Polarised light micrograph of Difflugia sp. shelled amoeba. The image shows the entrance to the shell. Difflugia is the oldest and most species-rich genus of testate amoebae, comprising over 300 species. They are found in various freshwater environments like marshes and lakes. Difflugia are characterised by their shell-like structures (tests) which they build from mineral particles. Magnification: 372x when printed 10 centimetres wide.