Uroglena volvox is very common in my sampling sites. I mainly find the colonies in plankton samples but also between floating plant masses.

Uroglena volvox can be recognized by the gelatinous stalks in the colony, which are already visible without staining (s. fig. 1). These stalks are not hollow (as in Uroglena articulata) but consist of a homogeneous gelatinous strand (s. fig. 4). The gelatinous stalks all start from a central origin in the middle of the colony (s. fig. 4). It is also important to check the number and shape of the golden-brown chloroplasts per cell. In Uroglena volvox there is only one ribbon-shaped chloroplast, which is spirally arranged in the longitudinal axis of the cell. Depending on the focal plane, this may give the impression that there are two chloroplasts. It is therefore important to focus carefully.

In my population I mostly found colonies below 200 µm in diameter. However, in some colonies the cells were longer than 12–20 µm, as indicated by Huber-Pestalozzi (1941). The cells reached a length of up to 30 µm, due to a tapered and elongated posterior end, with which they were attached to the gelatinous stalk (s. fig. 5). Thus the cells had the shape described for Uroglena upplandica. However, in all the colonies I examined, the branched gelatinous strands were clearly visible, which should not be visible in Uroglena upplandica.