20 November 2006

A shell of a different kind

Empty shells of land snails usually accumulate soil and all sorts of debris in them, especially if they have wide apertures. One can dislodge most of what is inside the bodywhorl of a shell by squirting water inside, by gently tapping on the shell or by inserting something long and curved with a blunt tip deep into the shell. Often, the soil that comes out of a large shell will have tiny snail shells in it. Therefore, it is a good idea to sort thru that soil before discarding it away.

Yesterday afternoon I examined some land snail shells (in the family Hygromiidae, to be specific) that had been collected near a beach. A small amount of beach sand came out of the shells, which I collected in a small dish. And before tossing it away, I scanned it under the stereomicroscope. Among the tiny sand grains was this tiny foraminiferan shell almost exactly a millimeter wide.


Foraminifera, called forams by those who study them, are mostly microscopic and exclusively marine organisms in the kingdom Protista.

In the 1950s, the Foraminifera, along with other microscopic organisms ("protozoa"), were considered to be animals. For that reason, there is a chapter about them in Invertebrate Fossils by Moore et al1. Many foraminiferan shells (tests) look quite like snail shells. And like snail shells, most foraminiferan shells are also made of CaCO3.

Some forams with snail-like shells. Drawings from Moore et al1.

1. Moore, Lalicker & Fischer. 1952. Invertebrate Fossils. McGraw Hill.



Harry G. Lee e-mailed the following comments:

Although most forams with coiled shells are planospiral like the two in Aydin's sample illustrations, many have a helical (called trochospiral by specialists) form, like Ceratobulimina, the illustration in the center of the composite. In gastropod parlance the topology of its coil (chirality) is dextral. Some forams make shells which are characteristically sinistral, and the chirality has a phylogenetic basis. Forams have been around for over half a billion years, and over geological time some taxa underwent one or more reversal in chirality. These relatively instantaneous evolutionary events were followed by varying, often relatively short, periods of morphological stasis. Thus these microfossils may be used as fairly precise chronostratigraphic indicators. The presence or absence of fossil fuel is intimately wed to the same paleontological clock, and is often limited to rather narrow layers in the stratigraphic column. Petroleum geologists, applying their (or others') micropaleontology, exploited close correlations between the occurrence of trochospiral forams, often diagnosed principally on their chirality, and fuel in the fossil record as an invaluable technique in oil prospecting. In other words the coil of a certain foram in the stratum meant the difference between a dry well and a gusher.

Nowadays, seismology has largely supplanted paleontology as a means to find fossil fuel deposits, and the latter discipline has sustained a depletion in its ranks along with an aging of its cohort. Sadly, this is an illustration of the economic (and social) impacts felt in the "applied sciences." Paradoxically, much of the "basic science" of what we know today of fossil Foraminifera was written by paleontologists in the employ of major oil corporations - not in residing in purely academic or museum settings.

Anonymous said...

I am almost sure that it is a baby woodlouse. See the the segments are ridged platelets. You will see if you open the "shell" the minute legs hidden inside the animal. They (Ligidae) can live by sea and lakes.



I am almost sure you need new glasses, Ümit.

MassBile said...
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