Morphological abnormalities of foraminiferal tests have been studied in cultures of Ammonia tepida and A. beccarii. Regular asexual reproduction cycles of A. tepida show the influence of high salinity on the morphology of juveniles and on the ontogenetic process. A low rate of abnormalities (about 1%) occurs under normal saline conditions (37‰). These are mainly “double tests” or a protuberance on the spiral side, or an abnormal arrangement of the first several chambers. A high rate of abnormalities among the juvenile forms (about 50%) occurs under hypersaline conditions (50‰). These abnormalities include an abnormal shape of the proloculus or of the first several chambers, a modification of the coiling plane of the first several chambers, the development of two whorls from one proloculus, or the fusion of two juveniles. Some adults exposed to hypersaline conditions before the end of their growth have also shown a strong response that is manifested either in abnormal-sized chambers, or in numerous chambers with a complex arrangement. In paralic and coastal environments characterized either by salinity fluctuations or by hypersalinity, morphological abnormalities are similar to those seen in cultures, and can be explain by the same processes.
Other phenomena can cause abnormalities in the test. Asexual reproduction can lead to the construction of abnormal chambers on the umbilical side. Decalcification can result in the formation of small additional chambers or new chambers located between two septal walls of the decalcified initial chamber. Regeneration may occur after test damage; this feature is generally recognizable by the scars present on the test.
To have utility for various environmental applications we recommend using the term “deformations” to describe abnormalities formed by modification of the test during the life of the foraminifer, and the term “malformations” only to describe abnormalities resulting from an anomaly in the ontogenetic development process. When the origin of the abnormality is not evident, the words “morphological abnormalities” or “abnormal tests” can be used.