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Kingdom Protista, Phylum Sarcomastigophora, Subphylum Sarcodina, Superclass Rhizopoda, Class Granuloreticulosea, Order Foraminiferida — Basal Cambrian-Recent

  • Benthic foraminifers: Cambrian-Recent (early forms were exclusively agglutinating)

  • Calcareous benthic foraminifers — Ordovician-Recent; large forms from Late Carboniferous-Recent

  • Planktic foraminifers: Middle Jurassic-Recent

Despite being single-celled protozoans, this is a very complex group of organisms, with 12 suborders recognized by Loeblich and Tappan (1984) and some 60-80,000 species identified from Phanerozoic strata. So many shape, size, and wall-structure varieties exist, however, that this chapter can provide only the minimal information needed to identify the most important groups.

Modern foraminifers are fully marine to marginal marine organisms, extending from the intertidal zone to abyssal oceanic depths and from cold-water polar settings to warm tropical environments. Some genera live in marginalmarine hypersaline or subsaline water bodies where they are commonly found in great numbers (but low species diversity).

Most foraminifers are benthic organisms (of the roughly 4,000 modern species, only about 40 are planktic).

Some of the largest living benthic species harbor symbiotic algae in their tissues and thus live primarily in the photic zone; the vast majority, however, are not light dependent.

For reasons related mainly to food supply, most planktic foraminifers live in the upper 300 m of the water column, although after death, their tests fall to the underlying, deeper seafloor.

Foraminifers can be major rock forming elements in open- or restricted-shelf as well as deeper marine deposits. In some cases, foraminiferal abundances reach tens of thousands of individuals per m3 of sediment.

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