The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a phylum of algae.
The term "Haptophyceae" is sometimes used. This ending implies classification at a lower level. However, although the phylogenetics of this group has become much more understood in recent years, there remains some dispute over which taxon level is most appropriate.
The chloroplasts are pigmented similarly to those of the heterokonts, 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 mitochondria have tubular cristae.
Haptophytes are economically important as Pavlova lutheri and Isochrysis sp. are widely used in the aquaculture industries.
Examples and classification
The best-known haptophytes are coccolithophores, which have an exoskeleton of calcareous plates called coccoliths. Coccolithophores are some of the most abundant marine phytoplankton, especially in the open ocean and are extremely abundant as microfossils. Other planktonic haptophytes of note include Chrysochromulina and Prymnesium, which periodically form toxic marine algal blooms, and Phaeocystis blooms of which can produce unpleasant foam which often accumulates on beaches. Both molecular and morphological evidence supports their division into five orders; coccolithophores make up the Isochrysidales and Coccolithales. Very small (2-3μm) uncultured pico-prymnesiophytes are ecologically important
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