Look them up on the internet and they are exactly what is described in the question. They are a freshwater unicellular organism that is green in color and have a red dot on them. Paramecium wouldn't make sense because they don't have a red dot and are not green. Amoeba wouldn't make sense because they don' t have red dots and are kind of just shape altering organisms. Slime mold wouldn't make sense becase they're typically yellow in color with no red dot.
