The foram cell typically occupies all but the one or two most recently added chambers, the last of which opens out to the seawater. In their simplest forms, tests may be little more than hollow balls or open tubes. But some foram tests can take very complex shapes. Depending on the species, foram tests may be made of sand grains, organic compounds, and other particles cemented together, or they may be made of crystalline calcite, the same mineral that sea shells are made of. Calcarina sliced open like an apple cut in half.
Large holes are where algae live.
The chambers in larger foram tests often serve as a home for algae and cyanobacteria as well. Forams also eat bacteria, diatoms, other protozoa and even small animals such as copepods. In turn, forams are an important food source for snails, sand dollars, fish and other creatures. Some species are single-celled creatures that can't be seen without a microscope. Yeast is an example.