Prymnesiophyceae (Haptophyceae) A class of predominantly unicellular, flagellated algae (sometimes regarded as protozoa, class Phytomastigophora) in which there are two smooth (whiplash-type) flagella, and a structure called a haptonema: a filamentous appendage which may be short, or long and whip-like, and which is believed to function mainly in attaching the organism to a solid surface. Species are predominantly marine, often forming a major component of the phytoplankton in some regions. Many species have a cell covering of many small scales; in some species these scales are impregnated with calcium carbonate and are known as coccoliths.

Haptophyceae See PRYMNESIOPHYCEAE.