The term ONE-CELLED CRITTER can be solved by two crossword solutions, AMEBA (5 letters) and AMOEBA (6 letters). An ameba is a single-celled organism that belongs to the protozoa family. It is typically found in water and feeds on bacteria and other small organisms. An AMOEBA is similar to an ameba but is slightly larger and has a more complex structure. Both amebas and amoebas are able to move around by extending their pseudopods, or false feet.