Polychaos annulatum (Penard, 1902) Smirnov & Goodkov, 1997
Diagnosis: medium-sized amoeba with an irregular polypodial shape during slow locomotion; palmate form with some short parallel pseudopodia; uroid bulbous in monopodial locomotive form and fasciculate in palmate form, sometimes with villi, usually very large fasciculate uroid, up to 1/2 of the body; crystals vary in shape and size, from small and irregular to bipyramidal and relatively large; monopodial form during rapid locomotion, may loose any distinct uroidal structures or to have bulbous uroid; nucleus spherical, with the nucleolar material forming a perforated sphere inside the nucleus, situated at some distance of the nuclear envelope. One contractile vacuole. No cysts reported. Floating form of radial type, with spherical central mass of the cytoplasm and short thick radiating pseudopodia. Often amoebae float without taking the specialized floating form.
Surface coat consists of very fine filaments,about 330 nm in length, often collapsing under inappropriate fixation.
Dimensions: Literature 220-325 µm long, nucleus 12-25 µm; my measurements: monopodium 74-250 µm, nucleus 11-25 µm; crystals up to 5 µm.
Ecology: fresh water, on water plants and in sediments of ditches and shallow peat bogs.
Remarks: a common species. I have collected it from several locations in the Netherlands (Naardermeer, Bert Bospad, Kromme Rade, Laegieskamp, IJsselmeer). This species can be confused with Polychaos dubium, but can easily be distinguished by its characteristic nucleus and its smaller size.
This species is varying in the size. Smaller specimens have less pronounced pseudopodia and look more like a Mayorella. In one of my cultures some specimens had a nucleus with a central nucleolus. I have found it together with Trichamoeba sinuosa.
This species may also be confused with Polychaos fasciculatum, however the latter has very distinct nuclear structure and often very irregular crystals. Careful examination of 3D organization of the nucleolus always excludes any doubts about the species identification. Comparison of Polychaos fasciculatum-like” amoebae was done by Smirnov & Goodkov (1998).