Cylindrotheca Iconic
  1. Frustules narrow and elongate, with drawn-out ends
  2. Frustules twisted
  3. Frustules lightly silicified

Cylindrotheca cells are solitary and are characteristically needle-like, thin and elongated in shape. The ends of the cell tend to be protracted, meaning "drawn out". The frustules are lightly silicified. The valves, including the keel and raphe canal, are twisted. As a result of the strong twist of the raphe system, the cells rotate as they move. The girdle bands are numerous and also, like the valves, are long and narrow. The silica is held together by organic matter and some species have regions of the valve consisting only of organic matter (Reimann et al. 1965).

In freshwater, Cylindrotheca is characteristic of high alkalinity habitats. The occurrence of this diatom is often overlooked because the lightly silicified cells are easily broken and destroyed with standard processing techniques. A motto of Dr. Charlie Reimer was "Think like a diatom", and he preferred to think like Cylindrotheca. He and Cylindrotheca favored the small pools of water that form in depressions made by cow's hooves. Reimer's favored place to find these cowprints was in Excelsior Fen, Dickinson County, Iowa.

Cylindrotheca also has many marine representatives, all typical of benthic mudflats (Apoya-Horton et al. 2006, Reimann and Lewin 1964).