Foraminifera

Foraminifera, or forams, are single-celled amoeboid protists. Their principal characteristics are:

1. Threadlike anastomosing pseudopodia bearing granules that reveal constant bidirectional streaming of the cytoplasm.

2. The life history characterized by an alteration of sexual and asexual generations with meiosis associated with the asexual reproduction - a feature unique in heterotrophic eukaryotes; and

3. The presence of a test (shell). This can have either one or multiple chambers, some becoming quite elaborate in structure.

About 275,000 species are recognized, both living and fossils. Forams are abundant all over the ocean. They either live on the sea bottom (benthic) or float in the upper water column (planktonic). Of the estimated 4000 species living today, 40 are planktonic. This count may however represent only a fraction of actual diversity, since many genetically discrepant species may be morphologically indistinguishable. A few benthic species have been recorded from terrestrial environments including ground water.

The size of the foraminiferal test (shell) typically ranges from 0.05mm to 0.5mm although some forams may be as large as several centimeters with a recorded maximum of 18cm in diameter. Foraminifera remain single-celled despite the large sizes they reach. The cell is divided into granular endoplasm and transparent ectoplasm. The pseudopodial net may emerge through a single opening or many perforations in the test, and characteristically has small granules streaming in both directions. The pseudopods are used for locomotion, anchoring, and in capturing food, which consists of small organisms such as diatoms or bacteria.

Foraminifera are among the most abundant shelled organisms in many marine environments. A cubic centimeter of sediment may hold hundreds of living individuals, and many more dead shells. In some environments their shells are an important component of the sediment.

The study of fossil foraminifera has many applications beyond expanding our knowledge of the diversity of life. Fossil foraminifera are useful in biostratigraphy, paleoecology, paleobiogeography, and oil exploration.

What I have said here is a very short and simplistic description of these fascinating organisms that have such a story to tell about the earth’s history and ecology. For a more detailed and interesting description the website of the University College of London Micropalaeontology Unit should be visited.