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Cryptophytes
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Characteristic
genus: Cryptomonas
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Abundant
in freshwater and marine systems
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Appearance:
small (3-50 µm) biflagellate cells
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Flagella
emerging from apical depression (vestibulum)
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Auxotrophic:
at least one vitamin B is required
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Pigments:
Chl.a, c, a- and b-carotene, alloxanthin, phycoerythrin or phycocyanin
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Phycobilins
are not organized in phycobilisomes as in cyanobacteria and red algae but
are located within the
lumen of the thyllacoids
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Secondary
plastids with nucleomorph
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Storage
product: starch
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Heterotrophic,
uncolored forms with colorless plastids or without plastids
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Periplast:
organic plates underneath cell membrane
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Ejectisomes:
large, ejectile organelles along the vestibulum; discharged upon disturbance,
e.g. grazer, attack, change in pH, temperature, osmotic pressure
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Flagella
carry 1.5 µm long hairs and organic scales; hairs are thought to
increase flagella efficiency in swimming; long hairs = mastigonemes
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Flagellar
apparatus: cluster of posteriorly directed
microtubuli called rhizostyle
Reproduction
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Asexual
reproduction by mitosis and cytokinesis, cells
continue to swim
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Plastids:
nucleomorph is
divided prior to mitosis; nucleomorphes move to opposite ends of the plastid
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Mitosis:
partial breakdown of nuclear envelope and division spindle at the cell
poles
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Cytokinesis:
along cell axis, starting from posterior end (in contrast to Euglenophytes!)
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Resting
cysts: round, thick extracellular matrix,
pink color
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Sexual
reproduction observed in some species: Proteomonas
exhibits two morphologically distinct growth forms, one of which possessestwice
the DNA amount
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Gamete
fusion not observed in Proteomonas,
but in Chroomonas acuta: isogamy, flagella of gametes are not
involved in fusion as is thecase in other algal groups
Cryptophyte Ecology
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Occurrence:
particularly in oligotrophic lakes and oceans
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Temperature
range: prefer temperate and high-latitude
environments, rarely at temperatures above 20°C
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Significance:
can form substantial part (up to 70%) of phytoplankton in Antarctic lakes
and winter/early spring communities in the North and Baltic Seas
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Depth
distribution: in lakes typically at greater
depths, forming a subsurface chlorophyll maximum
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Nutrition:
use organic forms of nitrogen and ammonium, low uptake capacities for
nitrate
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Phagotrophy
and Osmotrophy
has been demonstrated for at least some species
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Endosymbionts
in the marine, olbigate phototrophic ciliate Mesodinium
rubrum, which can produce red-colored,
non-toxic blooms in upwelling areas
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