Oksana Kamyshatskaya^1,2*, Kseniya Taimarova¹, Yelisei Mesentsev¹, Nikita Kulishkin¹ and Alexey Smirnov¹

¹ Department of Invertebrate Zoology, Faculty of Biology, St. Petersburg State University, 199034 St. Petersburg, Russia
² Laboratory of Cytology of Unicellular Organisms, Institute of Cytology RAS, 194064 St. Petersburg, Russia

| Submitted October 26, 2024 | Accepted December 4, 2024 |

Summary

Two strains of a new species named Saccamoeba lotonii n. sp. were isolated from moist plant debris collected in the vicinity of the Kremyotis Falls, Cyprus. In morphology, this species resembles Saccamoeba stagnicola Page, 1974. However, the slowly moving cells of S. lotonii tend to form short hyaline lobes at the anterior or lateral margin. Another distinctive characteristic is the presence of long, twisted mitochondrial cristae. The most outstanding feature of this species is the remarkable diversity of organization patterns of the nucleolar material. Phylogenetic analysis based on 18S rRNA gene sequences groups this species with other members of the genus Saccamoeba. However, since the sequence of the type strain of S. stagnicola does not exist, molecular comparison is impossible. The phenomenon of nucleolar polymorphism has not been previously reported among the "canonical" amoebae of the family Hartmannellidae. It is known only among the genus Polychaos, recently transferred to this family. Transformations in the arrangement of the nucleolar material affect a significant number of cells in culture and are time-dependent. This feature complicates the identification of individual amoebae cells found in environmental samples. This finding highlights the need for molecular identification of hartmannellid amoebae and the necessity for re-isolation of strains of “classical” amoebae species to obtain molecular data.

Key words:  Hartmannellidae, Amoebozoa, Saccamoeba, ultrastructure, nuclear structure