Foraminifers (commonly called "forams") are the largest members of the group of single-celled microbes known as Protists. These tiny creatures are actually the most diverse group of marine organisms known, with more than 60,000 extinct and extant species recognized today. Foraminifera can be found in oceans worldwide, living either on or buried below the sea floor or as free-floating plankton at the water’s surface. The amoeboid cell of a foram contains a hard, internal shell or test that is divided into chambers. The test can either be excreted by the organism, in which case it will be calcitic or aragonitic in nature, or it can be assembled from a mixture of organic glue and sand or other small particles (agglutinated). Traditionally, species have been classified by the morphology of their tests, with groups characterized by test material and internal chamber arrangement. Most species have porous tests (hence foramina, or windows), from which the cell’s cytoplasm can be extruded in long arms called rhizopodia. These pseudopodia aid both in movement and capturing food such as diatoms and detritus. Interestingly, some large, benthic species are known to harbor symbiotic algae in the chambers of their tests, which provide the extra nutrients needed by these foraminifera in order to grow to such a large size.

The genus of the specimen shown here, Calcarina, is known for its large test size and its appealing planispiral arrangement of chambers. In the cutaway movies, these chambers easily standout in green, and in life they would have been home to symbiotic algae and cyanobacteria responsible for providing the foram with the nutrients required for its rapid growth. Calcarina, like other large, benthic foraminifera, prefers warm, shallow water associated with reefs and shelves and is found in high numbers in the Indo-Pacific Ocean where it has been used to evaluate the paleoecology of ancient beach sediments.