The
haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a group of
algae. The
chloroplasts are pigmented similarly to those of the
stramenopiles, 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 behavior. The most important group of haptophytes are the
coccolithophores.