Trematode species diversity in the faucet snail, Bithynia tentaculata at the western edge of its native distribution, in Ireland

Trematodes and their snail hosts have developed intimate parasite-host associations, with snails supporting a diverse and often species-specific trematode fauna. In the faucet snail, Bithynia tentaculata (Caenogastropoda, Littorinimorpha), a unique trematode fauna has been recorded recently. However, knowledge of the exact species identity, phylogenetic relationships, and geographical distribution remains limited as many of the species belong to groups with unclear or controversial taxonomical assignment. To contribute to our knowledge of the trematodes, we investigated the trematode fauna of B. tentaculata by examining a total of 556 snails from lakes in County Galway, Ireland. Using an integrative taxonomic approach including DNA sequence data analyses (28S rRNA gene, ITS1-5.8S-ITS2, ITS2, cox1, nad1) and morphological tools (taxonomical drawings and measurements), we identified nine trematode species of seven families, with seven species occurring as cercariae (Cyathocotyle prussica, Lecithodendrium linstowi, Lecithodendrium sp., Asymphylodora progenetica, Sphaerostoma bramae, Metorchis xanthosomus, and Notocotylus sp.) and three species occurring as metacercariae (A. progenetica, Parasymphylodora parasquamosa, and Sphaeridiotrema sp.). Except for S. bramae, all are new species records for Ireland and provide the most western distribution of these trematodes in Europe. The trematode species recorded are known to use a wide range of definitive hosts and have a wide geographical distribution; among them are species members of genera that are zoonotic (Metorchis) and pathogenic to wildlife (Cyathocotyle, Sphaeridiotrema, and Notocotylus). There remains an ongoing need for precise identification of the trematode species to ensure that wider ecological contexts are correctly understood and biodiversity and disease threats can be accurately evaluated.