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  • Characteristic genus: Euglena

  • Abundant in almost any nutrient-rich freshwater system
  • Dissolved organic material fosters euglenophyte abundance
  • Require vitamins B1 and B12 – auxotrophic species
  • Pigments: Chl.a, Chl.b, b-carotene, diadinoxanthin
  • Secondary plastids; some species possess colorless plastids or lost their plastids; these species are phagotrophic
  • Color of most species green, but some produce red water blooms

  • One or two (visible) flagella of typical eukaryotic 9+2 structure

  • Evolutionary probably the oldest group of eukaryotic algae
  • Unicellular motile or sessile forms
Cell Structure
  • Flagella: 2 flagella emerge from a pocket at the cell anterior (reservoir, ampulla); sometimes only 1 flagellum extends outside the pocket; flagella carry one row of long hairs and shorter hairs on flagella surface

  • Phototrophic species possess an eye-spot made of carotenoids (directed swimming to light source = phototaxis)
  • Secondary plastids show 3 membrane layers

  • Storage product: paramylon, does not stain blue-black with iodine

  • Euglenophyte Flagellar Apparatus
    • Ampulla evolved from separate flagella and the cytostome („cell mouth“)
    • Contractile vacuole: adjacent to ampulla; discharges excess water into ampulla
    • Paraflagellar rod: protein structure at the roots of flagella, makes flagella appear thicker, involved in flagella motion control
    • Flagellar roots: bands of microtubules from flagella bases to cytoplasm, act like muscles (control cell shape); striated connective between flagella bases coordinates flagellar motion

Euglenophyte Swimming

  • Swim by one or two flagella; only the tip of flagellum is moving, propelling the cell forward

  • see the heterotrophic euglenophyte Peranema swim (QuickTime 960 kB)
  • Light sensing system: 2 major parts, 
    • paraflagellar rod at the base of at least the emergant flagellum; contains light-sensitive flavins
    • Eye-spot (stigma): in the cytoplasm adjacent to the ampulla; bright orange by carotenoids
    • Light direction: the eye-spot shades the paraflagellar body while cell is swimming in rotating movements along its axis
  • Positive phototaxis: most photo- trophic euglenophytes swimm towards the light source

Pellicle and Metaboly
  • Cell wall is called pellicle, made 70-80% protein plus lipids
  • Pellicle is organized in strips, long ribbons that extend helically along the cell; the edges of the ribbons are bent upwards and downwards, resp.

    Upper: schematic drawing of the euglenophyte pellicle, showing four strips with their bent edges and rows of four microtubuli; middle: cross section (EM) through the pellicle (left) and a Euglena cell (right); lower: scanning electron micrographs of the pellicle of Euglena (left) and Phacus (right).

  • Microtubuli at the edge of the stripes faciliate lateral sliding of strips past each other
  • Metaboly: flexible movement of the pellicle cause change of cell shape; typical for euglenophytes only; allows to stem through sand grains, etc.
    See also mataboly QuckTime (1.3 MB)
  • Cell division: prior to cell division, pellicle strips are doubled
  • Mucilage: euglenophytes can excrete polysaccharids or glycoproteins from mucocysts. Mobile cells have only thin mucilage layer, but immobile, round cells can aggregate in thick jelly layers: palmella or palmelloid stages

Euglenophyte cysts (left); stained mucocysts in Euglena (right)


  • Asexual reproduction by longitudinal cell division starting from the front end of the cell
  • DNA is permanently condensed, i.e. no cell cycle changes in coiling
  • Mitosis: nucleus moves towards the ampulla/reservoir; mitosis occurs within nucleus envelope
  • Sexual reproduction: unknown
  • Cysts are formed to survive unfavorable conditions; thick, mucilaginous cell wall, loss of flagella, eye-spot mostly present, rounding of cells, increase in paramylon granules

    Germinating cysts of the heterotrophic, colorless Pernanema

See also a QuickTime movie on the feeding of Entosiphon, using its funnel-shaped feeding apparatus (1.46 MB)