Foraminifera

Foraminifera

[You can click on the small pictures to view a larger version]

Foraminifera or foraminifers or forams (for short) generally very common in marine post-Palaeozoic rocks. They are quite easy to get out of soft rocks such as clays and marls, but can also be found in loose oolites, shell sands and chalks.

They are some of he simplest organisms in the animal kingdom, but they create some of the most beautiful and complicated shells.

Forams (the animals) are similar to amoebas but they tend to create a protective home to live in. These shells (or TESTS to use the correct term, can be quite simple or very complex.

Some will create a test of organic tectin material (which tend not to become fossilised), others attach grains of sediment to that organic test, and others (the majority of the fossilised forms) secrete a test of Calcium Carbonate, which might consist of a single chamber, or may have hundreds in a complicated arrangement.

From a practical point of view, forams can be divided into four main categories: the agglutinated forms (agluts for short), the benthic calcareous forams, the planktonic calcareous forams and large benthic foraminifera.

The Agglutinated Foraminifera build their test from grains of sediment. The grains could be quite small, giving it a smooth appearance, or larger with the individual grains being visible under the low power binocular microscopes we use to study them. The test can have just one chamber or many chambers arranged in different patterns.

The Calcareous Benthics have one or more chambers, and live in the sediment at the bottom of the sea, on the surface of the sediment, on plants or rocks, or attached to plants, rocks or other creatures. One group of benthic forams have shiny porcelaneous tests.

The Planktonic forams float in the sea. They are multi-chambered and tend to have quite lightweight delicate tests. Some develop keels around their edges to weigh them down a bit so they can maintain their position (depth) in the water column.

Large Benthic Forams live at the bottom of the sea. They are multi-chambered - very much so, but not very exciting to look at from the outside. They can be up to 15 cm in diameter, and are best studied by opening them up and viewing the internal arrangement of the chambers. They do have the advantage that you can see them with the naked eye and you can photograph them!