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Name derivation:

Greek kyklos meaning circle.

Classification:

Cyclotella (Kützing) Brébisson, 1838; 111 of 139 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013).

Order Thallasiosirales, Family Stephanodiscaceae

Morphology:

Drum shaped discoid cells are generally circular in valve view, but can also be elliptical. Most species of Cyclotella are free floating single cells, but can be connected with gelatinous threads from valve to valve. They can also be connected by a mucilaginous sheath or envelope that surrounds the cells. In valve view the ornamentation appears to have two spherical regions. The inner region can be smooth or have fine and irregular punctae. The outer circle has punctae (spots or puncture marks) or striations that radiate outwards towards the edge. The girdle view appears rectangular in shape and the overlapping valves may be smooth or wavy with no intercalary banding. The protoplast of the cell contains several round chromatophores.

Similar genera:

Coscinodiscus differs in its ornamentation in valve view. It lacks the two distinct regions of ornamentation.

Stephanodiscus differs in its ornamentation in valve view also. Stephanodiscus has punctae that radiate from the center and form striations that alternate with a smooth space.

Habitat:

Mostly marine, but can be found in brackish and fresh water systems. Most of the fresh water species are planktonic and are widely distributed across the United States .

References:

Brébisson, [L.] A. de  1838.  Considérations sur les diatomées et essai d'une classification des genres et des espèces appartenant à cette famille. pp. 1-22. Falaise: Brée l'Ainé Imprimeur-Libraire.

Guiry, M.D. & Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 19 September 2013.

Hasle, G.R., and E.E. Syvertsen  1997.  Marine Diatoms.  In:  Tomas, C.R. (Ed.) Identifying Marine Phytoplankton. Academic Press.