The Foraminifera are Protozoaire S appeared with the Cambrien. The test (sometimes baptized, wrongly, shell ), including/understanding one or more rooms (or loculus or cabins ), is provided with one or more foramen (opening). They have a benthic lifestyle (on and in the sediment) or planktonique (in the water column, and particularly in the photic Zone). Their size generally varies from 38 µm with 1 mm (some can make more than 10 cm). Their food mode consists of Bactérie S, of Algue S, larvae of Mollusque S, Crustacé S, varied waste.

History of their discovery

It is in 1826 that Alcide Dessalines d' Orbigny (1802 - 1857) creates the order of Foraminifera in a work entitled methodical Tableau of the class of the Céphalopode S . During its life, Orbigny, will describe 1  500 species, the majority news for science. It was the first studied their lifestyle and the ecological requirements. But the unicellular nature of Foraminifera was discovered by Felix Dujardin (1801 - 1860) in 1835. It is thanks to their study that he discovers the Protoplasme organizations Unicellulaire S.

Bases of classification

The composition of this test (organic, bound, carbonated and siliceous) is the principal criterion of classification of Foraminifera and is at the base of the majority of classifications, of which that of Loeblich and Tappan (1964 and 1988). Foraminifera with organic tests are mainly represented by unilocular Foraminifera, Allogromiina (sub-order). This sub-order is still badly known since, because of its loss in the fossil assemblies, the micropaleontologists studied them very little. However, currently, the Gooday group, in Southampton (the United Kingdom) tries to fill the delay, at least, on their recognition. Foraminifera with aggluttinés tests are characterized by the agglutinat grains taken in the sediment (cf Gaudryina sp., foraminifère in bottom on the left on the board proposed). A selection of the grains could take place at certain species (e.g. Saccammina micaceus , which presents only grains of micas). Two types of Foraminifera to carbonated tests can be differentiated. Porcelanés have an opaque white aspect, whereas the hyaline ones are transparent and vitreous. Lastly, Foraminifera with siliceous tests are extremely rare. The second criterion of classification is the fitting of the cabins. Thus, one can distinguish several great types of tests:

  • unilocular tests;
  • plurilocular tests:
    • seriated tests, the cabins are organized in series (e.g. Gaudryina sp.);
    • spiral tests (the made-to-order of snails; three other examples on the board);
    • discoidal tests;
    • tests milioliformes. The cabins are formed successively and individually in several plans;
    • complex tests.
A third criterion is the ornamentation of the test. The test can be smooth, but often presents outgrowths (coasts, spines, suturaux bridges…) and of the depressions. Lastly, a fourth criterion is the morphology of the principal opening and its position. Thus, the opening is sometimes in relation to additional elements (teeth, lips, plates…) and/or at the end of a coll.

Potential use of recent Foraminifera

Omnipresent in the seamen circles, they occupy of very many ecological niches (maritime marshes with the abyssal plains). Because of their life cycle runs (1 to 3 months on average, 1 maximum year), Foraminifera react quickly to the changes of their environment. Their populations can grow or decrease, their variety to change, the cabins to grow or be reduced… The environmental pollution and changes (e.g climatic variations) can thus lead to a radical transformation of the populations of Foraminifera. Thus, their life cycle runs and their ubiquity in the seamen circle, associated with a great richness in the sediment (robust statistical analyzes), a not very expensive and easy method of analysis and with a trace in the fossil (the study allows before modification of the medium) make Foraminifera, in particular benthic, of good biological indicators of or the proxies environmental quality of the environmental changes.

Foraminifera in paleontology

Foraminifera are excellent biostratigraphic markers . They are used in Géologie for the dating of the sedimentary rocks.
Certain rocks are made up mainly of an accumulation of Foraminifera (stone with black poplars of the Stampien of Seine-et-Marne, made up of nummulites; sand Villiers-Saint-Frederic (Yvelines) composed of Milliole S from 1 to 2 mm accumulated by the wind; etc).

The order of Foraminifera (Foraminiferida) appeared at the beginning of the Cambrien. Foraminifera are characterized by their architecture (the shape and arrangement of the rooms), and the microstructure of their test (organic, agglutination of exogenic particles, crystallization microgranulaire, porcelanée, or hyaline, of calcium carbonate).

Some data on their classification

Some S ( - ina ), S ( - acea ) and S ( - idae ) of Foraminifera:

  • the Fusulinina:
  • the Miliolina (Alveolinidae Ehrenberg, 1839);
  • the Rotaliina:
    • Rotaliacea (Rotaliidae, Nummulitidae,…) ;
    • Globigerinacae ;
    • Orbitoïdacea ;
  • the Textulariina:
    • Lituolacea (Orbitolinidae,…)
  • the Globotruncana
  • …

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