In true slime molds, or Mycetozoa, the feeding stage takes the form of a plasmodium, which is generally a multinucleate amoeba. These can grow up to several square feet in size and are frequently brightly coloured. New plamodia are formed by the fusion of biflagellate gametes, called swarmers.
In other groups, called cellular slime molds, sporangia are formed by aggregates of amoebae which come together under adverse conditions to form a colony resembling a slug. It crawls to a better location, and then forms a stalk-like fruiting body that releases spores (which will again exist as single-celled organisms until the next time they come under stress). This life cycle has appeared separately, with some differences in how it occurs, among the Dictyosteliida and Acrasids. It has also appeared among the Myxobacteria, though these are not normally considered cellular slime molds because they are prokaryotes rather than amoebae.
It has been observed that plasmodia can find the shortest route through a maze, by means of spreading out along all possible paths and then taking the best one; this is an interesting example of sophisticated information processing without a nervous system, emerging as a result of simple social behavior.
Slime molds are genuine cosmopolitans, existing all around us. They are rarely noticed though, since they are generally visible to the naked eye only as tiny humble sporangia, or the plasmodium clumping in preparation to production of sporangia.
Other forms sometimes referred to as slime molds include the Labyrinthulids and the Plasmodiophorids.
In Finland one particular unusually prominent slime mold with a yellow plasmodium (fuligo septimia) was supposedly used by witches to spoil a neighbours milk. The plasmodium was termed "paranvoi" (trans. butter of the familiar spirit).