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Definition: Slime Molds


Definition Slime Molds: Quite Tricky

In general, slime molds (mycetozoa) cannot be defined neither as a plant, nor as an animal, germ, fungus, nor as a protozoon. Slime molds form quasi an own category of organisms.


Why so?

As an explanation, I created a table to visualize the differences and commonalities:



Differences to slime molds

Commonalities with slime molds


  • No cells with chlorophyll (hence no photosynthesis)

  • no cell wall

  • no multicellular organisms

  • no blossoms, no pollination, no peduncle, no root

  • Locomotion



  • no limbs

  • no sub-division of the body
  • no multicellular organisms


  • Locomotion

  • no cell-wall (only cell membrane)

  • Locomotion can be compared to contraction of a muscle


  • no mycelium

  • no chitin

  • Locomotion

  • spore forming

  • live mainly in the wood

  • there are fungi with more than one cell nucleus in one cell


  • no flagellum (only in the state as Flagellat)

  • more than one cell nucleus

  • only one single cell

  • flagellum as Flagellat

  • Locomotion

  • mitotic cleavage

  • Phagocytosis


  • more than one cell nucleus (exception: certain algae)

  • only one single cell

  • similarity to amoeba

  • Phagocytosis

  • Forming of gametes

  • Gametes are protozoa

  • cell membrane as an outermost layer

  • Locomotion similar to those of amoeba

This table can be continued, I only summarized the most important facts.


So what is a slime mold?

Slime molds form an own group of organisms, which resembles, if anything, to the amoeba (slime molds are also called "social amoeba") and hence to the protozoa (as you can see in the table above, they have got most characteristics and the most important ones in common). A slime mold thus is kind of a giant amoeba with billions of cell nuclei.


How did these giant amoeba come into existence?

That is a big issue among scientists. Either slime molds originally have been multicellular organisms and their cell membranes vanished in the course of time, or they have been protozoa (single cellular organisms), whose nuclei proliferated without separation of the whole cell.


How does a slime mold look like?



Das ist ein Ausschnitt von Physarum polycephalum in einer Petrischale. Hübsch, nicht?


And where can these slime molds be found?

That is not easy to say. Someones can be found because of their eye-catching colors (red, yellow...), in the forest (mainly on dead, humid wood or leaves). Or they can be detected on manure piles, composts, bark mulch, ... Some species are inconspicuous, white colored or transparent or underground. Usually, only "slimy" slime molds (the plasmodial form) can be found in the nature, as the fruiting bodies are very small and difficult to find if you do not know what to look for.  


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