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Polychaos dubium
Polychaos dubium, Cardet, France, 2019

Polychaos dubium (Schaeffer, 1917)

Diagnosis: large to medium-sized amoeba with an irregular polypodial shape during slow locomotion; palmate form with some large parallel pseudopodia; pseudopodia tend to fuse at their bases as the main cell mass advances; uroid large, fasciculate, sometimes with villi; crystals relatively large, with many variations, usually squared, bi-pyramidal or rod-shaped, like a candlestick; there are also “paired bodies” and irregular-shaped crystal-like inclusions in the cytoplasm; monopodial form during rapid locomotion; single nucleus, granular, usually discoid, sometimes ovoid or spherical, filled with small nucleolar pieces; floating form when disturbed ovoid or spherical, but soon after becoming star-shaped with several radiating thick pseudopodia of unequal length.
Ultrastructure: Surface coat consists of very fine filaments 170-180 nm in length, radiating from the plasma membrane. Filaments are extremely fine and often collapse under inappropriate fixation. This species has fibrous honeycomb-like inner nuclear lamina, 250-320 nm in thickness. Mitochondrial heteromorphism has been noted

Measurements: Monotactic form 250-750 µm (Schaeffer up to 1000 µm); polytactic form 250-400 µm; nucleus 26-70 µm (mean 36 µm); crystals up to 14 µm; contractile vacuole up to 60 µm.

Ecology: Fresh water, both clean and polluted; sediments of ditches and shallow peat bogs, in streams and canals. Omnivorous. I noticed as food: diatoms, purple bacteria, Mayorella-species, Trinema enchelys and Arcella hemisphaerica, Euglena, Chilomonas, Cosmarium and Trachelomonas species, Peridinium cintum and rotifers.

Remarks: A common species in all seasons, but sometimes abundant in floating debris in early spring, just after the ice on the ditches has melted. I have collected it in the Netherlands, England (Cambridge) and Southern Sweden. This species can be confused with Amoeba proteus, but is distinguished by its remarkable large crystals. These crystals are never abundant, giving the amoeba often a clear appearance.

Polychaos dubium
Polychaos dubium, ditch, Netherlands 2020 – flattened by cover glass
Polychaos dubium
Polychaos dubium, ditch, Netherlands 2020, with nucleus and ingested food
Polychaos dubium
Polychaos dubium, ditch, Netherlands 2020, with typical crystals
Polychaos dubium
Polychaos dubium, Cardet, France, 2019
Polychaos dubium
Polychaos dubium
Polychaos dubium
Polychaos dubium, monotactic shape, cells somewhat compressed by the cover glass
Polychaos dubium
Floating form with extreme slender pseudopodia
Polychaos dubium
Polychaos dubium, 300 µm
Polychaos dubium
Polychaos dubium, three cells, somewhat compressed by the cover glass, c. 256-348 µm long.
Polychaos dubium
Polychaos dubium, monotactic form c. 375 µm long.
Polychaos dubium
Monotactic form
Polychaos dubium
Polychaos dubium
Polychaos dubium, floating form with slender pseudopodia.
Polychaos dubium
P. dubium, crystals in vacuoles.
Polychaos dubium
Polychaos dubium
Different crystals
Polychaos dubium
Polychaos dubium
Crystals and uroid wih villi
Polychaos dubium
Polychaos dubium
Uroid, in cross section and surface structure
Polychaos dubium
Polychaos dubium
Nucleus in Phase Contrast and in DIC
Polychaos dubium
u = uroid; n = nucleus
Polychaos dubium
Polychaos dubium
The same nucleus, c. 45 µm. Notice the small lacuna in the nucleolar material
Polychaos dubium
Polychaos dubium
Nucleus 28 µm and 46 µm Ø
Polychaos dubium
Nucleus 60 µm Ø
Polychaos dubium
Nucleus of Polychaos dubium, 44 µm Ø
Polychaos dubium
Polychaos dubium
Two specimens in a culture dish
Polychaos dubium
A polypodium; B monopodium; C monopodium changing its direction; D variations in crystals (Drawing: Ferry Siemensma)
Polychaos dubium
Polychaos dubium, two cells surrounded by debris.
Polychaos dubium
Four coverings of P. dubium
Polychaos dubium
Uroid of Polychaos dubium
Polychaos dubium
Polychaos dubium, nucleus 36 µm Ø
Polychaos dubium
Polychaos dubium,  palmate form
Polychaos dubium
Polychaos dubium
Polychaos dubium, left: nucleus 39 µm, right: crystals – Weser, Germany
Polychaos dubium
A monopodium with numerous small squared crystals; B-E variations of the uroid; F monopodium with fungi; G palmate shape; H cyst; I spread of the diameter of the nucleus in 36 specimens in one population. (drawing Ferry Siemensma)
Polychaos dubium
A different crystals in three specimen in one culture; B floating form and K after long shaking; C-J different shapes of nuclei; E cup-shaped; G nucleoli, detail of F; I lateral view and J dorsal view. (drawing Ferry Siemensma)
Polychaos dubium
Polychaos dubium, c. 300 µm
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