A tiny amoebozoan with a locomotive size of about 10 μm was isolated from an inland brackish water biotope in the northwest of Russia. During locomotion, amoebae were flattened, with broad anterior hyaloplasm and short ventral subpseudopodia that appeared like small bumps. Electron microscopy shows that amoebae are enclosed in a flexible layer of flat oval scales embedded in a matrix and separated from the plasma membrane surface. These characters are in accordance with the phylogenetic placement of this strain, as reconstructed using the nuclear SSU rRNA, actin, and mitochondrial cytochrome c oxidase subunit 1 (Cox1) gene sequences. Morphology and molecular phylogenies warrant the description of the studied strain as a new species, Armaparvus browni sp. nov. This species shows a broad range of salinity tolerance, being able to reproduce in culture under salinity of 2.5 ‰, but not in 0.3 ‰ or artificial freshwater medium. This may be due to an adaptation to brackish water with oscillating salinity and hence A. browni probably cannot expand into truly freshwater habitats.
