Foraminiferida

Foraminiferida, commonly known as foraminifers or forams, are a large and diverse group of single-celled marine protists distinguished by their porous shells, or tests. Most foraminifers are heterotrophic and rely on pseudopodial extensions to feed and interact with their environment. They occupy a broad range of habitats, including planktonic forms that float in the water column and benthic forms that live on or within sediments; a lesser number inhabit freshwater systems.

Morphology and biology. The defining feature of foraminifers is their tests, which are usually made of calcium carbonate but can also be composed of agglutinated particles cemented together. Tests are often chambered and arranged in complex patterns, with openings that permit the protrusion of pseudopodia. These reticulopodial networks extend through pores in the test to capture prey, gather detritus, or sense the surroundings. Some species harbor symbiotic algae and rely on photosynthesis to supplement nutrition. Reproduction varies widely among taxa, with most capable of asexual division and many displaying more complex life cycles that include sexual reproduction and optional alternation between different life-history stages.

Ecology and significance. Foraminifers inhabit a wide range of marine environments from shallow coastal seas to deep ocean basins, with planktonic and benthic lineages contributing to marine food webs and sediment formation. Their tests commonly accumulate as part of calcareous sediments and sediments rich in cemented grains. Foraminifers have an extensive fossil record dating back to the early Cambrian and are central to biostratigraphy and paleoceanography. Their stable isotope composition (notably oxygen and carbon isotopes) in tests provides information on past temperatures, ice volumes, and carbon cycling, making them valuable in climate and petroleum research.