Cyclotella horstii Genkal et Kulikovskiy, 2012

Genkal, Sergei & Kulikovskiy, Maxim, 2012, Cyclotella horstii sp. nov. (Bacillariophyta) from Ivankovskoe reservoir (Volga reservoirs, Russia), Phytotaxa 59 (1), pp. 55-63 : 56-60

Cyclotella horstii Genkal et Kulikovskiy sp. nov. ( Figs 2–34 )

Cyclotella planetophora (Fricke) Genkal (1997: 40 , Tab. I, figs 1–6; Tab. II, figs 1–6), exclud. figs & descript.

Frustules shallow, cylindrical. Auxospores 51–60 µm in diameter, 14 striae in 10 µm.Valve face round, 15.7–47.1 µm in diameter, with 2–6 fultoportulae, each bearing 2 satellite pores in central zone, occurring on every third costa. Valve face slightly radial, undulate to nearly flat. Marginal area with 11–16 striae in 10 µm. Striae of unequal length, alveoli, simple oval; valve face central area of variable structure, with 3–7 larger or finer depressions near marginal zone. Rimoportulae (1–3) at marginal zone, one on valves with diameter ≤ 30 µm, 2–3 on valves with diameter ≥ 30 µm. Rimoportulae internal opening orientation from radial to perpendicular, with respect to alveolus.

Type:— RUSSIA. Ivankovskoe Reservoir (Volga Reservoirs Series), Russia, September, 1972, leg. S. Genkal, slide no. C10 (holotypus illustrated in Fig. 13 , in collection S. Genkal, I.D. Papanin Institute for the Biology of Inland Waters of the Russian Academy of Sciences ( IBIW RAS))

Distribution: —From type locality only.

Etymology: —Named after and dedicated to our colleague and friend Professor Horst Lange-Bertalot. Observations:— Cyclotella horstii can be usefully compared to С. kuetzingiana Thwaites (1848: 169) , C. kuetzingiana var. planetophora and C. ocellata .

Comparison with С. kuetzingiana reveals some similarities but С. kuetzingiana has valve depressions in short radial rows and often has papillae and marginal fultoportulae situated on recessed costae. The known diameter of initial valves is 25–27 µm (Houk et al. 2010: Tab. 189, fig. 6; Tab.190, fig. 6).

Relevant data for the valve diameter of C. kuetzingiana var. planetophora is absent from many published accounts (e.g. Cleve-Euler 1951, Hustedt in Huber-Pestalozzi 1942, Kozirenko et al. 1992) but for the original illustrations, Fricke presented images of valves with diameter ranges of 13.3–16.6 µm (in A. Schmidt 1900: Taf. 222, figs 9–12), while other accounts, derived from specimens in the Hustedt collection (BRM), illustrate valves with diameters ranges 6–16.6 µm ( Krammer & Lange-Bertalot 1991, Taf. 51, figs 2–4, Houk et al. 2010, Tab.198, figs 1–13). Hustedt illustrated an account of C. kuetzingiana var. planetophora with images of valves c. 20 µm in diameter (Hustedt in Huber-Pestalozzi 1942: Abb. 491). In contrast, the diameter of the vegetative valves of Cyclotella horstii has a range of 18—47 µm.

The valve diameter of C. ocellata is 3–27 µm ( Zabelina 1951, Genkal & Kuzmin 1979, Klee & Steinberg 1987, Krammer & Lange-Betalot 1991, Schmidt 1993, Kiss et al. 1996, 1999, Hegewald & Hindakova 1997, Acs & Padisak 2001, Håkansson 2002, Houk et al. 2010); only a population found in Lake Khubsugul, Mongolia, was recorded with valve diameters of 43–44 µm ( Edlund et al. 2003; Genkal & Popovskaya 2008). Both С. kuetzingiana and C. ocellata have marginal fultoportulae on recessed costae and papillia outside; C. ocellata has 3 (rarely 4 to 7) depressions ( Wunsam et al. 1995, Kiss et al. 1996, 1999, Genkal & Popovskaya 2008, Houk et al. 2010). Many (4–7) of the large depressions in Cyclotella horstii are situated along the periphery of the central part of the valve, sometimes with small depressions irregularly situated on the valve face. A few rows of granules are found along the marginal edge. Initial valve diameter of C. ocellata has a size range of 10–28.8 µm ( Genkal & Zagorenko 1987, Schmidt 1993, Kiss et al. 1996, Hegewald & Hindakova 1997, Rojo et al. 1999), only in Lake Khubsugul were initial valves found measuring 43–48.5 µm in diameter ( Edlund et al. 2003, Genkal & Popovskaya 2008). Initial valves of Cyclotella horstii are 51–60 µm diameter, 14 striae in 10 µm, and central fultoportulae are absent. Moreover, the maximal size of the lacunas in Cyclotella horstii is between 1–2.2 µm; in C. ocellata it is 0.7–1.0 µm ( Klee & Steinberg 1987, Wunsam et al. 1995, Kiss et al. 1996, 1999, Håkansson 2002, Houk et al. 2010).

Further features of Cyclotella horstii , such as the number of striae in 10 µm, the number of central fultoportulae and satellite pores, the arrangement of marginal fultoportulae with number of satellite pores, the number of rimoportulae and its arrangement in comparison to those in Cyclotella kuetzingiana and C. ocellata have been tabulated ( Table 1).

Figures

FIGURES 2–19: Cyclotella horstii sp. nov. Figs 2–18: Valve view. Fig. 19: External view of initial valve (1–16: LM; 17–19: SEM). Scale bars = 10 µm.

FIGURES 20–25: Cyclotella horstii sp. nov. SEM images, all external views. Scale bars = 10 µm.

FIGURES 26–34: Cyclotella horstii sp. nov. SEM images, all internal views. Figs 26–32: Internal view of valve. Fig. 32: part of internal view of valve, white arrows indicates marginal fultoportulae. Fig. 33: Internal view of initial valve. Fig. 34: Internal view of part of initial valve, white arrow indicates marginal furtoportulae, black arrow indicates rimoportula. Scale bars = 10 µm (Figs 26–31, 33, 34), = 1 µm (Fig. 32).