foraminifers

Foraminifers, commonly called forams, are a group of single-celled eukaryotes in the phylum Foraminifera within Rhizaria. They are best known for their tests, or shells, which are most often made of calcium carbonate, though some species use organic material or agglutinated sediment particles cemented together. The cell extends pseudopodia through openings in the test to capture prey and to move, forming networks that help in feeding and locomotion.

Most foraminifers are marine, occupying a wide range of habitats from the deep ocean floor to shallow coastal zones. They are divided into planktonic forms that drift in the upper water column and benthic forms that live on or within sediments. A minority inhabit freshwater or brackish environments. Sizes range from a few micrometers to several centimeters in rare cases.

The fossil record of foraminifers is extensive, tracing back to the early Cambrian period. Their calcareous tests fossilize readily and accumulate in thick sediment layers, contributing to carbonate deposits such as chalk and limestone. Because they are abundant and diverse in many marine settings, forams are central to biostratigraphy and paleoceanography, aiding in dating rocks and reconstructing past ocean conditions.

In modern research, the chemical composition of foram tests, particularly oxygen and carbon isotopes, provides proxies for past seawater temperature, ice volume, and carbon cycling. Reproduction occurs through sexual and asexual means in different species, and some planktonic forms harbor symbiotic algae that enhance nutrient exchange. Foraminifers remain key indicators of environmental change and contributors to marine sedimentology.