Description of a new <i>Klossia</i> species (Apicomplexa; Adeleorina; Adeleidae) in Canada from an introduced European land snail (<i>Trochulus hispidus</i>), with a discussion on the taxonomy of the family Adeleidae Mesnil, 1903

European native land snails, Trochulus hispidus (Linnaeus, 1758), were collected from Brighton, Ontario, Canada, over a 20-month period beginning in April 2020. Polysporocystic oocysts consistent with Klossia spp. (Apicomplexa: Adeleidae) were observed in macerated snail kidney tissues by light microscopy. Sporulated oocysts measured 103 ± 5.8 µm × 99 ± 7.4 µm with indistinct or absent oocyst residuum; oocysts contained more than 125 tetrazoic sporocysts. Sporocysts measured 12 ± 0.66 µm × 11 ± 0.76 µm with a centrally placed sporocyst residuum and a few irregularly dispersed granules. DNA was extracted from all kidney tissues and prevalence of the Klossia-infection determined by Klossia-specific PCR was 46% (19 of 41). Nuclear 18S rDNA (1800 bp) and complete mitochondrial genome (6757 bp) sequences differed sufficiently from available Klossia spp. sequences to justify description of a new Klossia species, Klossia vaderbriani n. sp. Phylogenetic analysis using combined nuclear (18S rDNA) and mitochondrial (cytochrome c oxidase subunit I—COI) sequences strongly support the monophyly of the genus Klossia but not of the family Adeleidae to which these parasites belong. These observations and a detailed literature review supported a wider discussion on the taxonomy of the genera in the family Adeleidae.