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| Foraminifera
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Allogromiida Carterinida Fusulinida - extinct Globigerinida Involutinida Lagenida Miliolida Robertinida Rotaliida Silicolocunida Spirillinida Textulariida
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300px SEM micrographs of four benthic foraminiferans (ventral view).
Clockwise from top left: Ammonia beccarii , Elphidium excavatum clavatum,
Buccella frigida , and Eggerella advena .
About 250 000 species are recognized, some living and some fossil, and they make up an important part of many marine sediments. Some are known as far back as the Cambrian period. The form of the test is the primary means by which foraminferans are identified and classified. Nummulitic limestone, which makes up the pyramids of Egypt, is almost entirely ancient foraminifera.
A few other amoeboids produce reticulose pseudopods but lack elaborate tests, and these have been considered possible relatives of the foraminiferans, grouped together as the Granuloreticulosa. However, with the exception of Reticulomyxa, shown by genetic studies to be a foraminiferan that has lost its shell, their affinities appear to lie elsewhere. Several are placed among the Cercozoa, a diverse group closely related to the true foraminiferans. Both these groups are included among the Rhizaria.
A number of foraminifera have developed endosymbiotic interactions with unicellular algae. Their endosymbionts span divergent lineages such as the green algae, red algae, dinoflagellates, chrysophytesThe golden algae or chrysophytes are a large group of heterokont algae, found mostly in freshwater. Originally they were taken to include all such forms except the diatoms and multicellular brown algae, but since then they have been divided into several d, and diatoms. Some sequester chloroplastChloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. Chloroplasts are similar to mitochondria but are found only in plants. Both organelles are surrounded by a double membrane with an intermembrane space; bots of the algae they feed upon, and gain food from photosynthesisPhotosynthesis is a biochemical process in which plants, green algae, and some bacteria use the energy of light to combine water and carbon dioxide into oxygen and energy. It nourishes nearly all living things directly or indirectly, making it vital to li in these stolen chloroplasts, a condition known as kleptoplasty .