Haptophyte

Haptophytes
Coccolithophore (Coccolithus pelagicus)
Scientific classification
Domain:	Eukaryota
Kingdom:	Chromalveolata
Division:	Haptophyta Hibberd 1972 ex Edvardsen & Eikrem in Edvardsen et al. 2000
Classes & Orders
Class Pavlovophyceae Pavlovales Class Prymnesiophyceae s.s. (= Haptophyceae s.s.) Prymnesiales Phaeocystales Isochrysidales Coccolithales
Synonyms
Prymnesiophyta Green & Jordan, 1994 Prymnesiophyceae s.l. Casper, 1972, ex Hibberd, 1976 Haptophyceae s.l. Christensen, 1962 ex Silva, 1980

The haptophytes, classified either as the Prymnesiophyta (named for Prymnesium) or Haptophyta, are a division 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.

Characteristics

Cell scheme. 1-haptonema, 2-flagella, 3-mitochondrion, 4-Golgi apparatus, 5-nucleus, 6-scales, 7-crysolaminaran vacuole, 8-plastid, 9-ribosomes, 10-stigma, 11-endoplasmic reticulum, 12-chloroplast endoplasmic reticulum, 13-pyrenoid, 14-thylakoids.

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.

Economic importance

Haptophytes are economically important as Pavlova lutheri and Isochrysis sp. are widely used in the aquaculture industries.

Examples and classification

Further information: Wikispecies:Haptophyta

The haptophytes were first placed in the class Chrysophyceae (golden algae) but ultrastructural data have provided evidence to classify them separately. 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

Haptophytes was discussed to be closely related to cryptomonads.

Haptophytes are closely related to the SAR clade.