Genus Paralieberkuehnia De Saedeleer 1934
Diagnosis: Shell spherical to slightly ovoid, with distinct tubular neck, composed of an organic material, very fine granulated, without any embedded xenosomes; colorless to yellow-brown till dark-brown. Cytoplasm with an asymmetrical bundle of filopodia (peduncle or “Pseudopodienstiel”) which are granular (extrusomes), thin, usually straight, and are able to branch and anastomose, thus forming a network or reticulum. Nucleus relatively large, globular with a central nucleolus. One or two contractile vacuoles.
Ecology: Freshwater; shallow, iron rich water, between Sphagnum, but also in small streams.
Video: I made this video from material which came from the Geul, a small stream at the border of Belgium and the Netherlands. This cell shows anastomosing filopodia.
Remarks: The designation of genus Paralieberkuehnia is problematic. It was erected by De Saedeleer in 1934 for P. elegantula (Penard, 1904) which he made the type species. Penard describes his species based on the observation of three specimens from two different localities. The shell is as Penard writes “a perfect sphere” with a small tubular neck. De Saedeleer also found three similar specimens, however with an inner tubular structure. He states that Penard may have overlooked that structure.
De Saedeleer writes that Paralieberkuehnia is a free living and locomotive species, while Microgromia-species attach their shell to the substrate. That is what I think makes any sense. But De Saedeleer doesn’t mention this characteristic in his diagnosis! The main difference between Microgromia and Paralieberkuehnia is, according to De Saedeleer, the presence of an inward tubular structure in the latter.
I have seen numerous shells of P. elegans sensu Penard, but only twice shells with an inner tubular structure. I thinks those are different species, because the specimens with an inner tubular structure showed much more a reticulum, which I have never observed in P. elegans sensu Penard.
At this moment, I think that the genus Paralieberkuehnia is characterized by a spherical, non attached shell with straight free moving granulopodia, while Microgromia species have an attached shell with granulopodia appressed to the substrate.
I found this species in Waidring, Austria, Belgium and at several locations in the Netherlands.
An important difference between Paralieberkuehnia at one hand and Microgromia and Apogromia at the other hand is that Paralieberkuehnia specimens are not attached to the substrate, while the other groups are sessile forms. You can often find specimens of Microgromia and Apogromia, and also Microcometes, attached to the cover glass. Their granulopodia are lying on the substrate, while Paralieberkuehnia specimens hang freely and stretch their granulopodia freely in the water around.