Coccolithophore

Coccolithophores (also called coccolithophorids) are single-celled algae, protists and phytoplankton belonging to the class haptophytes. They are distinguished by special calcium carbonate plates (or scales) of unknown purpose called coccoliths, which are important microfossils. Coccolithophores are exclusively marine and are found in large numbers throughout the surface euphotic zone of the ocean. An example of a globally-significant coccolithophore is Emiliania huxleyi.

Due to their microscopic size and the broad distribution of many of their taxa, coccoliths (calcareous nannoplankton) have become very popular as index fossils for solving various stratigraphic problems. Nannofossils are sensitive indicators of changes in the temperature and salinity of the ocean and sea surface water. The quantitative analysis of calcareous nannoplankton assemblages is being employed to reveal such changes.