A slime mold is often thought of as an organism that uses spores in order to reproduce, often resembling a gelatinous slime. They were once thought to be fungi, but are now known to be a separate group, with about 900 known species. Currently, they are divided into two groups—the true slime molds (Myxogastria) and the cellular slime molds (Dictyosteliomycota or, in part, Acrasiomycota). Of the latter, a cellular slime mold called Dictyostelium discoideum has been studied as a model for the developmental biology of complex organisms. Under the best conditions, this organism lives as individual, amoeboid cells. When food is scarce, the cells stream together into a moving mass resembling a slug that can change into a stalk with a spore-bearing body at its top. This structure then releases spores that can grow into a new amoeboid cell.