INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

PROTOZOA

SARCODINES

PHYLUM AMOEBOZOA

CLASS MYCETOZOA

SUBCLASS MYXOGASTRIA

The largest subclass comprises about 800 species. Myxogastrians differ from other slime Molds in that their vegetative body is a true multinucleated plasmodium ranging from 0.1 to 20 cm or even more in size. The plasmodium actively moves toward food, phagocytosing Bacteria, Protozoa, Algae, fungal spores, and organic debris, while avoiding light (negative phototaxis). During sporulation, the plasmodium reverses its negative phototaxis to positive, crawling out onto a brightly lit surface where spore-bearing fruiting bodies are formed. The plasmodium is diploid, and a reduction division of nuclei occurs during sporulation. Under favorable conditions, the spores give rise to haploid biflagellate zoospores or myxamoebae, which functionally act as Gametes as they immediately copulate to form a diploid myxamoeba; from this, through multiple mitotic nuclear divisions and cytoplasmic growth, a new plasmodium is formed. Thus, myxogastrians are characterized by a life cycle with gametic chromosome reduction.

Myxogastrians inhabit decaying wood, under the bark of dead trees, in leaf litter, and in soil. A representative of this subclass is Lycogala epidendrum, which forms coral-red plasmodia up to several centimeters in size on tree stumps. Its hemispherical fruiting bodies, about 1.5 cm in size, form dense clusters (Fig. 24).

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Fig. 24. Fruiting bodies of Lycogala epidendrum (adapted from Horlenko)