Foraminifera

The earliest known reference to foraminifera comes from Herodotus, who in the 5th century BCE noted them as making up the rock that forms the Great Pyramid of Giza. These are today recognized as representatives of the genus Nummulites. Strabo, in the 1st Century BCE, noted the same foraminifera, and suggested that they were the remains of lentils left by the workers who built the pyramids. Robert Hooke observed a foraminifera under the microscope, as described and illustrated in his 1665 book Micrographia:I was trying several small and single Magnifying Glasses, and casually viewing a parcel of white Sand, when I perceiv'd one of the grains exactly shap'd and wreath'd like a Shell[...] I view'd it every way with a better Microscope and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell[...]Antonie van Leeuwenhoek described and illustrated foraminiferal tests in 1700, describing them as minute cockles; his illustration is recognizable as being Elphidium. Early workers classified foraminifera within the genus Nautilus, noting their similarity to certain cephalopods. It was recognised by Lorenz Spengler in 1781 that foraminifera had holes in the septa, which would eventually grant the group its name. Spengler also noted that the septa of foraminifera arced the opposite way from those of nautili and that they lacked a nerve tube. '' Alcide d'Orbigny, in his 1826 work, considered them to be a group of minute cephalopods and noted their odd morphology, interpreting the pseudopodia as tentacles and noting the highly reduced (in actuality, absent) head. He named the group foraminifères, or "hole-bearers", as members of the group had holes in the divisions between compartments in their shells, in contrast to nautili or ammonites. Cushman's scheme nevertheless remained the dominant scheme of classification until Tappan and Loeblich's 1964 classification, which placed foraminifera into the general groupings still used today, based on microstructure of the test wall. ==Taxonomy==

}} }} }} }} }} }} }} The taxonomic position of the Foraminifera has varied since Schultze in 1854, who referred to as an order, Foraminiferida. Loeblich (1987) and Tappan (1992) reranked Foraminifera as a class as it is now commonly regarded. The Foraminifera have typically been included in the Protozoa, or in the similar Protoctista or Protist kingdom. Compelling evidence, based primarily on molecular phylogenetics, exists for their belonging to a major group within the Protozoa known as the Rhizaria. ==Anatomy==

The most striking aspect of most foraminifera are their hard shells, or tests. These may consist of one of multiple chambers, and may be composed of protein, sediment particles, calcite, aragonite, or (in one case) silica. Unlike other shell-secreting organisms, such as molluscs or corals, the tests of foraminifera are located inside the cell membrane, within the protoplasm. The organelles of the cell are located within the of the test, and the of the test allow the transfer of material from the pseudopodia to the internal cell and back. The foraminiferal cell is divided into granular endoplasm and transparent ectoplasm from which a pseudopodial net may emerge through a single opening or through many perforations in the test. Individual pseudopods characteristically have small granules streaming in both directions. Foraminifera are unique in having granuloreticulose pseudopodia; that is, their pseudopodia appear granular under the microscope; these pseudopodia are often elongate and may split and rejoin each other. These can be extended and retracted to suit the needs of the cell. The pseudopods are used for locomotion, anchoring, excretion, test construction and in capturing food, which consists of small organisms such as diatoms or bacteria. The nuclei are not necessarily confined to one chamber in multi-chambered species. Nuclei can be spherical or have many lobes. Nuclei are typically 30-50 μm in diameter. Some species of foraminifera have large, empty vacuoles within their cells; the exact purpose of these is unclear, but they have been suggested to function as a reservoir of nitrate. == Ecology ==

, (22) Globorotalia inflata, (23) Globorotalia menardii, (24) Globorotalia scitula, (25) Globorotalia crassaformis, (26) Globorotalia truncatulinoides, (27) Candeina nitida, (28) Globigerinita glutinata, (29) Globigerinita uvula, and (30) Tenuitella fleisheri''. Modern Foraminifera are primarily marine organisms, but living individuals have been found in brackish, freshwater Benthic foraminifera are typically found in fine-grained sediments, where they actively move between layers; however, many species are found on hard rock substrates, attached to seaweeds, or sitting atop the sediment surface. Further, it has been suggested that some Jurassic fossil foraminifera may have also independently evolved a planktonic lifestyle, and may be members of Robertinida. A number of forams, both benthic and planktonic, have unicellular algae as endosymbionts, from diverse lineages such as the green algae, red algae, golden algae, diatoms, and dinoflagellates. Some forams are kleptoplastic, retaining chloroplasts from ingested algae to conduct photosynthesis. Most foraminifera are heterotrophic, consuming smaller organisms and organic matter; some smaller species are specialised feeders on phytodetritus, while others specialise in consuming diatoms. Some benthic forams construct feeding cysts, using the pseuodopodia to encyst themselves inside of sediment and organic particles. One group, the xenophyophores, has been suggested to farm bacteria within their tests, although studies have failed to find support for this hypothesis. Suspension feeding is also common in the group, and at least some species can take advantage of dissolved organic carbon. Certain benthic foraminifera have been found to be capable of surviving anoxic conditions for over 24 hours, indicating that they are capable of selective anaerobic respiration. This is interpreted as an adaptation to survive changing oxygenic conditions near the sediment-water interface. Foraminifera are found in the deepest parts of the ocean such as the Mariana Trench, including the Challenger Deep, the deepest part known. At these depths, below the carbonate compensation depth, the calcium carbonate of the tests is soluble in water due to the extreme pressure. The Foraminifera found in the Challenger Deep thus have no carbonate test, but instead have one of organic material. Nonmarine foraminifera have traditionally been neglected in foram research, but recent studies show them to be substantially more diverse than previously known. They are known to inhabit disparate ecological niches, including mosses, rivers, lakes and ponds, wetlands, soils, peat bogs, and sand dunes. == Reproduction ==

The generalized foraminiferal life-cycle involves an alternation between haploid and diploid generations, although they are mostly similar in form. The haploid or gamont initially has a single nucleus, and divides to produce numerous gametes, which typically have two flagella. The diploid or agamont is multinucleate, and after meiosis divides to produce new gamonts. Multiple rounds of asexual reproduction between sexual generations are not uncommon in benthic forms. ==Tests==

Foraminiferal tests serve to protect the organism within. Owing to their generally hard and durable construction (compared to other protists), the tests of foraminifera are a major source of scientific knowledge about the group. Openings in the test that allow the cytoplasm to extend outside are called apertures. The primary aperture, leading to the exterior, take many different shapes in different species, including but not limited to rounded, crescent-shaped, slit-shaped, hooded, radiate (star-shaped), dendritic (branching). Some foraminifera have "toothed", flanged, or lipped primary apertures. There may be only one primary aperture or multiple; when multiple are present, they may be clustered or equatorial. In addition to the primary aperture, many foraminifera have supplemental apertures. These may form as relict apertures (past primary apertures from an earlier growth stage) or as unique structures. Test shape is highly variable among different foraminifera; they may be single-chambered (unilocular) or multi-chambered (multilocular). In multilocular forms, new chambers are added as the organism grows. A wide variety of test morphologies is found in both unilocular and multilocular forms, including spiraled, serial, and milioline, among others. and many marine sediments are composed primarily of them. For instance, the limestone that makes up the pyramids of Egypt is composed almost entirely of nummulitic benthic Foraminifera. It is estimated that reef Foraminifera generate about 43 million tons of calcium carbonate per year. Genetic studies have identified the naked amoeba Reticulomyxa and the peculiar xenophyophores as foraminiferans without tests. A few other amoeboids produce reticulose pseudopods, and were formerly classified with the forams as the Granuloreticulosa, but this is no longer considered a natural group, and most are now placed among the Cercozoa. == Evolutionary history ==

Molecular clocks indicate that the crown-group of foraminifera likely evolved during the Neoproterozoic, between 900 and 650 million years ago; this timing is consistent with Neoproterozoic fossils of the closely related filose amoebae. As fossils of foraminifera have not been found prior to the very end of the Ediacaran, it is likely that most of these Proterozoic forms did not have hard-shelled tests. Due to their non-mineralised tests, "allogromiids" have no fossil record. However, the discovery of diagenetically altered C27 sterols associated with the remains of Dickinsonia cast doubt on this identification and suggest it may instead be an animal. Other researchers have suggested that the elusive trace fossil Paleodictyon and its relatives may represent a fossil xenophyophore and noted the similarity of the extant xenophyophore Occultammina to the fossil; however, modern examples of Paleodictyon have not been able to clear up the issue and the trace may alternately represent a burrow or a glass sponge. Supporting this notion is the similar habitat of living xenophyophores to the inferred habitat of fossil graphoglyptids; however, the large size and regularity of many graphoglyptids as well as the apparent absence of xenophyae in their fossils casts doubt on the possibility. Test-bearing foraminifera have an excellent fossil record throughout the Phanerozoic eon. The earliest known definite foraminifera appear in the fossil record towards the very end of the Ediacaran; these forms all have agglutinated tests and are unilocular. These include forms like Platysolenites and Spirosolenites. The earliest multi-chambered foraminifera are agglutinated species, and appear in the fossil record during the middle Cambrian period. Due to their poor preservation they cannot be positively assigned to any major foram group. Later species of fusulinids grew to much larger size, with some forms reaching 5 cm in length; reportedly, some specimens reach up to 14 cm in length, making them among the largest foraminifera extant or extinct. Fusulinids are the earliest lineage of foraminifera thought to have evolved symbiosis with photosynthetic organisms. Fossils of fusulinids have been found on all continents except Antarctica; they reached their greatest diversity during the Visean epoch of the Carboniferous. The group then gradually declined in diversity until finally going extinct during the Permo-Triassic extinction event. During the Tournaisian epoch of the Carboniferous, Miliolid foraminifera first appeared in the fossil record, having diverged from the spirillinids within the Tubothalamea. Miliolids suffered about 50% casualties during both the Permo-Triassic and K-Pg extinctions but survived to the present day. Some fossil miliolids reached up to 2 cm in diameter. Diversity of the group remained low until the aftermath of the Cenomanian-Turonian event, after which the group saw a rapid diversification. Of this group, the planktonic Globigerinina—the first known group of planktonic forams—first appears in the aftermath of the Toarcian Turnover; the group saw heavy losses during both the K-Pg extinction and the Eocene-Oligocene extinction, but remains extant and diverse to this day. An additional evolution of planktonic lifestyle occurred in the Miocene or Pliocene, when the rotaliid Neogallitellia independently evolved a planktonic lifestyle. ==Paleontological applications==

Dying planktonic Foraminifera continuously rain down on the sea floor in vast numbers, their mineralized tests preserved as fossils in the accumulating sediment. Beginning in the 1960s, and largely under the auspices of the Deep Sea Drilling, Ocean Drilling, and International Ocean Drilling Programmes, as well as for the purposes of oil exploration, advanced deep-sea drilling techniques have been bringing up sediment cores bearing Foraminifera fossils. The effectively unlimited supply of these fossil tests and the relatively high-precision age-control models available for cores has produced an exceptionally high-quality planktonic Foraminifera fossil record dating back to the mid-Jurassic, and presents an unparalleled record for scientists testing and documenting the evolutionary process. Because certain types of foraminifera are found only in certain environments, their fossils can be used to figure out the kind of environment under which ancient marine sediments were deposited; conditions such as salinity, depth, oxygenic conditions, and light conditions can be determined from the different habitat preferences of various species of forams. This allows workers to track changing climates and environmental conditions over time by aggregating information about the foraminifera present. In other cases, the relative proportion of planktonic to benthic foraminifera fossils found in a rock can be used as a proxy for the depth of a given locality when the rocks were being deposited. s from Paleocene-Eocene Thermal Maximum (PETM) sediments in southern Maryland. The scale bars measure 150 microns (0.015 cm). Each specimen is similar in size to a grain of sand. composition of benthic foraminifera. The Paleocene-Eocene thermal maximum is characterized by a brief but prominent excursion, attributed to rapid warming. Since at least 1997, the Paleocene–Eocene thermal maximum (PETM) has been investigated as an analogy for understanding the effects of global warming and of massive carbon inputs to the ocean and atmosphere, including ocean acidification. Humans today emit about 10 Gt of carbon (about 37 Gt CO2e) per year, and at that rate will release a comparable amount to the PETM in about one thousand years. A main difference is that during the PETM the planet was ice-free, as the Drake Passage had not yet opened and the Central American Seaway had not yet closed. Although the PETM is now commonly held to be a case study for global warming and massive carbon emission, the cause, details, and overall significance of the event remain uncertain. This application of foraminifera was discovered by Alva C. Ellisor in 1920. of a peneroplid foraminiferan from Holocene lagoonal sediment in Rice Bay, San Salvador Island, Bahamas. Scale bar 100 micrometres Calcareous fossil foraminifera are formed from elements found in the ancient seas where they lived. Thus, they are very useful in paleoclimatology and paleoceanography. They can be used, as a climate proxy, to reconstruct past climate by examining the stable isotope ratios and trace element content of the shells (tests). Global temperature and ice volume can be revealed by the isotopes of oxygen, and the history of the carbon cycle and oceanic productivity by examining the stable isotope ratios of carbon; see δ18O and δ13C. The concentration of trace elements, like strontium (Sr), magnesium (Mg), lithium (Li) and boron (B), also hold a wealth of information about global temperature cycles, continental weathering, and the role of the ocean in the global carbon cycle. Geographic patterns seen in the fossil records of planktonic forams are also used to reconstruct ancient ocean currents. ==Modern uses==

The oil industry relies heavily on microfossils such as forams to find potential hydrocarbon deposits.'', a benthic foram from the North Sea. For the same reasons they make useful biostratigraphic markers, living foraminiferal assemblages have been used as bioindicators in coastal environments, including indicators of coral reef health. Because calcium carbonate is susceptible to dissolution in acidic conditions, foraminifera may be particularly affected by changing climate and ocean acidification. Foraminifera have many uses in petroleum exploration and are used routinely to interpret the ages and paleoenvironments of sedimentary strata in oil wells. Agglutinated fossil foraminifera buried deeply in sedimentary basins can be used to estimate thermal maturity, which is a key factor for petroleum generation. The Foraminiferal Colouration Index (FCI) is used to quantify colour changes and estimate burial temperature. FCI data is particularly useful in the early stages of petroleum generation (about 100 °C). Foraminifera can also be used in archaeology in the provenancing of some stone raw material types. Some stone types, such as limestone, are commonly found to contain fossilised foraminifera. The types and concentrations of these fossils within a sample of stone can be used to match that sample to a source known to contain the same "fossil signature". ==Gallery==

File:3339c Croatie Pag.jpg|Foraminifera of Pag Island, Adriatic Sea -60 m, field width 5.5 mm File:3339d Croatie Pag.jpg|Foraminifera of Pag Island, Adriatic Sea -60 m, field width 5.5 mm File:3339e Croatie Pag.jpg|Foraminifera of Pag Island, Adriatic Sea -60 m, field width 5.5 mm File:3339f Croatie Pag.jpg|Foraminifera of Pag Island, Adriatic Sea -60 m, field width 5.5 mm File:2966g Bali.jpg|Foraminifera of Indian Ocean, south-eastern coast of Bali, field width 5.5 mm File:2966j Bali.jpg|Foraminifera of Indian Ocean, south-eastern coast of Bali, field width 5.5 mm File:2966k Bali.jpg|Foraminifera of Indian Ocean, south-eastern coast of Bali, field width 5.5 mm File:Foraminifères de Ngapali.jpg|Foraminifera in Ngapali, Myanmar, field width 5.22 mm File:3579h R Indonesie.jpg|Foraminifera Heterostegina depressa, field width 4.4 mm ==See also==