The major organel of an amoeba is the nucleus. Its main function is to direct cell activities, as reproduction, eating and grow, which it does by causing the production of specific enzymes to carry out chemical reactions.  It contains the amoeba’s DNA, the “blueprint” of cell function, which instructs the cell how to make those enzymes.
Each amoeboid cell contains at least one nucleus. Larger cells are often multinucleate.
The morphology of the nucleus, its size and the number can be useful differential characters. According to the classification of Raikov (1982) two principal types of nuclei are found in amoebae:

  1. vesicular nuclei with one, usually central nucleolus, sometimes with a few additional very small nucleoli;
  2. ovular nuclei with several to many small nucleoli (Fig. 1).

Fig. 1. Left: vesicular nuclei of Difflugia biconcava and D. gramen. Right: ovular nuclei of Difflugia amphora and D. distenda.

Below: photomicrographs of some characteristic nuclei:

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