Foraminifer

Foraminifer, or foraminiferan, is a single-celled protist in the phylum Foraminifera. They are characterized by their tests, or shells, which are typically chambered and perforated, and by pseudopodia that extend through the shell pores for feeding and locomotion. The tests can be calcareous, made of calcite or aragonite, or constructed from sediment particles bound together in an agglutinated matrix. Shell shapes vary widely, including planispiral, trochospiral, and more complex forms.

Most species are marine, ranging from shallow coastal waters to the deep ocean, with a few occurring in brackish or freshwater environments. Reproduction occurs both sexually and asexually, and some species exhibit life cycles with alternating generations and changes in test morphology as they grow.

Ecology and life modes vary: many foraminifers are planktonic, while others are benthic, living on or in sediments. Some larger benthic foraminifers host symbiotic algae (such as dinoflagellates or diatoms), which can supplement nutrition in nutrient-poor tropical waters.

Fossil record and significance: Foraminifera first appear in the late Precambrian or early Cambrian and have an extensive fossil record to the present. Their tests fossilize readily, making them invaluable for biostratigraphy and paleoceanography. Analyses of stable isotopes and trace elements in calcareous tests provide information about past seawater temperatures and chemistry. Today, foraminifers comprise a diverse and widespread group, with thousands of living species and a long, important role in marine ecosystems and geological studies.