Among the Myxomycetes, or true slime molds, the feeding stage takes the form of a multinucleate amoeboid called a plasmodium. These can grow in size up to several square feet and are frequently brightly colored. New plasmodia are formed by the fusion of biflagellate gametes, called swarmers, released from the spores. The Protostelida are similar, but new amoebae remain mononucleate and do not develop into plasmodia.
Cellular slime molds start out as individual amoebae. Under adverse conditions, though, they attract to one another and pile up to form a pseudoplasmodium or "slug". Although the cells are still capable of functioning independently - a slug will come apart if it is shaken hard enough, and the amoebae will resume feeding - it has a distinct front and back end, and after a few days differentiates to form a sporangium. This life cycle has evolved several times - among the Dictyosteliida, and Acrasida, and actually among a group of prokaryotes called the Myxobacteria.