Diagnosis: Test ovoid, usually with a short but distinct aboral protuberance; test circular in cross-section, sometimes compressed, usually composed of small and medium pieces of quartz; protuberance sometimes slightly bent; shell with a short but distinct neck or collar, ornamented with more or less circular evenly spaced mineral particles;between these particles organic cement is visible; pseudostome circular; zoochlorellae in all living cells observed; nucleus spherical, with a central nucleolus.
Dimensions: My measurements: Length 111-151 µm (n > 20); nucleus 36 µm (n=1)
Ecology: In sediment of a ditch in Den Treek, The Netherlands.
Remarks: This species has a characteristic denticulated collar, though this phenomenon is not well developed in all specimens. I found this species only once in the sediment of a shallow ditch. Specimens at this location were mostly alive. Between the typical specimens, with protuberances, also specimens with a smooth fundus were present and once a shell with two protuberances.
This species could be identical with D. difficilis Thomas 1954. However, it is larger then described by Thomas and similar specimens which I collected from the Naardermeer (2015, 2019). These dimensions are:
Thomas: 83-93 µm
Naardermeer: 80-117 µm
Den Treek: 111-151 µm.
The shape and morphological structure of the nucleus from the population of Den Treek is very similar to the ones from the Naardermeer.