Cyclostephanos dubius (Hust.) Round in Theriot et al., Brit. Phycol. J. 22 (4): 346. 1987.

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

Cyclostephanos dubius (Hust.) Round in Theriot et al., Brit. Phycol. J. 22 (4): 346. 1987.

Basionym.

Stephanodiscus dubius Hust., Krypt.-Fl. Deutschl., 2.Aufl., 7 (1): 367, fig. 192. 1928.

Synonyms.

Cyclotella dubia Fricke in A.W.F. Schmidt

Morphological description.

The frustule is disciform, valve face concentrically undulate, 13.6-21 μm in diameter, striae multiseriate with 9-12 areolae in 10 μm, ribs continue on the curve of a valve, spines grow from each rib (Fig. 7G ).

Ecology.

Cyclostephanos dubius is considered to be a pelagic taxon, planktonic component of both fresh and brackish lakes ( Cholnoky 1968). Often indicating meso- to eutrophic conditions, sometimes recorded for hypertrophic lakes ( Van Dam et al. 1994; Kirilova et al. 2010). The species is common in flowing and stagnant water in coastal area, oligosaprobic, alkalibiontic, halophilous "0.0-5 g/dm3" ( Hustedt 1957); pH value above 7.0 ( van der Werff and Huls 1957-1974; Foged 1973).

Distribution.

This species was found above Mykolaiv city in the Southern Bug River bed (Table 1 ). From Ukrainian territory, it is known from the Dnipro River, the Dnipro-Bug Estuary ( Topachevsky and Oksiyuk 1960; Vladimirova 1971) and the Danube River ( Tsarenko et al. 2009).

Cyclostephanos dubius is a cosmopolitan species, recorded for Berlin, Germany ( Geissler and Kies 2003) and further sites in Europe (Hungary, Dania, Estonia, Moldova, Russia, Ukraine), Asia (Georgia, Russia, Uzbekistan), North America (Canada, USA), Africa (Egypt); Baltic and White Seas ( Tsarenko et al. 2009; Kiss et al. 2012; Genkal et al. 2020).

Figures

Figure 7. SEM (A-E, G, H) and LM images (F) of species found in the transitional zone at Mykolaiv city, valve views: A Cyclotella cryptica B Cyclotella marina C, D Cyclotella meduanae E, F Cyclotella meneghiniana G Cyclostephanos dubius H Cyclostephanos invisitatus, with arrows shown on A, D, H marginal and central fultoportulae, B marginal fultoportulae, F central fultoportulae. Scale bars: 2 μm (B, D); 4 μm (A); 5 μm (C, E); 10 μm (F-H).