Life cycle of Physarum . Spores germinate in the presence of water and liberate one or more amoeboid swarm cells, each bearing two unequal anterior whiplash flagella. Swarm cells fuse and become zygotes or withdraw their flagella and become myxamoebae. In homothallic species all gametes are compatible and any two may fuse. Those with different alleles will fuse.
Zygotes then form multinucleate protoplasmic masses, known as plasmodia.
Chemical changes trigger a plasmodium to form fruiting bodies, differentiate into a sporophore and produce sporangia. The cells in the sporangia undergo meiosis and become mature haploid spores.