Physarum polycephalum is a large, yellow slime mold that is commonly studied in laboratories due to its ease to culture and highly visible cytoplasmic streaming. The organism is essentially a giant multi-nucleated, unicellular protist stretching up to hundreds of squared centimeters. There are no cell walls or membrane separating the nuclei. It uses tubular elements, chemical signals and circulating nutrients to form pseudopods that allow it to navigate in the environment. They can digest solid food similar to an amoeba or secret enzymes and absorb the nutrients. They feed on bacteria, protozoa, fungal spores, and other decaying organic material.

Under adverse conditions, sclerotia (hardened resting structures of irregular form consisting of minute cell-like components). Once favourable conditions return, the sclerotia are converted back to the active growing plasmodium stage. Under conditions of starvation and sunlight, fruiting bodies form that release haploid spores. When moist conditions return, the spores will germinate as either amoeboid cells or as flagellates (if they germinate in a liquid environment). Two haploid amoeboid cells and their nuclei can fuse to begin growth into the multinucleated (with diploid nuclei) plasmodium. 

P. polycephalum is used for motility, cellular differentiation, chemotaxis and problem solving studies. However, they are also used for studies of RNA editing as it is the only organism known to edit RNA by both insertion and substitution of nucleotides.