ACRASIDAE

Order of Protozoa also known as the cellular slime moulds. They normally exist as free-living phagocytic soil amoebae (vegetative cells), but when bacterial prey become scarce, they aggregate to form a pseudoplasmodium (cf. true plasmodium of Eumycetozoida), that is capable of directed motion. The grex, or slug, migrates until stimulated by environmental conditions to form a fruiting body or sorocarp. The slug cells differentiate into elongated stalk cells and spores, where the cells are surrounded by a cellulose capsule. The spores are released from the sporangium at the tip of the stalk and, in favourable conditions, an amoeba emerges from the capsule, feeds, divides and so establishes a new population. They can be cultured in the laboratory and are widely used in studies of cell-cell adhesion, cellular differentiation, chemotaxis and pattern formation. The commonest species studied are Dictyostelium discoideum, D. minutum, and Polysphondylium violaceum.