Actinocyclus normanii (W. Greg.) Hust. in Abh. Naturwiss. Vereine Bremen 34 (3): 218, pl. 1, figs 5, 6. 1957.

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

Actinocyclus normanii (W. Greg.) Hust. in Abh. Naturwiss. Vereine Bremen 34 (3): 218, pl. 1, figs 5, 6. 1957.

Basionym.

Coscinodiscus normanii W. Greg. in Grev., Quart. J. Microsc. Sci. 7: 80, pl. 6, fig. 3. 1859.

Synonyms.

Coscinodiscus curvatulus Grunow, C. fasciculatus A.W.F. Schmidt, C. normannicus W. Greg., A. normanii f. subsalsus (Juhlin-Dannfelt) Hustedt

Morphological description.

The frustule is drum-shaped, the valve is flat or slightly concave or convex (Fig. 3D-H ). Valve diameter 13.6-26.2 μm, height 3.4-5.2 μm. Areolae are arranged into sectors. The external openings of the process (4-6) are clearly visible on the curved outer surface the mantle (Fig. 3F, H ). The pseudonodulus is located above the openings of the rimoportulae, it has a slight depression.

According to Hasle (1977), there are no significant taxonomic differences between A. normanii f. subsalsus and the nominate form (the ranges of valve diameters coincide), but there may be ecological preferences. Krammer and Lange-Bertalot (2000) did not identify forms, but gave so-called morphotypes that do not have a rank in nomenclature and, according to their data, in the A. normanii population from the Rhine region, a continuous range of forms was observed during the life cycle. Kozyrenko et al. (2008) synonymized A. normanii f. subsalsus with the nominate form and we adhere to their point of view.

Ecology.

Cosmopolitan, planktonic and phytobenthic, alkalibiontic and halophytic species, occurring in brackish inland waters influenced by anthropogenic nutrients and salts, waters with moderate to high conductivity (222-918 μS /cm), pH ranges from 7.8-8.6, at a water temperature between 8.0-25.7 °C and may serve as indicator of nutrient-rich habitats and polluted waters ( Christie 2014; Vidaković et al. 2016).

Distribution.

Actinocyclus normanii is found sporadically in epilithic benthic samples from the the Southern Bug River at the three investigated stations (Table 1 ). It has previously been recorded for Ukrainian water bodies, especially for the Steppe zone noted in the monograph ( Tsarenko et al. 2009) and for the Dnipro-Bug Estuary in particular ( Vladimirova 1971; Zhukinskiy et al. 1989). It may travel upstream with highly mineralized waters from the estuary and appear near Mykolaiv City.

Upstream occurrences have been documented for Actinocyclus normanii f. subsalsus for Germany. According to diatom core analyses, this taxon reached the River Havel around 1900 ( Schönfelder 1997). It was missing in Berlin (which is situated more than 200 km inland from the North and Baltic Seas) in the 1830s-1850s (Jahn and Kusber, unpubl. data from the Ehrenberg collection at BHUPM) but occurred in recent samples at the beginning of the 20th century ( Kolbe 1925; Geissler and Kies 2003) where it became an established part of the flora ( Geissler and Kies 2003; Geissler et al. 2006). It was discussed by Schönfelder (1997) that a prerequisite for naturalisation might be the anthropogenically induced increase of salinity over the minimum value of salt tolerance. In other inland waters, e.g in the Czech Republic, the taxon occurred but did not establish ( Fránková-Kozáková et al. 2007).

Additionally, it is a widely distributed species occurring in Europe, North and South America, the islands of the Atlantic Ocean, Africa, Asia, Australia, and New Zealand ( Guiry and Guiry 2021). However, the species was considered invasive for Russia (see Kaštovský 2010; Korneva 2014) but was not included in the Handbook of alien species in Europe, outcome of the DAISIE (Delivering Alien Invasive Species Inventories for Europe) project ( Handbook of alien species in Europe DAISIE 2009).

Figures

Figure 3. LM (A, B) and SEM (C-H) images of species found in the transitional zone at Mykolaiv city: A Aulacoseira islandica, valve view B Aulacoseira nivalis, valve view C Aulacoseira subarctica, girdle view of complete frustule D-H Actinocyclus normanii valve view (D pseudonodulus shown with arrow, E, G) and girdle view (H, F). Scale bars: 10 μm.