So important is the test to the biology of foraminifera that it provides the scientific name of the group—foraminifera, Latin for "hole bearers", referring to the pores connecting chambers of the shell in the multi-chambered species.

[8] The hard nature of most foraminiferal tests leads to an excellent fossil record, and they are widely researched to infer information about past climate and environments.

Owing to their generally hard and durable construction (compared to other protists), the tests of foraminifera are a major source of scientific knowledge about the group.

Test shape is highly variable among different foraminifera; they may be single-chambered (unilocular) or multi-chambered (multilocular).

A wide variety of test morphologies is found in both unilocular and multilocular forms, including spiraled, serial, and milioline, among others.

Tests as fossils are known from as far back as the Ediacaran period,[12] and many marine sediments are composed primarily of them.

[14] Genetic studies have identified the naked amoeba Reticulomyxa and the peculiar xenophyophores as foraminiferans without tests.

A few other amoeboids produce reticulose pseudopodia, and were formerly classified with the forams as the Granuloreticulosa, but this is no longer considered a natural group, and most are now placed among the Cercozoa.

[18] Other forams have tests made from small pieces of sediment cemented together (agglutinated) by either proteins (possibly collagen-related), calcium carbonate, or Iron (III) oxide.

However, recent genetic studies suggest that "astrorhizids" do not make up a natural grouping, instead forming a broad base of the foram tree.

This calcite cement is made up of small (<100 nm) globular nanograins, similar to in other globothalameans.

It is thought to use the spicules as both a means of elevating itself off the seabed as well as to lengthen the reach of its pseudopodia to capture prey.

Xenophyophores selectively uptake sediment grains between 63 and 500 μm, avoiding larger pebbles and finer silts; type of sediment seems to be a strong factor in which particles are agglutinated, as particle type preferentially includes sulfides, oxides, volcanic glass, and especially tests of smaller foraminifera.

Some supposed "monocrystalline" spirillinids have been found to actually have tests consisting of a mosaic of very small crystals when observed with scanning electron microscope.

[20] Lagenid tests consist of "fibre bundles" that can reach tens of micrometres long; each "bundle" is formed from a single calcite crystal, is triangular in cross-section, and has a pore in the centre (thought to be an artefact of test deposition).

They are formed from low-to-high-magnesium calcite "nanograins" positioned with their C-axes perpendicular to the external surface of the test.

The now-extinct Fusulinids have traditionally been considered unique in having tests of homogenous microgranular crystals with no preferred orientation and almost no cement.

[24] The Carterinids, including the genera Carterina and Zaninettia, have a unique crystalline structure of the test which long complicated their classification.

However, life studies have failed to find agglutination, and in fact the genus has been discovered on artificial substrate where sediment particles do not accumulate.

[27] A 2014 genetic study found carterinids to be an independent lineage within the Globothalamea, and supported the idea of the spicules being secreted as spicule shape differed consistently between specimens of Carterina and Zaninettia collected from the same locality (ovoid in Carterina, rounded-rectangular in Zaninettia).

The middle subunit is approximately 18μm in thickness and consists of a three-dimensional lattice of silica rods with no organic component in the open space.