Foraminiferan. Light micrograph of a Calcarina sp. foraminiferan (white) on a matchstick head. 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 pores in the shell (also called a test). Magnification: x28 when printed at 10 centimetres wide.