Polychaos centronucleolus  Kamyshatskaya et al., 2020

Diagnosis: Monopodial or polypodial in locomotion, usually with 2–3 short subcylindrical pseudopodia, and rarely “palmate” in slower movement, always with morulate uroid. Nucleus almost spherical with rounded central nucleolus across with several lacunae. Thin filamentous material in karyoplasm, located parallel to the nuclear envelope. No cysts are known.

Dimensions: Length in locomotion 90−220 µm, breadth 20−150 µm. The length/breadth ratio (L/B) varies from 0.7 in palmate cells and up to 6 in orthotactic cells. Nucleus 12−24 µm in diameter, nucleolus 6−14 µm.

Remarks: In contrast to all other species of the genus Polychaos, P. centronucleolus rarely has a palmate locomotive form and no fasciculate uroid. P. centronucleolus is the only species in the genus possessing a nucleus with a centrally located nucleolus. The filaments of the cell coat (ca. 250 nm in length) are thinner and shorter than the filaments of P. annulatum and rather remind filaments in the species P. fasciculatum and P. dubium but are longer than the latter ones.