foraminiferan

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foraminiferan

(fərăm'ənĭf`ərən), common name for members of the class Foraminifera, large, shelled ameboid protozoansprotozoan
, informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies and that show no differentiation into tissues.
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 belonging to the phylum Sarcodina. Most foraminiferan shells are calcareous, but some are siliceous, and others are built of sand grains. Initially, the shell contains a single chamber, and new chambers are added in a characteristic linear, spiral, or concentric series as the organism grows. Some shells reach several inches in diameter, but most species are less than a millimeter in diameter. Long, branching extensions of the cell (pseudopodia) reach from openings in the shell and fuse together to form a net in which plankton organisms are trapped. The net may cover an area 10 times the diameter of the shell, and crustaceans of 1 in. (2.5 cm) or more long may be caught by these much smaller protozoans.

A few foraminiferans live in freshwater or brackish water, but the majority are marine. They are found in all seas at all depths and are extremely abundant. Foraminiferans may be red, brown, or white in color. About 30 pelagic species live in the open sea, the most important belonging to the genus Globigerina.

Foraminiferans live near the water surface when young, but gravitate downward with age. When the animals die, the shells drop to the bottom, forming "globigerina ooze." Such ooze constitutes about half the sediments found on the roughly 50 million sq mi (130 million sq km) of ocean bottom that is covered with sediment in warm and tropical seas. Similar deposits in the past have contributed heavily to the formation of sedimentary rock, and the study of fossil foraminiferans has been extremely important in recognizing geological strata and for dating deposits. Layers of limestone or chalk, such as are found in Dover, England, and in Alabama and Mississippi, solidified from similar deposits of ooze in ancient seas. Foraminiferan fossils have been particularly useful in locating domes where petroleum deposits occur. Limestone used in some Egyptian pyramids contains skeletons of foraminiferans, especially of nummulites, which have coin-shaped skeletons.

Foraminiferans are classified in the phylum SarcodinaSarcodina,
the largest phylum (11,500 living species and 33,000 fossil species) of protozoans). It comprises the amebas and related organisms; which are all solitary cells that move and capture food by means of pseudopods, flowing temporary extensions of the cell.
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, class Granuloreticulosa.

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References in periodicals archive ?
The carbonate sedimentation possibly occurred on middle to inner ramp environment of carbonate platform as suggested by the presence of crinoids, benthic foraminifers, and brachiopods (Okimura, 1988).
Molecular evidence of cryptic speciation in planktonic foraminifers and their relation to oceanic provinces.
Hemleben, "Population dynamics of the planktic foraminifer Globigerina hulloides from the Eastern North Atlantic," Deep-Sea Research Part I: Oceanographic Research Papers, vol.
Due to the relative proximity of the sampling sites to the shore, foraminifers were found to be scarce and the required number of 300 specimens per sample could not be obtained for most samples.
Gametogenesis and the life cycle of the foraminifer Ammonia beccarii (Linne') forma tepida (Cushman).
Non-lethal effects of ocean acidification on the symbiont-bearing benthic foraminifer Amphistegina gibbosa.
In the Oligocene, euphotic conditions prevailed and carbonate production related to these foraminifers (especially Nummulites) declined [49].
* Limestones (packstone) with foraminifers, bryozoans, red algae, gastropods, bivalves, and echinoderms.
Les genres Operculina et Heterostegina (Foraminiferes) et leur utilite stratigraphique.
Anderson of the University of Colorado in Boulder and his colleagues looked to a seeming unrelated subject: the microscopic, hard-shelled foraminifer Globigerina bulloides in sediments of the Arabian Sea.