Not only does Amoeba dubia have the largest known genome of any organism, at 670 billion base pairs, which is 200 times larger than the genome of humans, it's also a monster protozoan.  A. dubia can grow to be as large as a millimeter in length, and can be visible to the naked eye.  If you are a single celled organism, that's Godzilla, but even the monster A. dubia isn't the largest member of the amoebozoans.  Multinucleate amoeba of the genus chaos, such as Chaos carolinensis, can grow up to 5 mm in length.