Smallest Shells

The smallest shells are made by single-celled organisms!
One-celled amoebas called Arcellaceans create shells for themselves by glueing together bits of sand or other debris. Their discarded shells, also known as “tests”, become part of the sediment layer at the bottom of the freshwater lake or stream in which they lived, and they can fossilize.
Arcellacean tests come in a great variety of shapes, and their forms are very sensitive to the exact environment in which the amoebas live.
Scientists studying the sediments can use the form and quantities of tests to determine the conditions in ponds, lakes, or streams during the time when the sediments were laid down. This is helpful not only to understand prehistoric conditions, but also to know how more recent life forms respond to pollution.

Click here to see pictures of arcellacean tests and to learn more about Arcellaceans.

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