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Cercariae, the free-living larval stages of trematodes, have adopted an amazing variety of transmission strategies. One of them is prey-mimetism, i.e. cercariae mimicking prey to attract motile hosts to be eaten. In a period between 2002 and 2019, we examined small planorbid snails, Bathyomphalus contortus, Gyraulus parvus and Planorbis planorbis from lakes in Finland and Iceland and from the Curonian Lagoon in Lithuania. Cercariae with conspicuously enlarged tails and unusual swimming behaviour, likely mimicking invertebrate prey, were detected and studied by the use of morphological and molecular (cox1, ITS1-5.8S-ITS2 and 28S rDNA) methods. Cercariae of two species belonging to the genus Apatemon (Strigeidae) were recognised. We consider Apatemon sp. 5 ex P. planorbis from the Curonian Lagoon identical to Cercaria globocaudata U. Szidat, 1940. Cercariae ex G. parvus from Iceland and ex B. contortus from Finland were conspecific, and we named them Apatemon sp. 6; these cercariae could not be associated with any known species. For the first time, we verified that cercariae of the Bulbocauda group belong to the genus Apatemon. We provide a mini-review on records of furcocercariae of the family Strigeidae with enlarged tails reported in freshwaters of the northern hemisphere and reveal that it is not only Apatemon but also Australapatemon and most likely Strigea which belong to the Bulbocauda group, rendering it a purely ecological assemblage. Understanding which invertebrate swimming behaviour these cercariae are mimicking will enhance our knowledge of the processes behind trematode transmission and will help to assess evolutionary pathways of host-finding strategies in trematodes. [ABSTRACT FROM AUTHOR]

Parasites are important components of ecosystems, thus identifying patterns of their diversity is crucial for studies investigating ecosystem functioning, food web structure, trophic interactions and epidemiological parameters. Via an integrative taxonomic approach, we studied the diversity and distribution of trematodes of the genus Plagiorchis Lühe, 1899 in snails in the sub‐Arctic freshwater ecosystems of Iceland and for comparative purposes in West and North Europe (Ireland and Finland, respectively), supplemented by data from Alaska, USA, all regions with remarkably few data on trematode diversity. Molecular genetic and morphological analyses of 68 samples of cercarial isolates of Plagiorchis collected from 3,069 snails belonging to six species revealed a total of 16 species/species‐level lineages of Plagiorchis with five found in Iceland, six in Finland, nine in Ireland and five in Alaska. Two species‐level lineages found in Iceland, Finland and Ireland were reported for the first time; for all species/species‐level lineages identified by DNA sequences we provide the first morphological characterization. Our analysis of the diversity of Plagiorchis and their snail host spectrum in Europe provides evidence for Radix balthica and Lymnaea stagnalis as primary first intermediate hosts. By comparing DNA sequence data for Plagiorchis spp. from this and previous studies, we demonstrate no overlapping spatial distribution for members of the genus in our material between the continents of Europe and North America. We infer that the spatial distribution of Plagiorchis spp. is constrained mainly by migratory birds' ranges. Finally, in Europe, further research is needed to evaluate whether the diversity of Plagiorchis spp. in R. balthica is unique to high latitude ecosystems. [ABSTRACT FROM AUTHOR]