candidate: Examples include : Xenophyophores , protozoans of the phylum Foraminifera , are the largest examples known , with " Syringammina fragilissima " achieving a diameter of up to " Nummulite " , foraminiferans " Valonia ventricosa " , an alga of the class Chlorophyceae , can reach a diameter of " Acetabularia " , algae " Caulerpa " , algae " Gromia sphaerica " , amoeba " Thiomargarita namibiensis " is the largest bacterium , reaching a diameter of up to 0.75 mm " Epulopiscium fishelsoni " , a bacterium