The final major test composition found in foraminifera is a proteinaceous mucopolysaccharide organic wall. This wall provides a fairly strong and elastic test similar to the exoskeletons of the mesoscopic insects. Most foraminifera have such a wall that forms the basis for either agglutination of particles or serves as a base over which a secreted test can be grown.
These last few pages have covered most of the basic test compositions that can be found in foraminifera. There are of course exceptional cases of secreted tests that have been documented and may be worth noting. Spirillinina Patellina was recognized to have its entire test grown from one optically single calcite crystal. Aragonite tests are another anomaly as far as secreted tests go. The genus Carterina is thought to be composed of spicules of either secreted or agglutinated calcite.
It was found that if one plotted shell-type ratios, general correlations could be made with respect to the particular modern environment from which the samples were taken. This is demonstrated in the accompanying triangular plot (click on it to see enlargement). This of course has proven to be an exceptional paleoenvironmental indicator for fossilized foraminifera.
The foraminiferan test is the only preservable morphology that can be found fossilized within the rock record or even within recent sediments for that matter. There are varying morphologies that can be observed directly only through living specimens, which can be difficult due to the microscopic size of these creatures. Click on home to procede and find out more about the living foraminifera.