Pelomyxa flava
Pelomyxa flava, 300 µm long

Pelomyxa flava Frolov, Chystjakova and Malysheva, 2011

Diagnosis: Mobile pelomyxoids with cylindrically shaped bodies. The cytoplasm is transparent and stained yellow, brown or yellow-green due to inclusions. Hyaloplasm is not expressed. The binuclear stage predominates in the life cycle and plas­motomy occurs at the quadrinuclear stage. Nuclei are of a granular type and the fragmented nucleolar mate­rial is located at the periphery of the nucleus. At all cycle stages, the nuclear envelope is surrounded by microtubules arranged in one row. Flagella are immo­bile. Endosymbionts are represented by large rodlike bacteria with a pronounced longitudinal cleft and two species of smaller rodlike bacteria.

Dimensions: The size of the cells ranges from 100 µm for young individuals to 300 µm for adult locomotive forms. Nuclei 19-23 µm, mean 20.41 µm (Frolov et al, 2011).

Pelomyxa flava
Pelomyxa flava
Nucleus, 19 µm

Ecology: P. flava inhabits swamped stagnant and low-flow fresh water reservoirs at a depth of 20-50 cm and their diet consists mainly of unicellular fungi. In digestive vacuoles, the representatives of chlorophyts and xanthophyts are especially abundant.­
I found this species in large numbers in shallow water in Den Treek and Crailoo. The Dutch specimens were not so bright colored as Frodov et al, 2011 described.

Remarks: In a light microscope, P. flava differs well from the majority of known species by its transparent, bright-yellow and goldish-green cytoplasm and the presence of two nuclei; furthermore, it differs significantly from the binuclear P. binucleata in its organization of nuclei (granular in P. flava and vesicular in P. binucleata), their twofold smaller size (around 20 and 40 µm, respectively), and the absence of a pronounced zone of hyaloplasm.
In the natural P. flava populations, about 95% of cells have two nuclei; the remaining individuals have three or four morphologically similar nuclei. The P. flava nuclei that freely move with flows of the cytoplasm have a granular structure.
Glycogen is only found in cells with two or more nuclei and its granules have a more or less regular ovoid shape in which the longitudinal axis varies is 10-45 µm. The number of glycogen inclusions in the cell is not high and usually amounts to 30-40 per cell.

(All above information from Frolov et al, 2011)
Pelomyxa flava
Locomotive form, 300 µm, with one nucleus visible (arrow).
Pelomyxa flava
Pelomyxa flava, 160 µm, changing direction.
Pelomyxa flava
Pelomyxa flava, 300 µm, with large food remnants.
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