First report of endosymbionts in Dreissena polymorpha from Sweden.
We report the first results of parasitological study of Dreissena polymorpha (zebra mussels) from Sweden. The samples of Dreissena were collected from Lake Erken in July 2007. The most common endosymbionts found in the mantle cavity of the mussels were the commensal ciliate Conchophthirus acuminatus and free-living nematodes Chromadorina bioculata and Laimydorus sp. Unidentified chironomid larvae and aquatic mites were also occasionally observed in the mantle cavity. The finding of host-specific ciliate C. acuminatus suggests that zebra mussels invaded Lake Erken at the juvenile or adult stage.