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.References
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