Thin microtubule-based appendages (haptonema or axopodia) used for feeding; complex mineralized (siliceous or calcareous) scales. Two major groups.
Haptophyta: Autotrophic or heterotrophic flagellates have 2 (rarely 4) smooth or rough unequal flagella at their anterior end. Between the flagella there is a filamentous structure – the haptonema which serves to attach to the substrate, move and capture food. In contrast to the flagellar axoneme, a transverse section of the haptoneme shows a bundle of 6–8 microtubules surrounded by cisterns of endoplasmic reticulum. Plastids containing chlorophylls a and c, as well as fucoxanthin, are covered with a membrane of the endoplasmic reticulum. Mitochondria with tubular cristae. Cells naked or covered with organic scales (Prymnesium – freshwater unicellular algae), in some marine forms with large calcareous scales of complex structure (Coccolithus – marine unicellular algae). The life cycle alternates between stationary and motile stages. The sexual process is not known.
Centrohelids: Heterotrophic unicellular amoeboid organisms with long radially arranged axopodia diverging from a single center, the axoplast. The pellicular cover with trichocysts and scale deposits of various shapes and compositions. Mitochondria having flat cristae. Predominantly freshwater planktonic forms. The sexual process is not known.
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Cavalier-Smith T., von der Heyden S. Molecular phylogeny, scale evolution and taxonomy of centrohelid Heliozoa. Molec. Phylog. Evol. 2007. V. 44 (3). P. 1186–1203. https://doi.org/10.1016/j.ympev.2007.04.019

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Edvardsen B., Eikrem W., Green J.C. et al. Phylogenetic reconstructions of the Haptophyta inferred from 18S ribosomal DNA sequences and available morphological data. Phycologia. 2000. V. 39. P. 19–35.

Febvre-Chevalier C., Febvre J. Axonemal microtubule pattern of Cienkowskya mereschkovskyi and a revision of heliozoan taxonomy. Origins of Life and Evolution of Biospheres. 1984. V. 13 (3). P. 315–338. https://doi.org/10.1007/BF00927180

Shishkin Y., Drachko D., Klimov V.I. et al. Yogsothoth knorrus gen. n., sp. n. and Y. carteri sp.n. (Yogsothothidae fam. n., Haptista, Centroplasthelida), with notes on evolution and systematics of centrohelids. Protist. 2018. V. 169. P. 682–696. https://doi.org/10.1016/j.protis.2018.06.003
• DIAPHORETICKES [Adl et al., 2012]
•• Haptista [Cavalier-Smith, 2003]
••• Haptophyta [Hibberd, 1976]
•••• Pavlovaphyceae [Edvardsen et al., 2000]
•••• Prymnesiophyceae [Hibberd, 1976]
••• Centroplasthelida [Febvre-Chevalier, Febvre 1984]
•••• Pterocystida [Cavalier-Smith, von der Heyden 2007]
•••• Panacanthocystida [Shishkin et al., 2018].

Rank correlation:
• ~Subdomain
•• ~ Kingdom
••• ~ Phylum
••••~ Class