Foraminiferan. Coloured scanning electron micrograph (SEM) of a foraminiferan microfossil from maldives beach sand. Microfossils' are roughly 0.05 to 2mm in size. These are the remains of complete organisms, the common ones are foraminifera and ostracods. Foraminifera are marine single-celled marine protozoa that construct and inhabit a calcium carbonate shell composed of several chambers. These are usually penetrated by pores through which the cellular content is extruded to catch their prey. Magnification: x 130 when printed at 10 centimetres wide.