Foraminifera
Allogromiida
Carterinida
Fusulinida - extinct
Globigerinida
Involutinida
Lagenida
Miliolida
Robertinida
Rotaliida
Silicolocunida
Spirillinida
Textulariida
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The
Foraminifera are a large group of
amoeboid protists with reticulating pseudopods, fine strands that branch and merge to form a dynamic net. They produce a shell, or test, which can have either one or multiple chambers, some becoming quite elaborate and beautiful in structure. Their tests are often made of calcium carbonate (calcareous), but can also be simply organic or even made up of small pieces of sediment cemented together (agglutinated). Foraminiferans are marine, and are very common in the
meiobenthos, although a few are
planktonic. Some are relatively large, a few reaching over 10 cm in diameter.
Tens of thousands of species are recognized, some living and some fossil, and they make up an important part of many marine sediments. Some are known as far back as the
Cambrian period. The form of the test is the primary means by which foraminferans are identified and classified. Nummulitic limestone, which makes up the pyramids of Egypt, is almost entirely ancient foraminifera.
A few other amoeboids produce reticulose pseudopods but lack elaborate tests, and these have been considered possible relatives of the foraminiferans, grouped together as the Granuloreticulosa. However, with the exception of
Reticulomyxa, shown by genetic studies to be a foraminiferan that has lost its shell, their affinities appear to lie elsewhere. Several are placed among the
Cercozoa, a diverse group closely related to the true foraminiferans. Both these groups are included among the
Rhizaria.
A number of foraminifera have developed
endosymbiotic interactions with unicellular
algae. Their endosymbionts span divergent lineages such as the
green algae,
red algae,
dinoflagellates,
chrysophytes, and
diatoms. Some sequester
chloroplasts of the algae they feed upon, and gain food from
photosynthesis in these stolen chloroplasts, a condition known as
