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Forams are single-celled organisms that typically live in the ocean and produce a mineralized test (shell). Foram tests are generally composed of secreted calcium carbonate (CaCO3), but less commonly they may be composed of organic material or cemented particles scavenged from the sea floor.
Forams produce tests in a range of shapes and sizes. Some tests are simple, single-chambered forms like the one shown in the photo below, while others are multi-chambered and elaborately structured. Typically they are microscopic in size, and generally range from 0.1 to 1 mm. (approximately the size of a grain of sand or smaller). However, in the geologic past, forams with test diameters greater than 10 cm. (4 in.) were not unusual.
Orbulina universa, a sand-sized single chambered test surrounded by delicate spines. (Photo courtesy Dr. Howard Spero, University of California, Davis)
The test houses and protects the organism. Thin organic filaments called rhizopodia (shown as white radiating threads in the photo above) extend through perforations in the test. Do you remember seeing bumps on the test pictured on the Foram Introduction page? Those are pores through which rhizopodia once extended. These rhizopodia help the foram eat, build its test, and depending on the type of foram, rhizopodia help it to move or to stay attached to the sea floor.
Forams eat a variety of foods including organic material dissolved in sea water, algae, bacteria and the larvae of small animals such as crustaceans or fish. Some foram species even host symbiotic algae, which provide the forams with steady nourishment in waters poor in other food sources. By the way, both species pictured on this page host symbiotic algae. Algae-hosting species are most common in latitudes near the equator where other food sources are often in short supply. In their turn, forams are eaten by fish and other small marine animals, and thus form an important part of the marine food web.
Forams are distributed throughout the world's oceans from the North Pole to the South Pole. They are found at all depths and can tolerate the whole range of salinity, temperature, and light conditions. Almost all varieties prefer the marine environment, although a few unusual species are found in fresh water.
There are two major classes of forams,
- benthic - those that live on top of or just within the sea floor, and
- plankontic - those that float freely in shallow, sunlit water. The vast majority of present-day species are benthic.
Globigerinoides sacculfier, a living multi-chambered planktonic foram. (Photo used by permission, Dr. David A. Caron, University of Southern California)
Related Links
Learn more about Protists Forams are members of the Kingdom Protista along with other organisms such as dinoflagellates and diatoms. Check out this site to see gorgeous images and to learn more about Dr. Caron's research.
References
Anderson, O.R. & Lee, J.J. (1991). Cytology and fine structure. In Lee, J.J. and Anderson, O.R. (Eds.), Biology of Foraminifera. (pp. 7-40). London: Academic Press.
Ehrlich, H.L. (1996). Geomicrobiology. New York: Marcel Dekker, Inc.
Haynes, J. R. (1981). Foraminifera. New York: John Wiley and Sons.
Huber, B. T. (1993). What are Foraminifera? Calypso log, 20(3), June 1993. Retrieved August 31, 2004 fromhttp://www.nmnh.si.edu/paleo/foram/foram.html.
Lalli, C. M. & Parsons, T. R. (2001). Biological Oceanography - An Introduction (2nd ed.). Oxford: Butterworth-Heinemann.
Lee, J.J. & Anderson, O.R. (1991). Symbiosis in foraminifera. In Lee, J.J. & Anderson, O.R. (Eds.), Biology of Foraminifera. (pp. 157-220). London: Academic Press.
Murray, J.W. (1991). Ecology and palaeobiology of benthic foraminifera. New York: Longman Scientific and Technical - John Wiley and Sons.
Niles, E. (2002). Life on Earth: An encyclopedia of biodiversity, ecology and evolution. Santa Barbara, CA: ABC-CLIO.
Wetmore, K. L. (1995). Introduction to the Foraminifer. Retrieved August 31, 2004, fromhttp://www.ucmp.berkeley.edu/index.html
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