I find Spirostomum teres mainly in habitats where a thick layer of fallen leaves is present on the bottom. The specimens occur most frequently in this decomposing mass of leaves. Compared to Spirostomum minus and Spirostomum ambiguum, however, Spirostomum teres is considerably rarer in my habitats.

Spirostomum teres possesses an ellipsoidal macronucleus (s. fig. 6) and can therefore be easily distinguished from the similar species Spirostomum minus, which possesses a moniliform macronucleus. In addition, Spirostomum teres is usually slightly yellowish in color. The considerably larger species Spirostomum ambiguum is distinctly brown in color and also possesses a moniliform macronucleus.

In the pellicle of Spirostomum teres, there are bands of granules (s. fig. 2). Within these bands, the granules partly form orderly rows, which alternate with disorganized areas. However, a rough arrangement of the granules in 3–4 rows can be recognized (s. fig. 3).

The mitochondria are arranged directly beneath the bands containing granules. They can easily be recognized as short, sausage-shaped structures with a length of 1.5–3.5 µm (s. fig. 4). They provide the energy for the cilia, which are arranged in rows between the bands of granules.