Ameba (eng. Amoeba) is an RPG about single cell organisms designed by Risto J. Hieta and it was part of his Arctic Ranger Productions series of small RPGs in the beginning of 2000's.
Ameba is a very humoristic RPG, since the idea is to play a single cell organism, the rules and adventures have to be simple as well. The rulebook has suggestions for adventures relevant for amoebas. There is also a persistent rumor that this game has also been played as LARP by players in sleeping bags.