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  • Most conspicous green algal seaweeds (Ulva, Enteromorpha) in marine systems
  • Coralline green alga (Halimeda, Cymopolia); remains form up to 50 m thick layers in sediments at the Great Barrier Reef, Australia
  • Filamentous and unicellular forms in freshwater and marine systems
  • Siphonaceous forms (siphon = tube) of spectacular morphological differentiation (Acetabularia)
  • Earliest evolutionary form of UTC cluster; gametes sometimes with small scales ressembling prasinophyceans
  • Major groups:
    • Ulotrichales: unicells, filaments, simple life cycle
    • Ulvales: uninucleate cells, alternation of 2 multicellular generations
    • Siphonocladales: multinucleate cells, not siphonous
    • Dasycladales, Caulerpales: siphonous forms
  • Morphologically diverse group of flagellates, non-flagellated unicells, unbranched and branched filaments; uninucleate and multinucleate cells, blades of single-layer uninucleate cells

  • Life cycle shows only the zygote as diploid stage

  • Codiolum stage: sac-like, unicellular, thick-walled stage attached to substrate; can survive period of dormancy
  • Haploid zoospores (meiospores) are produced from the codiolum stage and form the vegetative, haploid gametophyte
  • 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

  • Named after the common sea lettuce Ulva

  • left three: Enteromorpha; right: Percursaria (biseriate filaments)
  • Uninucleate cells with one chloroplast
  • Life cycle with two macroscopic generations; biflagellate, naked gametes; quadriflagellate, naked zoospores (meiospores)

  • Isomorphic generations, i.e. sporo- and gametophyte look alike
Siphonocladales (syn. Cladophorales)
  • Multinucleate cells forming branched filaments or pseudoparenchymatous blades

  • Cell division uncoupled from mitosis; septum (cross-wall) formation by furrowing
  • Reticulated plastid or many small discoid plastids with pyrenoids

  • Named after the genus Caulerpa

  • Siphonous, multinucleate marine macroalgae
  • 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
  • Amyloplasts: unpigmented plastids for starch storage
  • Sexual reproduction: anisogamy, biflagellate gametes; life history poorly understood; quadriflagellated zoospores rare
  • Derbesia-Halicystis life cycle: heteromorphic life cycle, sporophyte and gametophyte of Halicystis has been described as different species (Derbesia)
  • Small group (19-50 species) of marine macroalgae of shallow, tropical and subtropical waters
  • Siphonous vegetative thalli with basical holdfast
  • Nucleus located in holdfast, diploid or polyploid
  • Thin layer of plasma with large central vacuole
  • Starch is stored in plastid and in the cytoplasma
  • Reproduction by biflagellate gametes produced in small spherical, walled cysts
  • Meiosis of the central nucleus occurs sometime prior to the onset of reproductive development
  • Mitotic divisions produce hundreds of secondary nuclei, which are transported by plasma flow to the reproductive part of the thallus to form gametes

  • The Mermaid‘s Wine Glass: 
    Hämmerlings reconstruction experiments in the 1930‘s
    • Regeneration of the head only occurs in the section carrying the nucleus --> thallus regeneration is under the control of the nucleus
    • 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
    • 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