slime mould

 An unusual fungus-like protist of the phylum Myxomycota or the class Myxomycetes, having a stage of growth in which it comprises a naked noncellular multinucleate mass of creeping protoplasm having characteristics of both plants and animals; it also has a propagative phase in which it develops fruiting bodies bearing spores; it is sometimes classified as a protist. It is called also acellular slime mold.  [WordNet 1.5]

 Any of several remarkable amoebalike organisms of the phylum Acrasiomycota, mostly terrestrial, having a fruiting phase resembling that of the acellular slime molds, but being cellular and nucleate throughout their life cycle; called also cellular slime mold. The most studied species is Dictyostelium discoideum. In their feeding phase, they live like amoebae as individual cells, engulfing bacteria as a prime food source. When the food source diminishes, they begin to aggregate, swarming together to form clumps which may move toward heat and light, so as to reach the surface of the ground; they then differentiate into a form with spores contained within a sporangium resting on a stalk. When the spores are carried to another location with adequate food supplies, the spores may germinate to resume the life cycle. The phase of aggregation appears to be initiated by release of cyclic AMP, serving as a signal between the individual cells. The formation of the fruiting body has some similarities to differentiation in multicellular organisms, but the mechanisms are still under study. Some biologists object to the classification of Dictyostelium as a slime mold, as it is neither a mold nor slimy.  [PJC]