One-celled creatures are microscopic organisms that consist of only one cell. Amebas (6 letters) and amoebas (7 letters) are two examples of one-celled creatures. Amebas and amoebas are both protozoa, which are single-celled organisms that lack a cell wall and have the ability to move and change shape. They feed by engulfing food particles with their pseudopodia, or temporary extensions of their cell membrane.