Coccoliths are the individual plates formed by coccolithophores such as Emiliana Huxleyi1, and arranged around them in a coccosphere. The coccoliths are shed continually during the coccolith's lifetime, as well as following the breakup of the coccosphere on death. They sink through the water column to form an important part of the sediments (depending on the water depth), where they were first identified by Thomas Huxley.
Although coccoliths are energetically expensive to produce, their purpose is unclear. Hypotheseses include defence against grazing by zooplankton or infection by parasites; maintenance of buoyancy; release of carbon dioxide for photosynthesis; and to filter out harmful UV light 2.
Coccoliths are composed of calcium carbonate as the mineral calcite and are the main constituent of chalk deposits such as the white cliffs of Dover.
