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Micro- and nanostructures of calcareous foraminiferal tests; insight from representatives of Miliolida, Rotaliida and Lagenida

Zofia Dubicka, Krzysztof Owocki and Michal Gloc
Micro- and nanostructures of calcareous foraminiferal tests; insight from representatives of Miliolida, Rotaliida and Lagenida
Journal of Foraminiferal Research (April 2018) 48 (2): 142-155

Abstract

The test structures of Lagenida, Rotaliida, and Miliolida (Foraminifera) are described at an unprecedented scale of resolution. Observations using conventional and field-emission scanning electron microscopy revealed distinct micro- and nanoscale differences in the textural compositions of these three main groups of calcifying foraminifers, consistent with recent molecular phylogenetic reconstructions and a higher-level taxonomic system. The rotaliid test is entirely composed of roughly spherical primary carbonate nanograins, up to 100 nm in diameter, which merge into micrometer-sized irregular aggregates. The miliolid test is made up of two morphologically different primary crystallites. Arbitrarily arranged needle-shaped elements (up to 1 mu m in length and 200 nm in width) make up the bulk of the test, including the inside of the wall (porcelain) and mineralized inner surface (intrados) (ca. 100 nm in thickness). Roughly spherical nanograins (up to 50 nm in diameter) form more or less regularly arranged polygons of an outer lamina (extrados), which is ca. 200 nm in thickness. By contrast, the lagenid test texture is characterized by much larger crystals than in other calcifying foraminifers. At moderate magnification, lagenid tests display a fibrous texture composed of fiber bundles (tens of mu m in length and several mu m in width) that are oriented perpendicular to test surfaces and taper towards the ends when in contact with another lamina. At higher magnification, each bundle constitutes a single calcite crystal with an inner pore extending along the entire length of the crystal/fiber. We measured test hardness using the nanoindentation method. This is the first application of this technique in microfossils. We found that Cretaceous Lagenida tests were more resistant to mechanical stress than Rotaliida tests. These comparative strengths may be linked to internal test microstructure and play a role in determining habitats in which these taxa can live.


ISSN: 0096-1191
EISSN: 1943-264X
Coden: JFARAH
Serial Title: Journal of Foraminiferal Research
Serial Volume: 48
Serial Issue: 2
Title: Micro- and nanostructures of calcareous foraminiferal tests; insight from representatives of Miliolida, Rotaliida and Lagenida
Affiliation: University of Warsaw, Faculty of Geology, Warsaw, Poland
Pages: 142-155
Published: 201804
Text Language: English
Publisher: Cushman Foundation for Foraminiferal Research, Ithaca, NY, United States
References: 88
Accession Number: 2018-059535
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, 5 plates
S32°17'60" - S32°17'60", E115°40'60" - E115°40'60"
N51°07'60" - N51°07'60", E23°28'60" - E23°28'60"
Secondary Affiliation: Polish Academy of Sciences, Institute of Paleobiology, POL, PolandWarsaw University of Technology, POL, Poland
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, Copyright, Cushman Foundation for Foraminiferal Research. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2018
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