Overview

Brief Summary

The Foraminifera, often called forams, are an ancient taxonomic group (sometimes considered a phylum, sometimes subphylum or class of Kingdom Rhizaria) of amoeboid, single-celled Eukaryotes.  They have a fossil record back to the earliest Cambrian, 570 million years ago.  Most Foraminifera live in benthic environments (ocean floors) although planktonic forams appeared in the fossil record starting about 170 million years ago and about 1% of known extant species live in the water column.  Foraminifera are traditionally considered marine organisms, indeed, in many marine environments they are the most abundant shelled organism.  Expert scientists estimate approximately 6000 described and about 1500 yet unknown marine foram species (Appeltans et al. 2012).  However, recent molecular studies challenge the idea that Foraminifera are almost entirely marine, through descriptions of multiple new foram groups representing multiple colonizations of freshwater environments (Holzmann et al. 2003), and new species that suggest diverse and abundant foraminiferan life in terrestrial soils (Lejzerowicz et al. 2010).

Most forams have an external shell, the composition and shape of which is the primary determiner of foraminiferan taxonomy.  Because the organism’s protoplasm often covers it, the shell is referred to as a test.  Foram tests are composed of one of three different materials: secreted calcium carbonate or silica; secreted polysaccharides; or glued-together particles, such as quartz sand grains, sponge spicules, or other available building blocks that are the right size.  In most species the test is multi-chambered, and Foraminifera get their name from the tiny openings (foramina) between the chambers.  As they grow, Foraminifera build on more chambers, expanding to live in all of them except the one or two most recently built.  A broad diversity of chamber arrangement and many types and placements of aperture (the terminal opening to the outside of the test) define the test morphology, which can be quite beautiful and complex.  Some resembling mollusk and bivalve shells caused early taxonomists to believe foraminifera shared a lineage with the mollusks (Korsun et al. 2001; Olney 2002; Wetmore 1995).

While most foraminiferan species have a maximum size between 0.05-0.7 mm, some species grow much larger.  One of the largest extant species, Cycloclypeus carpenteri, (Nummulitidae) measures over 10 cm across its disc-like test; another extant species, Syringammina fragilissima (Xenophyophorea) is documented up to 20 cm and looks like a porous beach ball made of sand.  The fossil record shows a diversity of even larger species.  Even the largest Foraminifera are single-celled, however they may have multiple nuclei (Krüger 1997; Pawlowski 2003; Song et al. 1994).

Some of the largest species form symbiotic associations with algal cells.  Xenophyophoreans are thought to cultivate bacteria for food.  Other species are suspension feeders, opportunistic omnivores that eat detritus, smaller protists and even multicellular organisms from the substrate.  To reduce issues of high with surface area to volume ratios, forams have thin pseudopodia (called reticulopodia) which stretch out of tiny pores in the test, to dramatically extend their surface area.  Some stretch their long pseudopodia to form a large external feeding net, and they can also use their pseudopodia to burrow through the sediment or to attach themselves to rocks or plants efficiencies (Korsun et al. 2001; Olney 2002; Wetmore 1995).  

Foraminiferan species are found all over the world and species tend to be particular to their specific environment, for example, deep sea trenches, intertidal pools, coral reefs, brackish estuaries.  They can be extremely abundant, in some places in the deep sea the sediment on the sea floor is composed almost entirely of shells from planktonic species.  Forams are an important basic link in the marine food chain, as food for small invertebrates and fish.  Because they are so wide-spread and ancient in origin, fossil Foraminifera are useful for analyzing changes throughout time in ocean environments and temperatures and predicting climate changes.  They are used as bioindicators of the health of marine environments, including coral reefs.  The oil industry analyses forams deposits as they give precise indicators of age and conditions of rock formation important in guiding drilling for opimum oil well efficiencies (Korsun et al. 2001; Olney 2002; Smithsonian NMNH 2013; Wetmore 1995). 

A recent study compared Foraminiferan species diversity in deep sea environments (>1500m) around the world and found that species numbers, composition and genetic makeup was far more consistent among deep sea sampling locations than numbers and composition of foram species in different shallow habitats (<200 m), revealing greater stasis of species over space and time at depth.  Along with observations that deep sea species have a longer duration in the fossil record than do shallow species, they propose that a model where new species evolve in shallower areas and then migrating to deeper seas seems to be consistent with marine foram samplings (Buzas et al. 2013).

  • Appeltans, C. et al. (>100 authors), 2012. The Magnitude of Global Marine Species Diversity. Current Biology, Volume 22, Issue 23, 2189-2202, 15 November 2012. 10.1016/j.cub.2012.09.036
  • Buzas, M.A., L.C. Hayek, S.J. Culver, B.W. Hayward, and L.E. Osterman, 2013. Ecological and evolutionary consequences of benthic community stasis in the very deep sea (>1500 m). Paleobiology : 102-12. http://dx.doi.org/10.1666/13010
  • HOLZMANN, M., HABURA, A., GILES, H., BOWSER, S. S. and PAWLOWSKI, J. (2003), Freshwater Foraminiferans Revealed by Analysis of Environmental DNA Samples. Journal of Eukaryotic Microbiology, 50: 135–139. doi: 10.1111/j.1550-7408.2003.tb00248.x
  • Korsun, S., Polyak, L. and Febo, L. 2001. Foraminiferal research at Byrd Polar Research Center. Retrieved December 6 2013 from http://bprc.osu.edu/geo/projects/foram/whatarefor.htm
  • Krüger, R.; Röttger, R.; Lietz, R., and J. Hoheneggerz, 1997. Biology and reproductive processes of the larger foraminiferan Cycloclypeus carpenteri (Protozoa, Nummulitidae), Archiv für Protistenkunde, Volume 147, Issues 3–4, Pages 307-321, ISSN 0003-9365, http://dx.doi.org/10.1016/S0003-9365(97)80057-7.
  • Lejzerowicz, F., Pawlowski, J., Fraissinet-Tachet, L. and Marmeisse, R. (2010), Molecular evidence for widespread occurrence of Foraminifera in soils. Environmental Microbiology, 12: 2518–2526. doi: 10.1111/j.1462-2920.2010.02225.x
  • Olney, M. 2002. Foraminifera. MIRACLE: Microfossil image recovery and circulation for learning and education. University College London, Micropalaeontology Unit. U.K. Retrieved December 6 2013 from http://www.ucl.ac.uk/GeolSci/micropal/foram.html#largerbenthicimages.
  • Pawlowski J, Holzmann M, Fahrni J, Richardson SL. (2003). Small subunit ribosomal DNA suggests that the xenophyophorean Syringammina corbicula is a foraminiferan. Journal of Eukaryotic Microbiology 50(6): 483-7.
  • Smithsonian National Museum of Natural History, 2013. Joseph Augustine Cushman, Department of Paleontology. Retrieved December 9, 2013 from http://paleobiology.si.edu/cushman/index.html.
  • Song, Y.; Black, R.G. and J.H. Lipps. 1994. Morphological Optimization in the Largest Living Foraminifera: Implication from Finite Element Analysis. Paleobiology 20(1):14-26.
  • Wetmore, K.L. 1995. Foraminifora. University of California Museum of Paleontology. Retrieved December 9, 2013 from http://www.ucmp.berkeley.edu/foram/foramfr.html and sister pages.
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Comprehensive Description

Description of Foraminiferida

Granuloreticulosea, with shells (loricae); among the more abundant and most conspicuous protozoa in most marine and brackish water habitats; shells may be durable and are an important component of marine sediments and fossilize well; good geological record extending back to the Cambrian, planktonic more commonly benthic; large protozoa (range 60 µm-12 cm), life-spans often proportional to their sizes (days-years); some monothalamic species reproduce by binary fission, budding, or cytotomy; most have complex life cycles, involving both sexual and asexual reproduction; there may be morphological differences between the sexual (gamont) and asexual (agamont, schizont) phases of the life cycles; the materials used in the test (e.g. organic, agglutinated, various types of mineralized calcareous), the geometry of chambers (in multichambered species) and their construction, the form of the aperture(s) are some of the important characters used in foraminiferan identification and classification.; planktonic foraminifera are often hosts for endosymbiotic algae.
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Physical Description

Diagnostic Description

Diagnostic Apomorphies of Foraminifera

The diagnostic apomorphies of Foraminifera include both morphological and molecular characters.  One of the most recognizable apomorphies that characterizes the derived foraminiferal subclades, is the presence of a test, or shell, that grows by terminal addition, either by the addition of discrete chambers (resulting in a multi-chambered test), or by accretionary growth whereby new material is added to the test at the apertural margin of a single-chambered tubular test (Goldstein 2002, Hottinger 2000). 

Additional apomorphies can only be observed in living taxa, and thus serve to distinguish Foraminifera from other crown clades (such as Gromida, Haplosporidia, Plasmodiophorida, and Radiolaria), within the more inclusive clade Rhizaria. The small subunit ribosomal RNA sequences of foraminiferans possess a unique helix in Domain III that is up to 350 nucleotides in length, and lies between Helices 41 and 39 in Domain III, and (Bowser et al. 2008: Fig. 5.2, Habura et al. 2004: Figs. 2, 3). The gene sequences that code for the two foraminiferal actin paralogs contain twenty unique spliceosomal introns (Flakowski et al. 2006: Fig. 2).

Foraminiferans possess a type 2 ß-tubulin isoform that is highly divergent relative to other eukaryotes (Habura et al. 2005: Figs. 3, 4). The reticulopodia of foraminiferans possess motility organizing vesicles (elliptical, fuzzy-coated vesicles) (Bowser and Travis 2002: Pl. 2, figs. 1, 2), and tubulin-containing helical filaments (Bowser and Travis 2002: Pl. 2, fig. 3; Pl. 3, Habura et al. 2005: Fig. 1).

  • Bowser, S. S., A. Habura, and J. Pawlowski. 2008. Molecular evolution of Foraminifera. Pp. 78-93. In L. A. Katz, and D. Bhattacharya, eds. Genomics and Evolution of Microbial Eukaryotes. Oxford University Press, Oxford, UL.
  • Bowser, S. S., and J. L. Travis. 2002. Reticulopodia: Structural and Behavioral Basis for the Suprageneric Placement of Granuloreticulosan Protists. Journal of Foraminiferal Research 32(4):440-447.
  • Flakowski, J., I. Bolivar, J. Fahrni, and J. Pawlowski. 2006. Tempo and mode of spliceosomal intron evolution in actin of foraminifera. Journal of Molecular Evolution 63(1):30-41.
  • Goldstein, S. T. 2002. Foraminifera: A biological overview. Pp. 37-55. In B. K. Sen Gupta, ed. Modern Foraminifera. Kluwer Academic Publishers, Dordrecht and Boston.
  • Habura, A., D. R. Rosen, and S. S. Bowser. 2004. Predicted secondary structure of the foraminiferal SSU 3’ major domain reveals a molecular synapomorphy for granuloreticulosean protists. Journal of Eukaryotic Microbiology 51(4):464-471.
  • Habura, A., L. Wegener, J. L. Travis, and S. S. Bowser. 2005. Structural and functional implications of an unusual foraminiferal β-tubulin. Molecular Biology and Evolution 22(10):2000-2009.
  • Hottinger, L. C. 2000. Functional morphology of benthic foraminiferal shells, envelopes of cells beyond measure. Micropaleontology 46(Supplement 1: Advances in the Biology of Foraminifera):57-86.
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Ecology

Associations

Known predators

  • Christian RR, Luczkovich JJ (1999) Organizing and understanding a winter’s seagrass foodweb network through effective trophic levels. Ecol Model 117:99–124
  • Hall SJ, Raffaelli D (1991) Food-web patterns: lessons from a species-rich web. J Anim Ecol 60:823–842
  • Huxham M, Beany S, Raffaelli D (1996) Do parasites reduce the chances of triangulation in a real food web? Oikos 76:284–300
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Known prey organisms

Foraminifera (Foraminifera (Formaifera??)) preys on:
phytoplankton
bacterioplankton
Microprotozoa
POM

Based on studies in:
USA: Florida (Estuarine)
Scotland (Estuarine)

This list may not be complete but is based on published studies.
  • Christian RR, Luczkovich JJ (1999) Organizing and understanding a winter’s seagrass foodweb network through effective trophic levels. Ecol Model 117:99–124
  • Hall SJ, Raffaelli D (1991) Food-web patterns: lessons from a species-rich web. J Anim Ecol 60:823–842
  • Huxham M, Beany S, Raffaelli D (1996) Do parasites reduce the chances of triangulation in a real food web? Oikos 76:284–300
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Evolution and Systematics

Evolution

A recent study compared Foraminiferan species diversity in deep sea environments (>1500m) around the world and found that species numbers, composition and genetic makeup was far more consistent among deep sea sampling locations than numbers and composition of foram species in different shallow habitats (<200 m), revealing greater stasis of species over space and time at depth.  Along with observations that deep sea species have a longer duration in the fossil record than do shallow species, they propose that a model where new species evolve in shallower areas and then migrating to deeper seas where their evolutionary rate slows seems to be consistent with marine foram samplings (Buzas et al. 2013).

  • Buzas, M.A., L.C. Hayek, S.J. Culver, B.W. Hayward, and L.E. Osterman, 2013. Ecological and evolutionary consequences of benthic community stasis in the very deep sea (>1500 m). Paleobiology : 102-12. http://dx.doi.org/10.1666/13010
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Names and Taxonomy

Taxonomy

Origin of the Name Foraminifera

The name Foraminifera is a latinization of the French name Foraminifères, first applied to a group of “microscopic cephalopods” by Alcide d’Orbigny in 1826. The name is derived from the Latin foramen (hole) and -fer (bearing), so called because the aperture and openings that connect successive chambers (intercameral foramina) in a multi-chambered foraminiferal test were thought to be homologous to the siphon in the chambered Nautilus. Earlier researchers considered foraminiferans to be molluscans and classified under them under various names, such as Polythalamiis (Breyn 1732:1), Nautilus (Fichtel and Moll 1798:12), Polythalamacea (de Blainville, 1824:175) and Asiphonoidea (de Haan, 1825:29). Dujardin’s (1835a-d) discovery that foraminiferans were not cephalopods, but single-celled organisms, lead to their reclassification as rhizopods (Rhizopodes or Rhizopoda), and the reinterpretation of their “tentacles” as pseudopodia, or threadlike extensions of the cell’s sarcode or cytoplasm (Dujardin, 1841).  Ehrenberg (1838) used the name Polythalamia for the group, but viewed foraminiferans and other single-celled eukaryotes as organisms complete with miniature circulatory, digestive, excretory, nervous, motor, and reproductive systems (Churchill 1989).

  • Breyn, J. P. 1732. Dissertatio physica de Polythalamiis, nova testaceorum classe : cui quaedam praemittuntur de methodo testacea in classes et genera distribuendi : huic adiicitur commentatiuncula de Belemnitis Prussicis : tandemque schediasma de Echinis methodice disponendis. Apud Cornelium a Beughem, Gedani.
  • Churchill, F. B. 1989. The guts of the matter. Infusoria from Ehrenberg to Bütschli: 1838–1876. Journal of the History of Biology 22(2):189-213.
  • d'Orbigny, A. D. 1826. Tableau méthodique de la classe des Céphalopodes. Annales des Sciences Naturelles 7:96-169, 245-314.
  • de Blainville, H. M. D. 1824. Mollusques. Pp. 1-414. In F. Cuvier, ed. Dictionnaire des Sciences Naturelles. F. G. Levrault, Strasbourg and Paris.
  • de Haan, G. 1825. Monographiae Ammoniteorum et Goniatiteorum specimen. Lugduni Batavorum, Hazenberg.
  • Dujardin, F. 1835a. Observations nouvelles sur les prétendus Céphalopodes microscopiques. Annales des Sciences Naturelles (3):312-316.
  • Dujardin, F. 1835b. Observations nouvelles sure les Céphalopodes microscopiques. Annales des Sciences Naturelles 3:108-109.
  • Dujardin, F. 1835c. Observations sur les rhizopodes et les infusoires. Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences 1835:338-340.
  • Dujardin, F. 1835d. Recherches sur les organisms inférieurs. Annales des Sciences Naturelles 4:343-377.
  • Dujardin, F. 1841. Histoire naturelle des zoophytes. Infusoires, comprenant la physiologie et la classification de ces animaux et la maniere de les étudier à l’aide du microscope. Librairie Encyclopédique de Roret, Paris.
  • Ehrenberg, C. G. 1838. Dem blossen Auge unsichtbare Kalkthierchen und Kieselthierchen als Hauptbestand theile der Kreidegebirge. Bericht über die zur Bekanntmachung geeigneten. . Verhandlungen der Königlich Preussische Akademie der Wissenschaften zu Berlin (1838):192-200.
  • Fichtel, L. v., and J. P. C. v. Moll. 1798. Testacea microscopica aliaque minuta ex generibus Argonauta et Nautilus ad naturam picta et descripta. Anton Pichler, Vienna.
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