Cyclostephanos dubius (Fricke) Round in Theriot et al. 1987 Category: Centric
BASIONYM: Cyclotella dubia Fricke in Schmidt et al. 1900
SYNONYM(S): Stephanodiscus dubius (Fricke) Hustedt 1930
Contributor: Lena Ivarsson - June 2011
Length Range: 8.6-18.5 µm
Striae in 10 µm:
Valves are centric, with distinct costae. The valves are strongly concentrically undulate and show complementarity, with the central area of the valve face being either concave or convex. Characteristic chambers, called alveolae, are present near the valve margin. In large specimens, the central areolae are often organized into radial striae. In small specimens, the central areolae appear to be scattered randomly. A single rimoportula is located on the mantle, on an extension of a costa. Several central fultoportulae are positioned on the valve face, forming an irregular ring. Fultoportulae are also present on the mantle, on an extension of every second to third costa. Costae number 9-12 in 10 µm.
Based on European (West Germany, Poland, and Sweden) specimens, Håkansson and Hickel (1987) distinguished two morphotypes of Cyclostephanos dubius. Morphotype 1 was distinguished by more heavily silicified specimens, with coarse structure. The diameter of the valves was reported as 4.9-22.5 µm, with 9-12 costae in 10 µm. Morphotype 2 was distinguished as more weakly silicified, with finer structure. Morphotype 2 diameter ranged between 11.2–35.0 µm, with 12-18 costae in 10 µm. A central rosette, or annulus, is present in most morphotype 2 specimens. The morphotypes also differ in the length of the costae. Morphotype 1 has costae 1.25 µm in length, while morphotype 2 has slightly shorter costae, 1.0-1.25 µm in length. This feature, however, is only visible in SEM. The fultoportulae of morphotype 2 are arranged in an irregular ring near the center of the valve face and visible in LM. This feature however is not visible for morphotype 1. The material examined from West Okoboji Lake consisted only of specimens conforming to morphotype 1. Hickel and Håkansson (1987) also describe the occasional presence of spines in both morphotypes, with no spines, to spines on every second to sixth costa, to spines on every costa. No spines were been observed in specimens from North America.
Note that Round’s (1982) description of the genus Cyclostephanos was invalid. Consequently, all of the taxa transferred to Cyclostephanos at that time were also invalid. In Theriot et al. (1987), the genus was validated the name Cyclostephanos dubius was also published.
Basionym: Cyclotella dubia
Author: Fricke in Schmidt et al. 1900
Length Range: µm
Striae in 10 µm:
Krim, rec. S.: C. dubia n. sp. – (Stephanodiscus?)
Anderson, N.J. (1990). The biostratigraphy and taxonomy of small Stephanodiscus and Cyclostephanos species (Bacillariophyceae) in a eutrophic lake, and their ecological implications. British Phycological Journal 25(30: 217-235.
Bradshaw, E.G. and Anderson, N.J. (2003). Environmental factors that control the abundance of Cyclostephanos dubius (Bacillariophyceae) in Danish lakes, from seasonal to century scale. European Journal of Phycology 38(3): 265-276.
Casper, S.J. and Scheffler, W. (1987). Beobachtungen an Cyclostephanos dubius (Fricke) Round (Bacillariophyta, Sceletonemaceae) in Gewässern im Norden der DDR. Limnologica (Berlin) 18:451-456.
Hickel, B. and Håkansson, H. (1987). Dimorphism in Cyclostephanos dubius (Bacillariophyta) and the morphology of initial valves. Diatom Research 2(1): 35-46.
Krammer, K. and Lange-Bertalot, H. (1991). Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (Eds.). Süsswasserflora von Mitteleuropa. 2(3): 1-576. Gustav Fisher Verlag, Stuttgart, Germany.
Round, F.E. (1982). Some forms of Stephanodiscus species. Archiv für Protistenkunde 125(1-4): 357-371.
Schmidt, A. (-). (1874-1959). Atlas der Diatomaceen-Kunde, von Adolf Schmidt, continued by Martin Schmidt, Friedrich Fricke, Heinrich Heiden, Otto Muller, Friedrich Hustedt. Reprint 1984, Koeltz Scientific Books, Konigstein, 480 plates.
Theriot, E.C., Håkansson, H., Kociolek, J.P., Round, F.E. and Stoermer, E.F. (1987). Validation of the centric diatom genus Cyclostephanos. British Phycological Journal 22: 345-347.
Theriot, E. and Stoermer, E F. (1982). Observations of North American populations of Stephanodiscus (Bacillariophyceae) species attributed to Friedrich Hustedt. Transactions of the American Microscopical Society, 101: 368-374.
Cyclostephanos dubius was found in great abundance in a plankton net sample from Beck’s Canal, West Lake Okoboji, Dickinson County, Iowa. Beck’s Canal is a shallow set of channels connecting wetlands and residential areas and has a heavily exploited shoreline. The surrounding area mostly consists of agricultural land. The sample was collected 25 May 2011, water temperature was 19.2°C, conductivity measured 430 µS/cm, dissolved oxygen was 6.4 mg/L and the pH was 7.3.
Several studies of C. dubius have been done in Europe (Hickel and Håkansson 1987, Casper and Scheffler 1987, Anderson 1990, Bradshaw and Anderson 2003), but C. dubius has been less frequently reported from North America (Theriot and Stoermer 1982).
Cyclostephanos dubius is considered to be a halophilic species of both fresh and brackish lakes. In Sweden, C. dubius has been found in high abundance in eutrophic lakes with high conductivity (Hickel and Håkansson, 1987). High abundance of small centric, planktonic diatoms is often used as an eutrophication indicator (Anderson 1990).
Beck’s Canal, West Lake Okoboji, where the sample was collected.
Credit/Source: Lisa E. Allinger
Beck’s Canal, West Lake Okoboji, close to where the sample was collected.
Credit/Source: Lisa E. Allinger