Morrittospora corbiculae n. gen. n. sp., a microsporidian parasite infecting the invasive Asian clam Corbicula fluminea from the River Thames, London

Microsporidia are highly diverse parasites of a broad range of eukaryotic hosts in both aquatic and terrestrial ecosystems. Freshwater diversity of microsporidia and their associations with bivalves is understudied, particularly in invasive non-native hosts. In this study we use molecular methods complemented by histopathology and transmission electron microscopy to screen native and invasive bivalve species from the River Thames for the presence of microsporidia. We reveal a novel microsporidian parasite infecting the invasive Asian clam Corbicula fluminea at a high prevalence, described in this manuscript as Morrittospora corbiculae n. gen. n. sp. Histopathology showed this parasite infects epithelial cells of C. fluminea digestive gland. Molecular and histopathology investigation also demonstrated potential spillover of infection to other co-habiting bivalve species in the River Thames. We place the newly described microsporidian lineage in a phylogenetic context and discuss the potential implications of microsporidian parasites in the spread of invasive non-native species.