Their have been many variations of shell abnormalities of Benthic Foraminifera. Some of these abnormalities are: decrease in chamber size, aberrant chamber shape, distortion of the arrangement of chambers, abnormal protruding chambers, siamese twins and non developed tests.
Some of these abnormalities have been so severe that it is impossible to determine which part of the test was affected.
Note: Evidence of increase in heavy metal pollutants can also be caused by natural environmental stresses. (ie. extreme conditions)