoda assemblages on two sandy beaches and two muddy tidal flats in a freshwater Amazon estuary governed by mesotides. Meiofauna density was significantly higher in muddy environments, explained by the higher food availability. On the one hand, there was no difference between sediment layers in both sandy environments, which suggests that individuals must have migrated to layers deeper than 10 cm. On the other, the highest densities and richness in muddy environments occurred in the upper layer due to higher food and oxygen availability in the surface sediment layer, which decreases with depth. Muddy environments differed on both beaches; they had the highest nematode genera densities and richness. This might be explained by the high nutrient enrichment in these environments. There was no significant difference in Nematoda density and richness between zones in any environment, likely due to the small mid-littoral extension (<40 m), which did not favour the high spatial variability of genera. Nematoda density was higher at a depth of 0–2 cm in both muddy environments, explained by the availability of oxygen and food. The high abundance of deposit-feeder genera in muddy environments indicates high organic enrichment, whereas the distribution of trophic types was more homogeneous on the beaches where abiotic factors tended to be more structuring than food availability.

Two new species of Microlaimidae: Microlaimus paraaffinis sp. nov. and Pseudomicrolaimus major sp. nov. are described from Yangma Island, the Yellow Sea. M. paraaffinis sp. nov. is characterized by body length 662–785 μm, six inner and six outer labial sensilla papilliform, four short cephalic setae 3–4 μm in length, amphidial fovea cryptocircular at level of buccal cavity, spicules L-shaped with equal thickness, gubernaculum boat shaped, tail conico-cylindrical with short cylindrical portion. P. major sp. nov. is characterized by large body size, six inner labial sensilla papilliform, six outer labial sensilla and four cephalic sensilla setiform, eight subcephalic setae present, amphidial fovea cryptospiral, anterior pharynx region at the buccal cavity widened, posterior pharynx region with oval-shaped bulb, spicules curved with proximal portion enlarged, gubernaculum boat shaped, tail short and conical. Pictorial key to genus Pseudomicrolaimus is given.

Marmosa constantiae is a species of marsupial restricted to the central portion of South America. In Brazil, it occurs in the northwestern region including five states of the Amazon, Cerrado, and Pantanal biomes. However, there is no study of the helminth fauna or helminth community structure for this marsupial. The aims of this study were to describe the species composition and to analyse the structure of the helminthic community of M. constantiae in an area of the Amazon Arc in Sinop, north of the state of Mato Grosso, Brazil. Parasites were searched in 53 specimens of this marsupial, among which 44 were infected with at least one helminth species. Parasitic helminths were counted and identified. Nine species were collected: seven nematodes, one cestode, and one acanthocephalan. The most abundant species were Gracilioxyuris agilisis, Travassostrongylus scheibelorum, Pterygodermatites sinopiensis, and Subulura eliseae. These species were the only dominant ones in the component community. No significant differences were observed in the abundance and prevalence of helminths between male and female hosts. Host body size significantly influenced helminth abundance in males. The pattern of community structure considering the infracommunities in this locality indicated more species replacement than species loss along the environmental gradient. This is the first study to report the helminth fauna and the helminth community structure of M. constantiae.

The spirurid nematode Thubunaea schukurovi Annaev, 1973 (Physalopteridae) is redescribed by means of light microscopy and scanning electron microscopy from Ablepharus chernovi collected in Çamlıyayla, Turkey. This is the first record of the species from this host and the first record of the genus Thubunaea from Turkey. The taxonomic status of the species of the genus Thubunaea from the Palaeacrtic and Indomalayan realms is reviewed based on their original morphological descriptions; as a result, Thubunaea dessetae Barus & Tenora, 1976, a parasite of Saara hardwickii (Gray) (Agamidae) in Afghanistan, is transferred to the genus Pseudabbreviata as Pseudabbreviata dessetae (Barus & Tenora, 1976) n. comb. Several species described in India, that is, Thubunaea singhi Deshmukh, 1969 and Thubunaea brooki Deshmukh, 1969, both from Hemidactylus brookii Gray (Gekkonidae), and Thubunaea aurangabadensis Deshmukh, 1969 and Thubunaea syedi Deshmukh, 1969, both from Hemidactylus giganteus Stoliczka, are considered members of the genus Physalopteroides; therefore, the following new combinations are proposed: Physalopteroides singhi, Physalopteroides brooki, Physalopteroides aurangabadensis and Physalopteroides syedi. Thubunaea hemidactylae Oshmarin & Demshin, 1972 from Hemidactylus frenatus Duméril & Bibron in Vietnam is considered a member of the genus Physalopteroides as P. hemidactylae (Oshmarin & Demshin, 1972) n. comb.

A new species of Ancyracanthus, parasite of the electric eel Electrophorus varii, in the Brazilian Amazon, is described based on morphological and molecular characterization. Ancyracanthus electrophori n. sp. differs from the two congeners namely, Ancyracanthus pinnatifidus and Ancyracanthus schubarti, based on the structure of cephalic appendages, number and arrangement of caudal papillae in males, vulva very close to anus in females, eggs with smoothly mamillated shell, host taxon and geographical origin. Moreover, the new species is the first in the genus to be described with thorny cuticular rings and to be observed with the use of scanning electron microscopy (SEM). The morphology of A. pinnatifidus and A. schubarti is still poorly-known and should be revised in details; however, the separation between them and the new species was clear. Genetic characterization based on 28S rDNA and cytochrome c oxidase subunit I (cox1) mtDNA partial sequences, performed for the first time in Acyracanthus, along with phylogenetic reconstructions using both genetic markers, placed Ancyracanthus electrophori n. sp. in a suggestive basal position within Gnathostomatidae. Phylogenetic reconstructions using cox1 sequences also suggested lack of monophyly in the genera Gnathostoma and Spiroxys and, consequently, in the subfamilies Gnathostominae and Spiroxyinae. However, such results are preliminary. With the first genetic characterization and observations using SEM in Ancyracanthus, resulting in the discovery of a new species and in the expansion of the geographical occurrence of the genus to Amazonian fish, an important step towards a better understanding of these nematodes has been taken.

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.