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).