Cyclotella atomus Hust. var. atomus in Arch. Hydrobiol. 15: 143, pl. 9, figs 1-4. 1938.

Bilous, Olena P., Genkal, Sergey I., Zimmermann, Jonas, Kusber, Wolf-Henning & Jahn, Regine, 2021, Centric diatom diversity in the lower part of the Southern Bug river (Ukraine): the transitional zone at Mykolaiv city, PhytoKeys 178, pp. 31-69 : 31

Cyclotella atomus Hust. var. atomus in Arch. Hydrobiol. 15: 143, pl. 9, figs 1-4. 1938.

Morphological description.

Frustule low-cylindrical, central part of the valve is slightly tangentially undulated, 3.6-5.6 μm in diameter, clear boundary between regional and central zones absent, 10-15 striae in 10 μm, and a central process (Fig. 6B, C ).

Ecology.

Euplanktonic species, that may exist in marine, brackish or nearshore areas and freshwaters, indicating eutraphentic, α-mesosaprobous conditions and often associated with polluted, warm nutrient-rich water, however particularly tolerating high total phosphorus loads (Denys 1991; Van Dam et al. 1994; Yang et al. 2005; Lowe 2015), halophilic, alkaliphilic, tolerates higher ion concentrations and frequent osmotic stress as well as high temperature conditions and turbulence ( Krammer and Lange-Bertalot 2000).

Distribution.

Valves were found at all investigated sites of the Southern Bug during this research (Table 1 ). For Ukrainian territory, it has been reported for the Dnipro River ( Maystrova et al. 2007).

In general, Cyclotella atomus is a cosmopolitan species ( Krammer and Lange-Bertalot 2000), widespread in freshwater and marine environments in North America, Europe, and Asia, and has also been recorded from Argentina and South Africa ( Poulíčková 1993; Medioli and Brooks 2003; Tanimura et al. 2004; Yang et al. 2005; Wojtal and Kwandrans 2006; Genkal et al. 2020).

Figures

Figure 6. SEM (A-F, H) and LM images (G) of species found in the transitional zone at Mykolaiv city, valve views: A Stephanodiscus minutulus with arrows shown marginal and central fultoportulae B, C Cyclotella atomus var. atomus with arrows shown marginal and central fultoportulae D-F Cyclotella atomus var. gracilis with arrows shown marginal and central fultoportulae on D picture, only central fultoportula on E and central fultoportula and alveolae on (F) G Cyclotella choctawhatcheeana with arrow shown central fultoportulae H Cyclotella cryptica with arrows shown marginal and central fultoportulae. Scale bars: 3 μm (B, C); 4 μm (D, F); 5 μm (A, E, H); 10 μm (G).