When the first slime moulds were described by Johann H. F. Link in 1833, they were given the term myxomycetes (Gr. myxa = slime). Link used the suffix -mycetes because of the superficial similarity of the fructifications of slime moulds with the fruit bodies of certain fungi, notably Gasteromycetes (see Chapter 20). Although it has been appreciated for some time that they lack any true relationship with the Eumycota (de Bary, 1887; Whittaker, 1969), slime moulds have none the less been studied mainly by mycologists rather than protozoologists, probably because they occur in the same habitats as fungi and are routinely encountered during fungus forays. Since slime moulds are only rarely covered by zoology courses even today, they are briefly described in this chapter, referring to more specialized literature as appropriate.
Slime moulds differ substantially from the Eumycota not only in phylogenetic terms, but also regarding their physiology and ecology. Their vegetative state is that of individual amoebae in the cellular slime moulds, or of a multinuclear (coenocytic) plasmodium in the plasmodial slime moulds. Motile stages bearing usually two anterior whiplash-type flagella may be present in the plasmodial slime moulds (Sections 2.4, 2.5) and in the Plasmodiophoromycota (Chapter 3). Amoebae or plasmodia feed by the ingestion (phagocytosis) of bacteria, yeast cells or other amoebae. This is followed by intracellular digestion in vacuoles. The mode of nutrition in slime moulds is therefore fundamentally different from extracellular degradation and absorption as shown by Eumycota.