Foraminifera are microscopic unicellular organisms that can be found in all marine environments. Though the creatures are small, foraminifera achieve amazing densities, hundreds of thousands of their shells existing in a single cubic centimeter of sediment.

Foraminifera, also known as forams, may be free-floating, planktonic species, but the vast majority are benthic (bottom-dwellers). The shells, or tests, of the planktonic and most benthic species are composed of calcite, which is the same mineral that comprises bivalve shells. Others construct shells composed of organic material, sediment particles, or mineral secretions. In order that there may be room for additional growth, the tests of most forams are chambered. However, some species exhibit alternate designs, such as open tubes or hollow spheres.

Slender, hair-like reticulopodia extend from the tests of foraminifera and are most often used for locating and ensnaring prey, including bacteria, diatoms, copepods, and single-celled phytoplankton. Yet some of the aquatic organisms have another food source, thriving on the algae that they grow inside their shells. As part of the food chain, however, foraminifera do not only eat, but are eaten, as well. Many species of snails, sand dollars, and small fish graze on the tiny creatures.