Foraminifera test
Foraminiferal tests are the tests (or shells) of Foraminifera.
Foraminifera (forams for short) are single-celled predatory protists, mostly marine, and usually protected with shells. These shells, often called tests, can be single-chambered or have multiple interconnected chambers; the cellular machinery is contained within the shell. So important is the test to the biology of foraminifera that it provides the scientific name of the group—foraminifera, Latin for "hole bearers", referring to the pores connecting chambers of the shell in the multi-chambered species.
Foraminiferal tests are usually made of calcite, a form of calcium carbonate (CaCO
3), but are sometimes made of aragonite, agglutinated sediment particles, chitin, or (rarely) of silica.[1] Other foraminifera lack tests altogether.[2]
Over 50,000 species are recognized, both living (6,700 - 10,000)
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Background
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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.[10] 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.[11]
Many foraminifera exhibit dimorphism in their tests, with microspheric and megalospheric individuals. These names should not be taken as referring to the size of the full organism; rather, they refer to the size of the first chamber, or proloculus. Tests as fossils are known from as far back as the Ediacaran period,[12] 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.[13] It is estimated that reef foraminifera generate about 43 million tons of calcium carbonate per year.[14]
Genetic studies have identified the naked amoeba
Composition
The form and composition of their tests are the primary means by which forams are identified and classified. Most secrete calcareous tests, composed of calcium carbonate.[16] Calcareous tests may be composed of either aragonite or calcite depending on species; among those with calcite tests, the test may contain either a high or low fraction of magnesium substitution.[17] The test contains an organic matrix, which can sometimes be recovered from fossil samples.[17]
Some studies suggest a high amount of homoplasy in foraminifera, and that neither agglutinated nor calcareous foraminifera form monophyletic groupings.[18]
Soft
In some forams, the tests may be composed of organic material, typically the protein tectin. Tectin walls may have sediment particles loosely adhered onto the surface.[11] The foram Reticulomyxa entirely lacks a test, having only a membranous cell wall.[2] Organic-walled forams have traditionally been grouped as the "allogromiids"; however, genetic studies have found that this does not make up a natural group.[18]
Agglutinated
Other forams have tests made from small pieces of sediment cemented together (agglutinated) by either proteins (possibly collagen-related), calcium carbonate, or Iron (III) oxide.[11][19] In the past these forms were grouped together as the single-chambered "astrorhizids" and the multi-chambered textulariids. However, recent genetic studies suggest that "astrorhizids" do not make up a natural grouping, instead forming a broad base of the foram tree.[18]
Textulariid foraminifera, unlike other living members of the globothalamea, have agglutinated tests; however, grains in these tests are cemented with a calcite cement. This calcite cement is made up of small (<100 nm) globular nanograins, similar to in other globothalameans. These tests may also have many pores, another feature uniting them with the globothalamea.[20]
Agglutinating foraminifera may be selective regarding what particles they incorporate into their shells. Some species prefer certain sizes and types of rock particles; other species are preferential towards certain biological materials. Certain species of foraminifera are known to have preferentially agglutinated coccoliths to form their tests; others preferentially utilise echinoderm plates, diatoms, or even other foraminiferans' tests.[21]
The foraminifera Spiculosiphon preferentially agglutinates silica sponge spicules using an organic cement; it shows strong selectivity also towards shape, utilising elongated spicules on its "stalk" and shortened ones on its "bulb". It is thought to use the spicules as both a means of elevating itself off the seabed as well as to lengthen the reach of its pseudopodia to capture prey.[19]
The agglutinated tests of xenophyophores are the largest of any foraminifera, reaching up to 20 cm in diameter. The name "xenophyophore", meaning "bearer of foreign bodies", refers to this agglutinating habit. Xenophyophores selectively uptake sediment grains between 63 and 500 µm, avoiding larger pebbles and finer silts; type of sediment seems to be a strong factor in which particles are agglutinated, as particle type preferentially includes sulfides, oxides, volcanic glass, and especially tests of smaller foraminifera. Xenophyophores 1.5 cm in diameter have been recorded completely naked, with no test whatsoever.[22]
Calcareous
Of those foraminifera with calcareous tests, several different structures of calcite crystals are found.
Porcelaneous
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section showing chambers of a spiral foram
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Live Ammonia tepida streaming granular ectoplasm for catching food
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Group of planktonic forams
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Fossil nummulitid forams of various sizes from the Eocene
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TheEgyptian pyramids were constructed from limestone that contained nummulites.[32]
References
- ISBN 978-0-87933-070-5.
- ^ S2CID 36497475.
- S2CID 24388876.
- ^ Ald, S.M. et al. (2007) Diversity, Nomenclature, and Taxonomy of Protists, Syst. Biol. 56(4), 684–689, DOI: 10.1080/10635150701494127.
- ^ Pawlowski, J., Lejzerowicz, F., & Esling, P. (2014). Next-generation environmental diversity surveys of foraminifera: preparing the future. The Biological Bulletin, 227(2), 93–106.
- ^ "World Foraminifera Database".
- ^ Marshall M (3 February 2010). "Zoologger: 'Living beach ball' is giant single cell". New Scientist.
- ISBN 978-3-540-96815-3.
- ^ Wassilieff, Maggy (2006) "Plankton – Animal plankton", Te Ara – the Encyclopedia of New Zealand. Accessed: 2 November 2019.
- .
- ^ ISBN 978-3-319-14574-7
- ISSN 1068-7971.
- ^ Foraminifera: History of Study, University College London, retrieved 20 September 2007
- .
- S2CID 8060916.
- OCLC 9276403.
- ^ ISBN 978-0-306-48104-8
- ^ ISSN 0377-8398.
- ^ PMID 26312358.
- ^ ISSN 0567-7920.
- ISSN 0096-1191.
- ISSN 0198-0149.
- S2CID 242629553
- ^ ISSN 0096-1191.
- ^ ISBN 978-0-306-48104-8
- PMID 29123221.
- ISSN 1809-127X.
- ISSN 0096-1191.
- ISBN 978-1-4020-0598-5.
- ^ Resig, J; Lowenstam, H; Echols, R; Weiner, S (1980). "An extant opaline foraminifer: test ultrastructure, mineralogy, and taxonomy". Special Publications of the Cushman Foundation for Foraminiferal Research. 19: 205–214.
- ^ Favulina hexagona European Geosciences Union, 9 November 2020.
- ^ Foraminifera: History of Study, University College London. Retrieved: 18 November 2019.