The living coccolithophores are marine, unicellular, flagellate phytoplankton, belonging to the phylum Haptophyta and division Prymnesiophyceae. Haptophyte algae have golden-brown chloroplasts, an exoskeleton of scales and a unique flagella-like structure, known as the haptonema. Within the Haptophyta, only the coccolithophores produce calcified scales know as coccoliths. Coccolithophores produce two types of disc-like coccoliths, heterococcoliths and holococcoliths, which are distinguished by their morphology, mode of formation, and life-cycle stage during which they are produced. They can also produce non-coccolith structures, such as ceratoliths (e.g. Ceratolithus) and pentaliths (e.g. Braarudosphaera), which diverge from the typical disc-like form. Many extinct non-coccolith (nannolith) fossils may also have been produced by coccolithophores.
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