An alien and invasive species of freshwater mussel <i>Sinanodonta woodiana</i> (Lea, 1834) asscociated with the parasitic species of water mite <i>Unionicola ypsilophora</i> (Bonz, 1783)

The article presents the results of research on water mites, namely Unionicola (Unionicola) ypsilophora (Bonz, 1783) (Arthropoda: Acari: Unionicolidae), associated with freshwater mussels (Mollusca: Bivalvia: Unionidae) in Poland. The mussels included Sinanodonta woodiana (Lea, 1834), Anodonta cygnea (Linnaeus, 1758) and Anodonta anatina (Linnaeus, 1758). Sinanodonta woodiana (62%) was the most numerous in the collected material, followed by Anodonta anatina (22%) and Anodonta cygnea (16%). Gill mites, U. ypsilophora, were found in A. cygnea and S. woodiana and absent in A. anatina. These mites showed preferences in the choice of host: A. cygnea was the most frequently preferred (prevalence = 100%, intensity = 7–9), while the alien and invasive mussel, S. woodiana, was less frequently preferred (prevalence = 14.6%, intensity = 1–3). The mussels were found in fish ponds near Milicz, Lower Silesia, Poland. Associations in the collections with S. woodiana were considered “vagrant” associations; however, further study may reveal additional aspects of the nature of these associations, should they be routinely found and further detailed. This is a rare report of this type in the literature on the subject, which sheds new light on the problem of adaptation of the parasite to an alien species of mussel. Unionicola ypsilophora were more likely to inhabit larger and older specimens, in both S. woodiana and A. cygnea populations.