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Ulvophyceae
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Most
conspicous green algal seaweeds (Ulva,
Enteromorpha)
in marine systems
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Coralline
green alga (Halimeda, Cymopolia);
remains form up to 50 m thick layers in sediments at the Great Barrier
Reef, Australia
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Filamentous
and unicellular
forms in freshwater and marine systems
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Siphonaceous
forms (siphon = tube) of spectacular morphological differentiation
(Acetabularia)
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Earliest
evolutionary form of UTC cluster; gametes
sometimes with small scales ressembling prasinophyceans
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Major
groups:
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Ulotrichales:
unicells, filaments, simple life cycle
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Ulvales:
uninucleate cells, alternation of 2 multicellular generations
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Siphonocladales:
multinucleate cells, not siphonous
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Dasycladales,
Caulerpales:
siphonous forms
Ulothrichales
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Morphologically
diverse group of flagellates, non-flagellated
unicells, unbranched and branched filaments; uninucleate and multinucleate
cells, blades of single-layer uninucleate cells
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Life
cycle shows only the zygote as diploid stage
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Codiolum
stage: sac-like, unicellular, thick-walled stage attached to substrate;
can survive period of dormancy
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Haploid
zoospores (meiospores) are produced from the
codiolum stage and form the vegetative, haploid gametophyte
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The genus
Codiolum:
the reproductive codiolum stage is named after the genus Codiolum,
because the zygote stage ressembles this genus; however, it appears that
most occurrences of Codiolum in nature are rather codiolum stages
of other ulotrichales algae
Ulvales
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Named
after
the common sea lettuce Ulva
left three: Enteromorpha; right:
Percursaria (biseriate filaments)
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Uninucleate
cells with one chloroplast
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Life
cycle with two macroscopic generations; biflagellate,
naked gametes; quadriflagellate, naked zoospores (meiospores)
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Isomorphic
generations, i.e. sporo- and gametophyte look
alike
Siphonocladales (syn.
Cladophorales)
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Multinucleate
cells forming branched filaments or pseudoparenchymatous
blades
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Cell
division uncoupled from mitosis; septum (cross-wall)
formation by furrowing
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Reticulated
plastid or many small discoid plastids with
pyrenoids
Caulerpales
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Named
after
the genus Caulerpa
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Siphonous,
multinucleate marine macroalgae
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One large
cell – vulnerable to substantial plasma loss
upon damage; wound-healing occurs in seconds, involving actin-mediated
contraction and a plug of cell wall material
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Amyloplasts:
unpigmented plastids for starch storage
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Sexual
reproduction: anisogamy, biflagellate gametes;
life history poorly understood; quadriflagellated zoospores rare
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Derbesia-Halicystis
life cycle: heteromorphic life cycle, sporophyte
and gametophyte of Halicystis has been described as different species
(Derbesia)
Dasycladales
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Small
group (19-50 species) of marine macroalgae
of shallow, tropical and subtropical waters
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Siphonous
vegetative thalli with basical holdfast
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Nucleus
located in holdfast, diploid or polyploid
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Thin
layer of plasma with large central vacuole
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Starch
is stored in plastid and in the cytoplasma
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Reproduction
by biflagellate gametes produced in small spherical, walled cysts
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Meiosis
of the central nucleus occurs sometime prior to the onset of reproductive
development
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Mitotic
divisions produce hundreds of secondary nuclei,
which are transported by plasma flow to the reproductive part of the
thallus to form gametes
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The
Mermaid‘s Wine Glass:
Hämmerlings reconstruction experiments
in the 1930‘s
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Regeneration
of the head only occurs in the section carrying
the nucleus --> thallus regeneration is under the control of the nucleus
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Morphology
of the head: stems of two different species with different head morphology
are plugged on nucleus-carrying holdfast of two species; the new head corresponds
to the species of the nucleus --> head morphology is controlled by the
nucleus
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Gamete
production: stem and head of species 2 are
plugged on holdfast of species 1; micronuclei and gametes are formed within
the new (species 2) head by the nucleus of species 1
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