Plasmodial slime molds
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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

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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

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  • Mycetozoa = cellular, plasmodial slime molds plus protostelids

  • Cellular slime molds and protostelids now placed in phylum Myxomycota

  • Names imply a fungal-like affinity

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  • Myxomycetes--5 orders, 13 families, 62 genera, 800 species

  • Characterized by plasmodium

    • Engulfs bacteria, fungal spores, small pieces of organic matter

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Physarum life cycle




Synchronous mitotic divisions


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Stages in Life Cycle

  • Spores (2nn)

    • 4-20 µm, pigmented ornamented; meiosis in spore = 4 nuclei; 3 degenerate

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Stages in Life Cycle

  • Myxamoebae (n)

    • feed, divide, convert to swarm cells, function as gametes; form microcysts under adverse conditions MISCE2002/myxamo2.jpg

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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

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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

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Stages in Life Cycle

  • Sporophore (2n)

    • Entire plasmodium is converted into sporophore(s)

  • Sclerotium or macrocyst (2n)

    • Resistant stage formed by plasmodium

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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

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  • 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

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Capillitium (top left; photo by David Geiser)

Pseudocapillium (top right; photo from Fifth Kingdom)

Elaters (bottom left) Myxomycota/elaters.jpg

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Sporocarp—stalked or sessile

May have columella 

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  • Large, cushion-shaped sporophore, one per plasmodium

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  • Cluster of sporophores grouped tightly together

Photo by David Geiser

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  • 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 l.jpg
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 l.jpg
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 l.jpg
Physarales--Purplish-brown spores, usually with abundant and conspicuous lime on or in sporophore




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Stemonitales--Violet-brown spores, lime absent conspicuous lime on or in sporophore



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Photo by Stephen Sharnoff conspicuous lime on or in sporophore


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

Photo by Stephen Sharnoff

Photo by David Geiser

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Protostelids protostelids (one genus,

  • 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

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Protostelid Life Cycle protostelids (one genus,

  • 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

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Life cycle of simple protostelid protostelids (one genus,

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Life cycle of complex protostelid protostelids (one genus,