Test Morphology-SEPM strata

Paleontology > Foraminifera Introduction > Test Morphology

Test Morphology

Foraminifera come in a variety of shapes and sizes and can range in size from a few centimeters to microscopic. Their shell structures can be quite simple (open tubes or hollow spheres) or may be constructed of incredibly complex systems of chambers. Chambers are added during growth and the size of the test is associated with the amount of cytoplasm, therefore, as the organism feeds, the amount of cytoplasm increases, so the test must enlarge, or "grow". There are several types of growth patterns, resulting in a diverse variety of test morphology.

There are three main factors that modify the shape of the living cell. The first is the shape of the first chamber (proloculus) and the growth of the second chamber (deuteroloculus). These chambers are separated by a wall (septum) and connected by intercameral lumen. The second factor is the chamber shape and the third factor is the arrangement of chambers.

Chamber arrangement

The arrangement of the chambers may be annular concentric (two dimensions) or spherical-concentric (three dimensions).The chambers can be arranged in a serial arrangement, uniserial arrangement (chambers arranged in a single row), biserial arrangement (chambers arranged in two rows), etc. Alternatively, they may occur in a spiral arrangement, where coiling occurs in different planes, a planispiral arrangement where the spiral and umbilical sides are identical and symmetrical or the trochospiral arrangement where spiral and umbilical sides are dissimilar.

Aperture style

Larger foraminifera have many different overall adult shapes. As foraminifera increase in size, their internal structures become more complicated and as shells become larger, it is essential for the protoplasmic body of the unicellular cell to inhabit all compartments, therefore, a system of apertures (or stolons) is necessary to shorten the distance between the first and final chambers, and to provide a communication system between the compartments. This is provided by leaving a primary aperture for extrusion of the rhizopods between the chambers during growth and the linear nature of the rhizopodial protoplasm involved in wall building ensures that successive chambers are connected by a single aperture or foramen. In this way, the final chamber formed is open to the surrounding water (Hottinger, 1978; 2000).

** Page generated by Kerry McCarney-Castle; text summarized from BouDagher-Fadel (2008)**