Revisiting the Nomenclature of Haptophytes

The coccolithophorids are a well-established group of unicellular algae whose bodies are covered by calcareous scales. They are usually assigned to the class Haptophyceae or Prymnesiophyceae, but we present arguments in favor of the name Coccolithophyceae. The taxonomic diversity within the coccolithophorids far exceeds that within the remaining members of the class. Molecular evidence shows phylogenetic closeness of coccolithophorids to certain haptophytes that do not form coccoliths, suggesting that the ability to produce calcareous scales has arisen only once and has been lost in some haptophytes. Electron microscopical detection of weak calcification in noncoccolithophorid haptophytes further supports the view that calcification is distributed throughout the class. Of three available names for the class, Coccolithophyceae Rothmaler 1951 has priority over Prymnesiophyceae Casper ex Hibberd 1976 and Haptophyceae Christensen ex P.C. Silva 1980. We urge the use of the name Coccolithophyceae for t...