Thehaptophytes, classified either as theHaptophyta,Haptophytina orPrymnesiophyta (named forPrymnesium), are aclade ofalgae.
The namesHaptophyceae orPrymnesiophyceae are sometimes used instead.[2][3][4] This ending implies classification at theclassrank rather than as a division. Although thephylogenetics of this group has become much better understood in recent years, there remains some dispute over which rank is most appropriate.
Thechloroplasts are pigmented similarly to those of theheterokonts,[5] 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 similarred algal endosymbionts. Haptophyte chloroplasts contain chlorophyllsa,c1, andc2 but lack chlorophyllb. For carotenoids, they havebeta-,alpha-, andgamma- carotenes. Likediatoms andbrown algae, they have alsofucoxanthin, an oxidized isoprenoid derivative that is likely the most important driver of their brownish-yellow color.[6]
The cells typically have two slightly unequalflagella, both of which are smooth, and a unique organelle called ahaptonema, which is superficially similar to a flagellum but differs in the arrangement ofmicrotubules and in its use. The name comes from theGreekhapsis, touch, andnema, round thread. Themitochondria have tubularcristae.
Most haptophytes reportedly producechrysolaminarin rather thanstarch as their major storage polysaccharide, but somePavlovaceae produceparamylon.[7][8] The chain length of the chrysolaminarin is reportedly short (polymers of 20–50 glycosides, unlike the 300+ of comparableamylose), and it is located in cytoplasmic membrane-bound vacuoles.[8]
The best-known haptophytes arecoccolithophores, which make up 673 of the 762 described haptophyte species,[9] and have an exoskeleton of calcareous plates calledcoccoliths. Coccolithophores are some of the most abundant marinephytoplankton, especially in the open ocean, and are extremely abundant as microfossils, formingchalk deposits. Other planktonic haptophytes of note includeChrysochromulina andPrymnesium, which periodically form toxic marinealgal blooms, andPhaeocystis, blooms of which can produce unpleasant foam which often accumulates on beaches.[10]
The haptophytes were first placed in the classChrysophyceae (golden algae), but ultrastructural data have provided evidence to classify them separately.[13] 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.[10]
Haptophytes was discussed to be closely related tocryptomonads.[14]
Haptophytes are closely related to theSAR clade.[15]
Subphylum HaptophytinaCavalier-Smith 2015 [HaptophytaHibberd 1976 sensu Ruggerio et al. 2015][16]
^Andersen RA (October 2004). "Biology and systematics of heterokont and haptophyte algae".American Journal of Botany.91 (10):1508–22.doi:10.3732/ajb.91.10.1508.PMID21652306.
^Tsuji, Yoshinori; Yoshida, Masaki (2017). "Biology of Haptophytes: Complicated Cellular Processes Driving the Global Carbon Cycle".Advances in Botanical Research. Vol. 84. Elsevier. p. 219–261.doi:10.1016/bs.abr.2017.07.002.ISBN978-0-12-802651-9.
^Renaud SM, Zhou HC, Parry DL, Thinh LV, Woo KC (1995). "Effect of temperature on the growth, total lipid content and fatty acid composition of recently isolated tropical microalgae Isochrysis sp., Nitzschia closterium, Nitzschia paleacea, and commercial species Isochrysis sp. (clone T.ISO)".Journal of Applied Phycology.7 (6):595–602.doi:10.1007/BF00003948.S2CID206766536.
^Kato M, Sakai M, Adachi K, Ikemoto H, Sano H (1996). "Distribution of betaine lipids in marine algae".Phytochemistry.42 (5):1341–5.doi:10.1016/0031-9422(96)00115-X.
^Reeb VC, Peglar MT, Yoon HS, Bai JR, Wu M, Shiu P, et al. (October 2009). "Interrelationships of chromalveolates within a broadly sampled tree of photosynthetic protists".Molecular Phylogenetics and Evolution.53 (1):202–11.doi:10.1016/j.ympev.2009.04.012.PMID19398025.
