Foraminiferan shell. Coloured scanning electron micrograph (SEM) of the test (shell) of the British formaminiferan, Elphidium crispum. Foraminifera are single-celled protozoa which construct and inhabit shells composed of several chambers. These are usually penetrated by pores through which the cellular contents is extruded. The organisms live in the sea or salt-water lakes. The shells form an important component of chalk. In previous geological ages foraminifera occurred in such enormous numbers that their shells, largely of calcium carbonate, have formed immense fossil deposits seen today as limestone. Magnification: x100 at 5x7cm size. x242 at 6.75x4.75ins print.