Is this Acanthamoeba?

[NachoBen]

I have found this beautiful and very active amoeba in a freshwater sample that I took a month ago. It has not begun to abound in the sample until a few days ago. The sample comes from an old disused laundry buddle in the historic city of Trujillo, Cáceres, Spain.



This amoeba seem to match the genus Acanthamoeba, but my specimens are larger. In the bibliography (https://arcella.nl/genus-acanthamoeba/) it is said of Acanthamoeba pyriformis: “Mean cell length is 26.9 μm (standard deviation = 4.2 μm, n = 30) and mean cell breath is 19.3 μm.” But it is clear my amobeae are bigger.

Any idea about real ID? Thank you!

[Sure Squintsalot]

holy cow that's weird.

[NachoBen]

After some research, I think it could be a floating form of Rizhamoeba.

Nonetheless, my specimens don't match some of the features of Rhizamoeba:

a. It does not develop clearly monopodial forms.
b. I have almost never seen them hiding under debris.
c. Last but not least, I have seldom observed the typical flow back of the hyaloplasm down the sides.