Most of morphologically distinct species, nowadays belonging to the genus Thecamoeba were described at the turn of the 19th and 20th centuries. However, no type material was preserved at that time. It caused numerous problems in further re-isolation and identification of these species. F. Page in 1971 and 1977 isolated and re-described most of the known Thecamoeba species, performed neotypification, and established type cultures. Almost all of them are nowadays lost. Accumulation of molecular data has shown that some “classical” morphological species of Thecamoeba have complex genetic structure and probably represent complexes of sibling species. We have isolated from the terrestrial habitat an amoeba strain, identified as T. similis at the morphological level, which possesses 18s rRNA gene sequence identical to that of Page's strain. We provided up-to-date morphological description and illustrations of T. similis, and novel data on the variability of its nuclear structure. We identified molecular signatures that can be used as barcodes for the identification of Thecamoeba similis-like species. Studied amoebae show a tendency to form aggregates on the agar surface. Our observation suggests that it is not an active process but rather a result of the interaction of water droplets covering amoebae and surface tension effects.