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Plasmodial Slime Molds. Pl P 421/521. Ribosomal RNA phylogenies place slime molds as unrelated, early branching eurkaryote lineages . Baldauf and Doolittle, 1997. PNAS 94 (22): 12007-12012.

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Ribosomal RNA phylogenies place slime molds as unrelated, early branching eurkaryote lineages


Baldauf and Doolittle, 1997. PNAS 94 (22): 12007-12012

Actin, elongation factor, and β-tubulin phylogenies place the plasmodial and cellular slime molds as a monophyletic group close to Animal + FungI

  • Mycetozoa = cellular, plasmodial slime molds plus protostelids
  • Cellular slime molds and protostelids now placed in phylum Myxomycota
  • Names imply a fungal-like affinity
  • Myxomycetes--5 orders, 13 families, 62 genera, 800 species
  • Characterized by plasmodium
    • Engulfs bacteria, fungal spores, small pieces of organic matter
physarum life cycle
Physarum life cycle




Synchronous mitotic divisions


stages in life cycle
Stages in Life Cycle
  • Spores (2nn)
    • 4-20 µm, pigmented ornamented; meiosis in spore = 4 nuclei; 3 degenerate
stages in life cycle8
Stages in Life Cycle
  • Myxamoebae (n)
    • feed, divide, convert to swarm cells, function as gametes; form microcysts under adverse conditions MISCE2002/myxamo2.jpg

stages in life cycle9
Stages in Life Cycle
  • Swarm cells (n)
    • 1-4 anterior whiplash flagella, amoeboid posterior; feed (absorption and engulfment), function as gametes
    • can’t undergo cell division

stages in life cycle10
Stages in Life Cycle
  • Zygote (2n)
    • Formed by fusion of myxamoebae or swarm cells; enlarges through synchronous nuclear division
  • Plasmodium (2n)
    • Multinucleate, wall-less protoplasm

Photo by Stephen Sharnoff

stages in life cycle11
Stages in Life Cycle
  • Sporophore (2n)
    • Entire plasmodium is converted into sporophore(s)
  • Sclerotium or macrocyst (2n)
    • Resistant stage formed by plasmodium
types of plasmodia
Types of plasmodia
  • Phaneroplasmodium
    • Conspicuous, often colored, with protoplasm forming veins with reversible streaming
  • Aphanoplasmodium
    • With a network of fine, transparent threads and homogenous protoplasm
  • Protoplasmodium
    • Microscopic, with homogenous protoplasm, giving rise to one sporophore
  • Mass of spores formed inside peridium, spores intermingled with:
    • Capillitium
      • threadlike, often ornamented
    • Elaters
      • Threadlike, ornamented, not connected at ends
    • Pseudocapillitium
      • Threads, bristles, membrane or platelike network
  • Lime may be present on peridium, stalk, columella or capillitium, or nodes of pseudocapillitum

Capillitium (top left; photo by David Geiser)

Pseudocapillium (top right; photo from Fifth Kingdom)

Elaters (bottom left) Myxomycota/elaters.jpg

sporocarp stalked or sessile
Sporocarp—stalked or sessile

May have columella 

  • Large, cushion-shaped sporophore, one per plasmodium
  • Cluster of sporophores grouped tightly together

Photo by David Geiser

  • Sporophore developing along veins of phaneroplasmodium; takes on reticulate shape of veins
liceales pale or brown spores capillitium and lime absent pseudocapillitium may be present
Liceales-- Pale or brown spores, capillitium and lime absent, pseudocapillitium may be present



Photo by Stephen Sharnoff

trichiales pale spores yellow orange or red and abundant conspicuous capillitium
Trichiales--Pale spores (yellow, orange or red) and abundant, conspicuous capillitium



physarales purplish brown spores usually with abundant and conspicuous lime on or in sporophore
Physarales--Purplish-brown spores, usually with abundant and conspicuous lime on or in sporophore




ceratiomyxales exosporous sporophores probably belongs in protostelids one genus ceratiomyxa
Ceratiomyxales--Exosporous sporophores; probably belongs in protostelids (one genus, Ceratiomyxa)

Photo by Stephen Sharnoff

Photo by David Geiser

  • Simplest known slime molds
  • Discovered in 1970
    • Easily mistaken for mucoraceous fungi or deuteromycetes
  • In dead, attached plant parts, herbivore dung or soil; feed on bacteria, yeast and fungal spores
  • 14 genera and 32 species
protostelid life cycle
Protostelid Life Cycle
  • Amoeboid cells (filose pseudopodia) become one or more prespore cells that rise on stalk and encyst to form one to four spores
  • Plasmodium and flagellated cells present in “complex” life cycles
  • Sexual reproduction not known

Life cycle of simple protostelid


Life cycle of complex protostelid