An acrasin is a pheromone used by species of slime mold, which signals to the many individual cells and triggers an aggregation response, such that they form a single large cell. One of the earliest acrasins to be identified was cyclic AMP, found in the species Dictyostelium discoideum by Brian Shaffer, which exhibits a complex swirling-pulsating spiral pattern when forming a pseudoplasmodium.