Shelled amoebae. Coloured scanning electron micrograph (SEM) of shelled (testate) amoebae, single-celled (protozoan) organisms found in damp soil, leaf litter and pools. There are two main types of shelled amoeba; these shown forms their tests (shell) by producing small plates, cemented together. Other types use sand grains or other particles to form a test. Magnification: X 950 when printed at 10 centimetres wide.