microscopic single-celled marine algae (phytoplankton) which secrete carbonate plates known as coccoliths.

a unicellular planktonic organism of uncertain type (protozoan or algae?). Currently assigned the phylum Haptomonada.

Coccolithophores are single-celled algae, or phytoplankton, belonging to the 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.