Cyclotella

Taxonomic Information

Generitype: Cyclotella tecta Håkansson & Ross 1984 (= Cyclotella distinguenda Hustedt 1927) (type conserved)

Genus Description:

Valves circular (usually), flat or undulate (tangential or concentric), and with shallow mantle (seen in girdle view). Valve margins without spines but strutted processes sometimes visible. Valve face with outer zone of striae (alveoli) and central area unmarked or irregularly punctate, occasionally alveolate. Rimoportulae often visible in the central area.

Updated Description (Håkansson, 2002)

Cells drum-shaped, solitary, in pairs, or in colonies. Numerous discoid plastids. Valves circular with two differing morphological features on the valve face: a central and a marginal area. The central area is flat to tangentially undulate; in some species a minor part of the marginal area borders the undulation. The central area is smooth, can have aparent striation or wrinkles, or has a colliculate structure. None to several valve face fultoportulae are present, sometimes with a slightly thickened external opening. Internally the short tubulus is surrounded by three satellite pores. Sometimes valve face fultoportulae with one, two, or even four satellite pores can be found scattered in between those with the normally three satellite pores. This is considered as abnormal and should not be used as a morphological differentiation. The marginal area is striated and has striae and interstriae of different width and length. In most cases the interstriae are raised, rows of areolae can, however, be found even on these. At the valve face/mantle junction spinnulae or spines can be present. The striae and most of the interstriae continue onto the mantle. Those interstriae which continue have at their end external opening of the mantle fultoportulae (sometimes slightly thickened). Internally the short tubulus has three or two satellite pores. If they have two satellite pores these are towards the edge of the valve and towards the face/mantle junction, in a radial position. In between the ring of the mantle fultoportulae the external opening of the rimoportulae either round or slit-like is located. The internal labium is either sessile or stalked and differs in its angle to the radius of the valve.