Cyclotella (Kützing) Brébisson
	From Greek kyklos, "circle"
	Cyclotella is a small, centric diatom with cells only 3-5 µm in diameter. The valves are short and drum-shaped. The circular valve face has rows of areolae radiating from a distinct central area that is sometimes covered by warts, spines, or granules. The cells sometimes have long chitinous bristles that likely help to increase buoyancy or protect the cells from being consumed by herbivores. Each cell has numerous discoid plastids. There are about 100 species. Cyclotella meneghiniana is perhaps the most common species, and has been widely used in growth experiments.   Some researchers believe that the genus should in fact be subdivided, and have created new subgenera or species complexes. Additional phylogenetic research may help to clarify the evolutionary relationships within the genus Cyclotella, as well as its relationships to other groups. So far, most researchers agree on only one new genus, Stephanocyclus, which includes some species that were formerly part of Cyclotella.   Like several other centric diatoms, Cyclotella is able to continue to grow in periods of sustained darkness by making use of glucose or other dissolved organic compounds from the environment.
Some species are known to secrete an organic substance that allows the cells to bind together at the valve face to form linear colonies. Occasionally, the cells may form irregular mucilaginous clusters.     Images of "cleaned" diatom valves with most of the organic matter digested away. The cells are viewed at high magnification with scanning electron microscopy. Note the patterns of pores on the valve face.