I have only ever found Chaetonotus larus once in samples from the Schwemm Moor in Austria. As the species is very small, it is possible that I have overlooked it in my other localities.

Unfortunately, I have only been able to examine a single specimen more closely. It was 115 µm long, which is pretty much in the middle of the range of 80–150 µm given by Schwank (1990). This small size is also the first important feature for identification. The dorsal scales are three-lobed with a keel and a curved, simple spine (s. fig. 5). Their exact shape is difficult to recognize even in heavily crushed specimens, as they are pressed into the cuticle by the spine when the layer thickness is reduced. 

I was only able to examine the ventral side from the dorsal side. However, the small, keeled scales were still clearly visible (s. fig. 7). The anterior third, approximately at the level of the pharynx, is free of ventral scales or so delicate that they are no longer contrasted (s. fig. 7). This is another important feature of Chaetonotus larus. I could only recognize two terminal scales (s. figs 7 and 8). Schwank does not mention the number of terminal scales, but he draws 4 terminal scales (s. drawings above). This may be due to the fact that the species is apparently quite variable. Schwank mentions that the species Chaetonotus larus probably conceals other similar species such as Chaetonotus aculeatus or Chaetonotus sphagnophilus, which have only slightly different scale shapes.