We isolated and described a brackish-water amoeba, Clydonella sawyeri n. sp. (Amoebozoa, Vannellida), from the littoral habitat in Kandalaksha Bay (The White Sea, northwestern Russia). Morphology of this amoeba corresponds to the initially proposed diagnosis of the genus Clydonella Sawyer, 1975, although it is sufficiently different from other described species of this genus to warrant a distinct species designation. Phylogenetic analysis based on the small-subunit rRNA gene shows that this species is closely related to the two previously studied ATCC strains identified as Clydonella sp., for which only ultrastructural and molecular data were published. Cytochrome oxidase subunit 1 (COI) gene sequence of the studied species was for the first time obtained for Clydonella. Analysis of this marker shows that this genus belongs to Vannellida and is separated from the other vannellids sampled to date. Phylogenetic analysis of the concatenated SSU rRNA and COI genes dataset yields the best resolved position of Clydonella compared to both markers when analysed separately. Based on the data presented we finally link light microscopic, ultrastructural and molecular data in a description of a single strain, which allows a refinement of the diagnosis of the genus Clydonella. (C) 2018 Elsevier GmbH. All rights reserved.