Shelled protozoan. Light micrograph of a shelled protozoan, Nonionina depressula, belonging to the order Foraminifera. The living cytoplasm of the organism can be extruded in the form of pseudopodia (false feet) through pores in the spiral shell. The feet are used both for movement and the capture of food. Foraminifera protozoa are mostly marine; some are sea bottom dwellers while others form part of the surface plankton. The shell of N. depressula is made of calcium carbonate. The shells of Foraminifera creatures which lived in previous geological ages have been compressed and are now major constituents of chalk and limestone rocks. Magnification unknown.