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  • Named after genus Synura
  • Silica-scaled flagellates, separated from chrysophyceans by their lack of chl.c2 and different flagellar root
  • Autotrophic, lost ability of phagotrophy
  • Occurrence predominantly oligotrophic freshwater
  • Flagella and flagellar roots are parallel (instead of perpendicular in chrysophyceans), both held in front of cell
  • Flagellar transformation: the flagella of a given cell are of different age; only one of the two flagella originates from the mother cell, the other flagellum is formed after cell division by the daughter cell
  • Scales are perforated and may carry perforated spines; produced in silica deposition vesicles and extruded outside cell membrane; bristles are formed in separate SDV
  • Silica depletion results in lack of scales but naked cells continue to grow

  • External silicon sceleton is present in at least one life-cycle stage
  • Few living species but extensive fossile records
  • Key genus: Dictyocha

  • Silica was thought to be necessary for growth
  • Kiel Bight, Western Baltic: A new phytoplankton bloom annual blooms discolored the water brown in May, which normally happened to be the „clearwater phase“; nutrient balance of nitrate:silicate was altered by eutrophication; Dictyocha speculum adapted to the new conditions in growing without its typical silica sceleton 
  • Characteristic genus: Pedinella
  • Unicellular flagellates with anterior ring of microtubuli-supported rhizopodia
  • Radial symmetry around longitudinal axis is exceptional among algae
  • Unmineralized, organic scales on cell surface
  • Plastids: 3-6 golden-brown plastids around the cell, containing chl. a,c, fucoxanthin; heterotrophic species lack plastids
  • Occurrence predominantely marine

Trybophyceans (Xanthophyceans)
  • Characteristic genus: Tribonema; group also referred to as Xantophytes

  • Occurrence: mostly freshwater and soil
  • Cell wall: cellulose, often H-shaped halves

  • Storage product: lipids in cytoplasmatic droplets
  • Pigments: Chl. a, c, diatoxanthin, diadinoxanthin, but fucoxanthin is lacking (appear yellow-green)
  • Appearance: unicellular flagellates, coccoid forms, filaments, siphonaceous coenocytes (tubular multi-nucleolate cells)

  • Asexual reproduction by nonflagellate autospores and aplanospores or flagellated zoospores; thick-walled cysts; 
  • Sexual reproduction by isogamy or oogamy; flagellate gametes have typical ochrophyte flagella; exception: Vaucheria with 4-flagella male gametes