Foraminiferan shells. Macrophotograph of shells of Calcarina sp. foraminifera. Foraminifera are marine single-celled marine protozoa that construct and inhabit a calcium carbonate shell composed of several chambers. Most live on the sea bottom, feeding using amoeba-like pseudopodia that are extruded through the pores seen here. Magnification: x23 when printed at 10 centimetres across.