(Gregory ex Greville) Hustedt 1957 Category: Centric
BASIONYM: Coscinodiscus normanii Gregory ex Greville 1859
REPORTED AS: Coscinodiscus subsalsa (Stoermer and Yang 1969, pg. 33) | Coscinodiscus subtilis var. radiatus (Hohn 1952, p. 271, fig. 2) | Actinocyclus normanii f. subsalsa (Hustedt 1957)
Contributor: Margaret Christie - June 2014
Diameter: 14-72 µm
Rows of areolae in 10 µm:
Valves are disc-shaped, flat to weakly concentrically undulate, with short mantles. Areolae are coarse and polygonal in shape, numbering 8-12 in 10 µm. Areolae often appear to radiate in pseudosectored, or fasciculate groups, of striae from the valve center. Several rimoportulae are located along the valve margin and are generally visible in LM. Rimoportulae are evenly spaced and number 4 - 8 per valve. A pseudonodule is located at the valve / mantle interface, but is often not visible due to its position.
In SEM images, the hexagonal to polygonal areolae and are occluded by flat external cribra. Externally, the opening of the rimoportula and of the pseudonodule are evident. Internally, the rimoportulae have long stalks, external openings are simple.
Some workers recognize the smaller form, A. normanii f. subsalsa (Juhl.-Dannf.) Hustedt from freshwater habitats (Hustedt 1957, Hasle 1977, Stoermer 1993). This form is recognized as differing from the nominate form in size and autecology (Hasle, 1977), with A. normanii f. subsalsa being 16-44 µm in diameter versus 30-110 µm for the nominate form, and the forma subsalsa occurring in fresh, inland waters (Hustedt 1927-1966, Hasle 1977, Stoermer et al. 1993). Although Hasle (1977) was not able to identify morphological discontinuities between the two forms, she and others (Belcher and Swale 1977) recognize that differentiating the two forms (or at least documenting the size distribution within collections) could provide ecological information.
Basionym: Coscinodiscus normanii
Author: Gregory ex Greville 1859
Diameter: 40.6-91.4 µm
Rows of areolae in 10 µm:
Belcher, J.H. and Swale, E.M.F. (1979). English freshwater records of Actinocyclus normanii (Greg.) Hustedt (Bacillariophyceae). British Phycological Journal 14(3): 225-229.
Hasle, G.R. (1977). Morphology and taxonomy of Actinocyclus normanii f. subsalsa (Bacillariophyceae). Phycologia 16: 321-328.
Hustedt, F. (1930). Die Kieselalgen Deutschlands, Osterreichs und der Schweiz mit Berucksichtigung der ubrigen Lander Europas sowie der angrenzenden Meersgebiete. In: Dr. L. Rabenhorst's Kryptogamen-Flora von Deutschland, Osterreich und der Schweiz. Leipzig, Akademische Verlagsgesellschaft Geest und Portig K.-G. Vol. 7, Part 3, pp. 557-816.
Hustedt, F. (1957). Die Diatomeenflora des Flußsystems der Weser im Gebiet der Hansestadt Bremen. Abhandlungen des Naturwissenschaftlichen Verein zu Bremen 34(3):181-440.
Hustedt, F. (1959). Die Kieselalgen Deutschlands, Osterreichs und der Schweiz, 2. Teil. In: Kryptogamen-Flora von Deutschlands, Osterreichs und der Schweiz, (Dr. L. Rabenhorst, ed.), Band VII(2). Reprint 1977, Otto Koeltz Science Publishers, Koenigstein, 845 pp.
Kiss, K.T., Klee, R., Ector, L. and Ács, É. (2012). Centric diatoms of large rivers and tributaries in Hungary: morphology and biogeographic distribution. Acta Botanica Croatica 71: 311-363.
Smol, J.P. and Stoermer, E.F. (2010). The Diatoms: Applications for the Environmental and Earth Sciences, Second Edition. Cambridge University Press, 667 p.
Spaulding, S.A., Kilroy, C. and Edlund, M. (2010). Diatoms as invasive species. In: Smol, J. & E.F. Stoermer (eds). The Diatoms: Applications for the Environmental and Earth Sciences. Cambridge University Press, Cambridge. pgs. 560-569.
Stoermer, E. F. and Yang, J. J. (1969). Plankton diatom assemblages in Lake Michigan. Univ. Michigan, Great Lakes Res. Div. Spec. Rep. No. 47, 168 pp.
Witkowski, A., Lange-Bertalot, H. and Metzeltin, D. (2000). Diatom Flora of Marine Coasts I. Iconographia Diatomologica 7: 1-925.
Actinocyclus normanii was found throughout a sediment core from a marsh near the Christina River, Delaware. The Christina River is part of a a tidal tributary to the Delaware River and includes freshwater and marine diatom species. According to Witkowski et al. (2000), A. normanii is widespread and common in coastal, brackish, planktonic habitats.
This taxon is also documented from waters of Saginaw Bay, Michigan. According to Kiss et al. (1990), this species reflects anthropogenic nutrient enrichment and increases in conductance. Additionally, A. normanii may be considered an invasive species in many sites subject to nutrient enrichment (Kiss et al. 1990). In the Great Lakes, the appearance of A. normanii f. subsalsa along with Stephanodiscus binderanus occurs with human alteration of water bodies (Spaulding et al. 2010).
The variety A. normanii f. subsalsa is reported to differ from the nominate form in in size and autecology (Hasle 1977), but the distinction may not be a real as the nominate variety becomes smaller than published values for the size range (Edlund, personal communication, 2014).