Penardia mutabilis Cash, 1904 (fig. 5)

This is a large naked free-living amoeba. Cell shape is variable, spread if adhered to a substrate. The locomotion is relatively rapid. In motion, the amoeba changes its shape, branching in a reticulate net. Pseudopodia can reach 35 μm in length, growing out of a peripheral hyaline fringe of the cytoplasm. Cell length is 300–540 μm, cell width is 80– 110 μm, L/B ratio is 3.5–4. The nuclei are 5–7.5 μm in diameter.

Remarks: the species can be distinguished from closely related species of the genus Biomyxa Leidy, 1875 by cytoplasm’s rapid movement and greenish color (the Biomyxa amoebae have uncolored clear cytoplasm) (Page, Siemensma, 1991).

Distribution: P. mutabilis occurs in Europe (Page, Siemensma, 1991).

Habitats: we found the species in lake Svitiaz (Shatsky National Natural Park, Volyn Region) (Patcyuk, Dovgal, 2012) .

Thus, as a result of the research, 5 amoebae species were found in Ukraine for the first time. According to latest views on the system of naked amoebae (Smirnov et al., 2011; Bass et al., 2009), they belong to 4 genera from 4 classes, 4 orders and 4 families. Four of the species are lobosea naked amoebae ( Rhizamoeba sp., T. quadrilineata, T. verrucosa, Flamella sp.), one is a naked filosea amoeba species ( P. mutabilis). Also, P. mutabilis ecologically belongs to limnic species complex of naked amoebae that is characteristic of Shatsk lakes (Patcyuk, Dovgal, 2012).