Nitzschioid diatoms are an associated group of long, skinny diatoms with a distinct raphe system.  Its raphe looks like a set of train tracks which crosses the cell on both valves from tip to tip, staying closer to the valve margin on one side.  The raphe is usually on opposite sides on the front and back valves.  Typically, the raphe is positioned along or near the valve margin; raphe on the valve face is called "eccentric."  Because of their well-developed raphe system these diatoms are highly motile, and are common in the sediments of almost any freshwater body. 

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Because there are so many species of Nitzschioid diatoms which look very similar, they are notoriously difficult to identify to the species level.  A few species stand out with unique characteristics, but many others are easily confused.  This website highlights the species most commonly found in Lake Mendota, both those which may be identified and those which are without a certain species name.