The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for Prymnesium), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at the class rank rather than as a division. Although the phylogenetics of this group has become much better understood in recent years, there remains some dispute over which rank is most appropriate.
Cell scheme. 1-haptonema
, 4-Golgi apparatus
, 6-scales, 7-chrysolaminarin vacuole
, 11-endoplasmic reticulum
, 12-chloroplast endoplasmic reticulum, 13-pyrenoid
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 red algal 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.
The best-known haptophytes are coccolithophores, which make up 673 of the 762 described haptophyte species, and 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, forming chalk deposits. 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.
Haptophytes are economically important, as species such as Pavlova lutheri and Isochrysis sp. are widely used in the aquaculture industry to feed oyster and shrimp larvae. They contain a large amount of polyunsaturated fatty acids such as docosahexaenoic acid (DHA), stearidonic acid and alpha-linolenic acid. Tisochrysis lutea contains betain lipids and phospholipids.
The haptophytes were first placed in the class Chrysophyceae (golden algae), but ultrastructural data have provided evidence to classify them separately. 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.
Haptophytes was discussed to be closely related to cryptomonads.
Haptophytes are closely related to the SAR clade.
Subphylum Haptophytina Cavalier-Smith 2015 [Haptophyta Hibberd 1976 sensu Ruggerio et al. 2015]
- Clade Rappemonada Kim et al. 2011
- Clade Haptomonada (Margulis & Schwartz 1998) [Haptophyta Hibberd 1976 emend. Edvardsen & Eikrem 2000; Prymnesiophyta Green & Jordan, 1994; Prymnesiomonada; Prymnesiida Hibberd 1976; Haptophyceae Christensen 1962 ex Silva 1980; Haptomonadida; Patelliferea Cavalier-Smith 1993]
- Class Pavlovophyceae Cavalier-Smith 1986 [Pavlovophycidae Cavalier-Smith 1986]
- Class Prymnesiophyceae Christensen 1962 emend. Cavalier-Smith 1996 [Haptophyceae s.s.; Prymnesiophycidae Cavalier-Smith 1986; Coccolithophyceae Casper 1972 ex Rothmaler 1951]
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