The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a group of algae. The chloroplasts are pigmented similarly to those of the heterokonts, such as golden algae, but the structure of the rest of the cell is different, so it may be that they are a separate line whose chloroplasts are derived from similar endosymbionts.
The cells typically have two slightly unequal flagella, both of which are smooth, and a unique organelle called a haptonema, which is superficially similar to a flagellum but differs in the arrangement of microtubules and in its use. The name comes from the Greek hapsis, touch, and nema, thread.
The most important group of haptophytes are the coccolithophores, which are ornamented with calcite scales called coccoliths that may form microfossils. Two genera of haptophytes, Chrysochromulina and Prymnesium , periodically form toxic marine algal blooms.