Actinocyclus
Ehrenberg 1837 Category: Centric
TYPE SPECIES: Actinocyclus octonarius Ehrenberg
Image Credit: Marina Potapova, Sarah Spaulding
CLASS: Coscinodiscophyceae
ORDER: Coscinodiscales
FAMILY: Hemidiscaeae
- Pseudonodulus present (may be visible only with SEM)
- Several rimoportulae present at margin of valve face
Frustules of Actinocyclus are centric in outline with a relatively narrow mantle. The valve face may be flat or may have concentric undulations in the valve surfaces. Internal openings of rimoportulae are often visible in LM. The genus is distinguished by the presence of a pseudonodulus, a structure found in the three genera Actinocyclus, Hemidiscus and Roperia. The pseudonodulus may only be visible through use of SEM. The areolae on the valve face may give the appearance of being organized into sectors.
Several freshwater species from the western U.S. are extinct and found only in lacustrine sediments. In extant populations, most species are found in marine habitats, primarily in estuaries. Brackish inland waters influenced by anthropogenic nutrients and salts often contain A. normanii, a species considered to be invasive. This species is found in the nutrient-rich habitats as plankton or in the sediment-water interface.
Cite This Page:
Spaulding, S., and Edlund, M. (2009). Actinocyclus. In Diatoms of the United States. Retrieved June 18, 2013, from http://westerndiatoms.colorado.edu/taxa/genus/Actinocyclus
Contributor: Sarah Spaulding | Mark Edlund - January 2009
Reviewer: Sam Rushforth
Citations
Bradbury, J.P. (1984). Fossil Actinocyclus species from freshwater Miocene deposits in China and the United States. Proc. 7th Int. Diatom Sym., Koenigstein, Germany, Koeltz. pp. 667-686.
Bradbury, J.P. and Krebs, W.N. (1995). The diatom genus Actinocylus in the western United States. USGS Professional Paper 1543 A-B.
Hasle, G.R. (1977). Morphology and taxonomy of Actinocyclus normanii f. subsalsa (Bacillariophyceae). Phycologia 16: 321-328.
Holmes, R.M, Peterson, B.J., Deegan, L.A., Hughes, J.E. and Fry, B. (2000). Nitrogen biogeochemistry in the oligohaline zone of a New England estuary. Ecology 81: 416-432.
Kociolek, J.P. and Spaulding, S.A. (2002). Morphological variation, species concepts and classification of an unusual fossil centric diatom (Bacillariophyta) from western North America. Journal of Phycology 38: 821-833.