Menoidium obtusum is by far the most common species of the genus Menoidium in the Simmelried. There it sometimes emerges in enormous masses, with thousands of specimens per milliliter. However, until 2017, this species was completely absent from Simmelried. After that, the population grew steadily and reached its current strength around 2019.

Menoidium obtusum can be easily identified by its somewhat clumsy shape in lateral view. The anterior end is not snout-like extended as in Menoidium pellucidum, but obliquely truncated. The distribution of the paramylon grains is typical of Menoidium. The anterior half contains the large paramylon grains, while the posterior half often contains a cluster of small paramylon grains. I also found transparent specimens that lacked large paramylon grains (s. fig. 2 a-b). In these specimens, the nucleus was clearly visible, which is usually obscured by the paramylon grains (s. fig. 2 a). In addition, the delicate, longitudinal striation of the pellicle described by Pringsheim was visible on these transparent specimens (s. fig. 2 a). The specimens in my population were consistently about 50 µm long, with some specimens as long as 58 µm. This is longer than indicated by Pringsheim (30–37 µm). Menoidium obtusum was also described by Alves-da Silva and Friedrich (2009). These authors give a length of 41–42 µm. Due to the few descriptions of Menoidium obtusum, the variability of the body length is obviously not sufficiently evaluated.