Foraminiferan shells. Light micrograph of assorted species of shells belonging to the order Foramini- fera. Single-celled protozoans inhabit these shells which are composed of several chambers and usually penetrated by pores through which the cellular contents (protoplasm) is extruded. The organisms live in the sea or salt-water lakes. Foraminiferan shells form an important component of chalk and of many deep sea oozes. In previous geological ages foraminifera occurred in such enormous numbers that their shells, largely of calcium carbonate, have formed immense fossil deposits. Magnification: x50 at 35mm size.