We have obtained a sequence of the 18S rRNA gene of the species Polychaos annulatum (Penard 1902) Smirnov et Goodkov 1998 using the isolation of a single nucleus from an amoeba cell. Attempts to amplify the 18S rRNA gene from the DNA of this species by conventional PCR were not successful, so we applied the whole genome amplification of the nuclear DNA followed by NGS‐sequencing. The 18S rRNA gene was found among the resulting contigs. The analysis unexpectedly shows that Polychaos annulatum robustly groups within the family Hartmannellidae, but not Amoebidae. This finding warrants revision of the basic morphological criteria used to classify Euamoebida families and show that “proteus‐type” amoebae may belong to other families rather than Amoebidae. This makes taxonomic assignments of such species more complex and the borders between Euamoebida families more nuanced. It is getting evident that molecular data are necessary to clarify the position of species even in this most “classical” order of naked lobose amoebae.