Wray, John L. Marathon Oil Company, Littleton, Colorado.
Last reviewed:December 2015
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A genus of fossil cyanobacteria. The extinct members of the genus Girvanella are characterized by flexuous, tubular filaments of uniform diameter, composed of thick, calcareous walls (see illustration). The external diameters of these cyanobacteria (formerly referred to as blue-green algae) average between 10 and 30 micrometers (μm), although specimens less than 10 μm and up to about 100 μm have been identified as Girvanella. Filaments may occur free (unattached), but they usually occur in groups, twisted together to form nodules and encrusting masses on various objects. The genus is intergrown with encrusting foraminifers in some Paleozoic limestones. See also: Cyanobacteria; Extinction (biology); Foraminiferida; Limestone
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