Until recently, it seemed that amoebae of the genus Thecamoeba could be reliably identified using light-microscopic char-acters. However, recent studies show the presence of sibling species in the genus Thecamoeba, which can only be reliably distinguished based on the molecular data. Here we describe a new freshwater species, Thecamoeba vumurta n. sp., which has minor morphological differences in the light-microscopy and the cell ultrastructure with the widely distributed species Thecamoeba striata. Taken alone, these differences are hardly sufficient to justify a new species, but considerable differences in the SSU rRNA gene sequence leave no doubts that this is an independent species, forming a pair of sibling species with T. striata. The SSU gene sequence in both these species is very divergent from other thecamoebids. BLAST search identifies neither of these sequences as belonging to Thecamoeba. This study further supports the conclusion that gene sequencing is necessary for the reliable identification of Thecamoeba species. To clarify the situation with sibling species, we propose distinguishing three morphologically defined species groups within the genus Thecamoeba and using their names (instead of taxonomic species names) in case a similar species is identified without molecular studies.(c) 2022 Elsevier GmbH. All rights reserved.