Origin of morphological abnormalities in Ammonia (Foraminifera): Studies in laboratory and natural environments

Morphological abnormalities of foraminiferal tests have been studied in cul tures of Ammonia tepida and A. beccarri. Regular asexual reproduction cycle s of A. tepida show the influence of high salinity on the morphology of juv eniles and on the ontogenetic process. A low rate of abnormalities (about 1 %) occurs under normal saline conditions (37%). These are mainly "double te sts" or a protuberance on the spiral side, or an abnormal arrangement of th e first several chambers. A high rate of abnormalities among the juvenile f orms (about 50%) occurs under hypersaline conditions (50%). These abnormali ties include an abnormal shape of the proloculus or of the first several ch ambers, a modification of the coiling plane of the first several chambers, the development of two whorls from one proloculus, or the fusion of two juv eniles. Some adults exposed to hypersaline conditions before the end of the ir growth have also shown a strong response that is manifested either in ab normal-sized chambers, or in numerous chambers with a complex arrangement. In paralic and coastal environments characterized either by salinity fluctu ations or by hypersalinity, morphological abnormalities are similar to thos e seen in cultures, and can be explain by the same processes. Other phenomena can cause abnormalities in the test. Asexual reproduction c an lead to the construction of abnormal chambers on the umbilical side. Dec alcification can result in the formation of small additional chambers or ne w chambers located between two septal walls of the decalcified initial cham ber. Regeneration may occur after test damage; this feature is generally re cognizable by the scars present on the test. To have utility for various environmental applications we recommend using t he term "deformations" to describe abnormalities formed by modification of the test during the life of the foraminifer, and the term "malformations" o nly 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.