Genus Chaos Linneaus, 1767
Diagnosis: locomotive amoebae usually polypodial, like a dead tree with thick truncate branches; in rapid locomotion monopodial, large, commonly between 600 and 1500 µm long, but up to 5000 µm; pseudopodia usually with ridges; uroid morulate; multinucleate, with up to 1000 or more nuclei; nuclei spherical, biconvex or ellipsoidal discs, with granular nucleolar material; cytoplasm with crystals, often bipyramidal.
Ecology: fresh water, ponds and rivers, especially in floating debris in early spring. Not rare.
Remarks: the only lightmicroscopical difference between Amoeba and Chaos is the number of nuclei. Lightmicroscopically the cytoplasm of Amoeba proteus looks identical with that of Chaos carolinense (Andresen, 1956). I have collected populations of Chaos with both multinucleate and uninucleate specimens!
I have sampled and observed a large number of Chaos-specimens in the Netherlands (several wide spread locations), Sweden (Mörrum-river) and England (Cambridge, pond). All these amoebae had, even within a population, spherical, discoid or convex shaped nuclei, varying in size from 9.6-48.0 µm.
Most measurements in literature come from cultures. Chaos carolinense has been cultured for decennia all over the world. The culture of Chaos illinoisense became extinct after 18 years, but this species was recently rediscovered in North-West Russia. In fact we don't know much of these large amoebae, though they aren't very rare, but who is looking for them?
Though a key to the species seems to be a handy instrument for the beginner, for an experienced worker it is a source of doubt, a minefield. Look at the description of the species below.
Key to the species:
|1||Polypodial forms 700-2000 µm; monopodial forms up to 5 mm or rarely more; nuclei biconvex discs, 22-31 µm (mean 27 µm); up to 1,000 nuclei per amoeba; most crystals bipyramidal; cyst reported.
|2||Polypodial forms 500-800 µm; monopodial forms up to 1500 µm; nuclei spherical, 14-16 µm; several hundred nuclei per amoeba; numerous large bipyramidal and plate-like crystals; cysts smooth, spherical, ovoid or elliptical, with endocyst and ectocyst widely separated; cyst diameter 250-350 µm.
|3||Polypodial forms 240-820 µm; monopodial forms up to 1200 µm; nuclei ovoid or biconvex discs, 13-23 µm; 6-60 or more nuclei per amoeba ; crystals bipyramidal; no cysts observed.
|4||Polypodial forms about 500 µm; monopodial forms 420-980 µm (mean 816 µm); amoebae usually monopodial in locomotion, with distinct lateral wrinkles, few amoebae are polypodial; crystals truncate bipiramids, spindles and cubes; nuclei discoid, biconvex, about 20 µm in diameter and 6-30 per amoeba; floating form of radial type.
|5||Polypodial forms 360-600 µm; monopodial forms up to 1300 µm; nuclei spherical, discoid, concave or convex shaped, 9.6-48.0 µm (mean 22 µm; 2-119 nuclei (mean 27 µm) per amoeba; crystals bipyramidal and plate-like, 2.2 µm, sometimes up to 7.9 µm; cysts observed.
|6||Polypodial forms 280-500 µm; nuclei spherical or convex shaped, 11.2-41.7 µm; 1-48 nuclei per amoeba; crystals bipyramidal; no cysts observed.