Pleistocene and other Diatom Earths.—Card, G. W. and Dun, W. S., Rec. Geol. Surv. New South Wales, vol. V. pt. 3, 1897, p. 128.
[CHAPTER VI.]
FOSSIL FORAMINIFERA AND RADIOLARIA.
Protozoans, Their Structure.—
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The animals forming the sub-kingdom PROTOZOA (“lowliest animals”), are unicellular (one-celled), as distinguished from all the succeeding higher groups, which are known as the METAZOA (“animals beyond”). The former group, Protozoa, have all their functions performed by means of a simple cell, any additions to the cell-unit merely forming a repetitional or aggregated cell-structure. A familiar example of such occurs in pond-life, in the Amoeba, a form which is not found fossilised on account of the absence of any hard parts or covering capable of preservation. Foraminifera and Radiolaria, however, have such hard parts, and are frequently found fossilised.
Foraminifera: Their Habitats.—
The FORAMINIFERA are a group which, although essentially one-celled, have the protoplasmic body often numerously segmented. The shell or test formed upon, and enclosing the jelly-like sarcode, may consist either of carbonate of lime, cemented sand-grains, or a sub-calcareous or chitinous (horny) covering. The Foraminifera, with very few exceptions, as Mikrogromia, Lieberkuehnia, and some forms of Gromia, are all marine in habit. Some genera, however, as Miliolina, Rotalia and Nonionina, affect brackish water conditions.