Foraminifera

Allogromiida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Carterinida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Fusulinida - extinct

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Globigerinida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Involutinida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Lagenida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Miliolida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Robertinida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Rotaliida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Silicolocunida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Spirillinida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Textulariida

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

incertae sedis

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

   Xenophyophorea

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

   Reticulomyxa

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands that branch and merge to form a dynamic net. They typically produce a shell, or test, which can have either one or multiple chambers, some becoming quite elaborate in structure. About 250 000 species are recognized, both living and fossil. They are usually less than 1 mm in size, but some are much larger, and the largest recorded specimen reached 19 cm.

Related Topics:
Amoeboid - Fossil - Largest

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Modern forams are exclusively marine, although they can survive in brackish conditions, and are very common meiobenthos, although a few are planktonic. The cell is divided into granular endoplasm and transparent ectoplasm. The pseudopodial net may emerge through a single opening opening or many perforations in the test, and characteristically has small granules streaming in both directions.

Related Topics:
Meiobenthos - Plankton

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The pseudopods are used for locomotion, anchoring, and in capturing food, which consists of small organisms such as diatoms. A number of forms have unicellular algae as endosymbionts, from diverse lineages such as the green algae, red algae, golden algae, diatoms, and dinoflagellates. Some forams are kleptoplastic, retaining chloroplasts from ingested algae to conduct photosynthesis.

Related Topics:
Diatom - Alga - Endosymbiont - Green alga - Red alga - Golden alga - Dinoflagellate - Kleptoplastic - Chloroplast - Photosynthesis

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The foraminiferan life-cycle involves an alternation between haploid and diploid generations, although they are mostly similar in form. The haploid or gamont initially has a single nucleus, and divides to produce numerous gametes, which typically have two flagella. The diploid or schizont is multinucleate, and after meiosis fragments to produce new gamonts. Asexual reproduction also occurs.

Related Topics:
Haploid - Diploid - Nucleus - Flagella - Meiosis

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The test is usually made of calcium carbonate (calcareous), but it can also be composed of organic material or made of small pieces of sediment cemented together (agglutinated). The form of the test is the primary means by which forams are identified and classified. Fossils are known from as far back as the Cambrian period, although the group did not begin to radiate extensively until the Carboniferous, and are commonly used in biostratigraphy.

Related Topics:
Calcium carbonate - Cambrian - Carboniferous - Biostratigraphy

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Many marine sediments are composed primarily of foraminiferan tests. For instance, the nummulitic limestone that makes up the pyramids of Egypt is composed almost entirely of them. Forams may also make a significant contribution to the overall deposition of calcium carbonate in coral reefs.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Genetic studies have identified the naked amoeba Reticulomyxa and the peculiar xenophyophores as foraminiferans without tests. A few other ameoboids produce reticulose pseudopods, 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. Both the Cercozoa and Radiolaria are close relatives of the Foraminifera, together making up the Rhizaria, but the exact position of the forams is still unclear.

Related Topics:
Xenophyophore - Cercozoa - Radiolaria - Rhizaria

~ ~ ~ ~ ~ ~ ~ ~ ~ ~