We describe the marine horsehair worm Nectonema shimadai sp. nov., which was parasitic in a snapping shrimp (Alpheus sp.) collected at 4 m depth from the coastal water of Kikaijima Island, Japan, northwestern Pacific. The nematomorph was a female, 49 mm in length and 340 μm in width, salmon-pink when alive, with a translucent anterior body region and a distinct anterior chamber. The 18S sequence from N. shimadai sp. nov. was 12.8%, 9.8%, 9.6%, and 9.3% divergent in Kimura 2-parametar (K2P) distance from Nectonema sp. parasitic in the isopod Natatolana japonensis, Nectonema sp. parasitic in the crab Chionoecetes bairdi, N. munidae, and N. agile, respectively. In an 18S tree, N. shimadai sp. nov. was the sister taxon to a clade comprising three decapod-parasitic species, and species sharing the same host group or ocean were not monophyletic. The tree may reflect genetically distant warm- and cold-water lineages within decapod-parasitic nematomorphs.

Seabirds are largely used as indicators of Ocean health and are final hosts of several helminth parasites. However, the helminth fauna of seabirds is still poorly studied. Here, we quantified the diversity of gastrointestinal parasites in 52 individuals belonging to 10 seabird species with different habitat preferences and feeding strategies from the North-East Atlantic and Antarctica. Fresh carcasses were collected in Northern France and at Svarthamaren (Dronning Maud Land, Antarctica), helminth parasites were extracted from the gastrointestinal tract, and were identified by morphological inspection and DNA barcoding. In total, we identified 13 helminth taxa. North-East Atlantic seabirds hosted parasites from four helminth groups (Acanthocephala, Cestoda, Nematoda, Trematoda), while Antarctic seabirds hosted Acanthocephala and Cestoda only. The largest parasite diversity was found in northern fulmars Fulmarus glacialis (9 species), European shags Gulosus aristotelis (5 species), razorbills Alca torda (4 species), and black-legged kittiwakes Rissa tridactyla (4 species). Co-infections with multiple parasite species in single hosts were common. Oceanic diving species were found to be the most parasite-poor, with common guillemots Uria aalge and Atlantic puffins Fratercula arctica hosting no parasites. In contrast, oceanic surface-feeding seabirds had a large parasite diversity, which notably included trematodes, and was comparable to that of coastal species. To the best of our knowledge, this study identified 9 new host-parasite associations: Andracantha sp. in northern fulmars and south polar skuas Stercorarius maccormicki, C. septentrionale in northern fulmars and black-legged kittiwakes, a species of Microphallidae in black-legged kittiwakes, Cardiocephaloides longicollis in European shags, Cryptocotyle lingua in Sandwich terns Thalasseus sandvicensis, and a clophyllidean species in south polar skuas and Antarctic petrels Thalassoica antarctica.

Limpets are abundant and ecologically important gastropods in intertidal and some riverine ecosystems, yet their role in trematode transmission remains comparatively understudied. We investigated trematode infection in intertidal limpets from Otago Harbour, New Zealand, using a molecular approach. Two species were identified: the avian schistosome Gigantobilharzia cf. patagonensis in Siphonaria australis and Acanthoparyphium sp. A metacercariae in Notoacmea sp. Gigantobilharzia cf. patagonensis was detected at all five sampling sites, with prevalence ranging from 2.6% to 100%. Haplotype network analysis using cox1 revealed high haplotype diversity and a star-like topology, suggesting a recent population expansion. This study expanded the known diversity of marine schistosomes in the region and raises potential public health concerns with cercarial dermatitis. We also conducted a literature synthesis further demonstrating that limpets contribute to trematode transmission across 12 superfamilies and 23 families, with distinct parasitism profiles between freshwater and marine environments. These findings highlight limpets as overlooked but significant hosts in trematode ecology and emphasize the need for broader surveys and definitive host screening to resolve incomplete life cycles and assess epidemiological risks in coastal ecosystems.

Terrestrial isopods (Isopoda: Oniscidea), also known as sowbugs or woodlice, are one of the few groups of crustaceans with fully terrestrial members. Sowbugs are readily transported by human activity, with many species having been introduced worldwide. Although nonnative sowbugs have been present in Canada for more than 150 years, the study of sowbugs in Canada has been largely overlooked, especially in the Prairie Provinces. We conducted the first survey of sowbug species in Alberta, with additional collections from British Columbia, Saskatchewan, Ontario, and Newfoundland. We compiled an updated Canadian species checklist of 32 species from 12 families, including seven new species records for Canada since the previous 2001 checklist. Species with older records tend to occupy more provinces than species recorded more recently. Nine sowbug species occur in Alberta: all are nonnative and originate from Europe or Asia. Our collection of Nagurus cristatus (Dollfus, 1899) (Trachelipodidae) from Edmonton represents the first record from Canada. We support our identifications with molecular data (cytochrome c oxidase subunit 1 barcode region). Further surveys of sowbugs in the Prairie Provinces may uncover additional species; we encourage reporting of sowbug bycatch from arthropod surveys and note the utility of community science platforms for conducting sowbug surveys.

Several Monochamus species (Coleoptera: Cerambycidae) use monochamol as an aggregation-sex pheromone, raising questions about how they maintain reproductive isolation. Herbivorous insects use host plant semiochemicals as cues for mate location and, with or without habitat cues, these could confer reproductive isolation among sympatric Monochamus spp. To test this hypothesis, host and habitat preferences in mate location were examined for sympatric populations of Monochamus maculosus, Monochamus notatus, and Monochamus scutellatus in the Algoma District, Ontario, Canada. Field experiments were performed to investigate whether differences in host preference, vertical distribution across the forest canopy, spatial distribution within down and standing dead trees, or any combination of these factors could minimise cross-attraction to monochamol. Results showed that more M. maculosus were attracted to monochamol combined with jack pine foliage than with balsam fir or white spruce, whereas no differences in host attractivity were observed for the other species. Vertical abundance of M. maculosus and M. scutellatus was similar across forests. Spatial distribution provided limited evidence for species segregation within hosts. No evidence was found that host or habitat preferences contribute to reproductive isolation in M. maculosus, M. notatus, or M. scutellatus, suggesting that vertical distribution could be driven by resource availability.

The diversity of Rhabdias includes 101 species, 71 of which parasitize the lungs of anurans, caudates, gymnophionans, and some occur in reptiles worldwide. Currently, 26 species are found in the Neotropical region, and in Brazil, there are 16 nominal species, a relatively low number considering the high diversity of potential hosts. Here, we describe a new species of Rhabdias found in Physalaemus albonotatus, with morphological and molecular data, as well as phylogenetic analyses using sequences of the mitochondrial gene Cytochrome Oxidase Subunit I (COI). Rhabdias taquariensis n. sp. differs from other known species by a set of morphometric traits and by presenting a well-defined internal shape of the cephalic dilation. Molecular analyses revealed that R. taquariensis n. sp. exhibits a significant divergence of 13.6% in COI compared to the Rhabdias cf. stenocephala species complex. Additionally, phylogenetic reconstructions indicate that the new species represents a distinct lineage, external to a clade formed by species such as Rhabdias fuelleborni, Rhabdias cf. stenocephala, and Rhabdias waiapi. Rhabdias taquariensis n. sp. is the 27th species described in the Neotropical region and the 16th in Brazil, the first description of a species of the genus Rhabdias for Physalaemus albonotatus, and one of the few Rhabdias species described for the Cerrado biome.

Acanthobothrium represents the most species-rich genus of onchoproteocephalidean cestodes, with adults parasitizing the spiral valves of elasmobranch fishes. Between October 2023 and August 2025, Acanthobothrium minus, previously reported from the Algerian coast in Raja asterias (Mediterranean starry ray), was collected from the spiral valve of Raja asterias, and the rough ray, Raja radula. This parasite is characterized by its small body size and reduced number of proglottids. In this study, we examine its host specificity and provide a redescription of A. minus from the type locality and host, and an additional host (R. radula) using light microscopy and molecular approaches. Furthermore, we present, for the first time, molecular and phylogenetic data based on 28S rDNA sequences for this species, along with a detailed morphometric comparison to other CategoryII Acanthobothrium species infecting Rajidae from the Mediterranean. Our phylogenetic results show all Acanthobothrium species 28S sequences from the Mediterannean grouping in the same clade and suggest close affinity with Acanthobothrium coronatum (Category 4). These results support that these taxonomic categories are a useful guide for morphological comparisons but are not correlated with true phylogenetic relationships. Furthermore, the regional grouping of these sequences from relatively distantly related definitive hosts (the shark Scyliorhinus stellaris L. and the skates R. asterias and R. radula) supports evolution of this elasmobranch-Acanthobothrium association in the Mediterranean through host switching due to shared ecological features of the hosts followed by speciation by isolation. However, additional support for this hypothesis would require more in-depth taxonomic representation of available sequence data.

Many parasitic nematodes exhibit a range of behavioural responses to host-associated stimuli, especially chemicals. The infective juveniles (IJs) of specialized insect-infecting nematodes, i.e., entomopathogenic nematodes (EPNs), can show directed movement (taxis) or other behaviours in response to odorants. However, relatively little is known in terms of IJ responses in the context of increases in non-directed movement (kinesis) resulting from physical contact with host chemicals, or the effects of insect semiochemicals on EPN behaviours. We individually exposed IJs of the EPN Steinernema carpocapsae to solutions representing five different treatments, including those containing the macerated tissues of a suitable insect host (greater wax moth larvae – waxworms) or a semiochemical (1-pentadecene) secreted by various insects. We conducted behavioural observations at six time points over an 8-h period, measuring the total number of movements by each IJ (orthokinesis), along with the occurrence of side-to-side movements (klinokinesis) or head-waving. We found that IJs in the waxworm or 1-pentadecene solutions showed high levels of overall movement, but waxworm-exposed IJs also exhibited the most sinusoidal movement, whereas IJs exposed to 1-pentadecene exhibited far more head-waving than nematodes in the other treatments. These results indicate that S. carpocapsae shows behavioural responses through kinesis when exposed to host chemical cues in an aqueous medium. As our study is only the second report of EPNs responding to an insect semiochemical, this is a promising area for future studies to better understand host-finding strategies by these nematodes, with possible applications for their use in insect biocontrol.