How to identify amoebae?

The user should not expect that every amoeba of a described species will have a form fitting into the illustrated one.

Fred C. Page, 1976

Identifying an amoeba may be a big problem. Unless you are a very experienced observer, it is nearly impossible to determine the family or genus of an amoeba based on a single observation. The problem is that amoebae do not have a constant body form, they are polymorphic. A single cell can have different shapes, especially when it is stationary or moves in a non-coordinated manner, often changing the direction of locomotion. Though most amoebae do not have stable morphological characters that could be easily described, there are some light microscopical characteristics which can be used for identification and describing species:

1   general pattern and outline of a moving amoeba;
2   presence and shape of pseudopodia and subpseudopodia;
3   organization of the uroid;
4   shape of an amoeba in cross-section;
5   position of the hyaloplasm in the locomotive cell;
6   cystforming and structure of the cyst;
7   structure of the nucleus.

The locomotive form is possibly the most useful characteristic. Smirnov et al (1999, 2004) distinguish a number of morphotypes, which are useful to determinate families and genera. The system of morphotypes is not a taxonomic classification.
For further information see the excellent guide to the morphology and identification of naked amoebae:

Smirnov, A. V., Brown, S. (2004): Guide to the study and identification of soil amoebae. Protistology 3:148-190.