Slime molds are a group of organisms that possess both animal and plant like characteristics. They can be broken down into two main groups: cellular slime molds (Arasiomycetes) and plasmodial (or true) slime molds (Myxomycetes).
Arasiomycetes
In its feeding stage, the cellular slime mold is a uninucleate amoeba with no true cell walls. When food runs out, a chemical is secreted which causes the separate amoebas to congregate into a pseudoplasmodium, then form a fruiting body, which contains spores with cellulose walls. When released, the spores (which were produced by meiosis) form new myxoamoebas. Sexual reproduction has been observed, but only recently, and is much different than the asexual reproduction of the fruiting bodies.
Myxomycetes
In its feeding stage, the plasmodial slime mold is a coenocytic structure called a plasmodium, formed by the fusion of many small plasmodia. The plasmodium is mulitnucleate and has no true cell walls. In food shortages, myxomycetes turn into a fruiting body with cell walls. Inside, meiosis produces spores, which, when released, form haploid amoebas, possibly with flagella. Some amoebas or flagellated cells (swarm cells) fuse to form a diploid cell, which, through mitosis, forms a plasmodium.
Slime molds can usually be found in soil, wood, dung, or decaying vegetation where, in their feeding stage, they move around (although very slowly) and engulf bacteria, food particles, and other organic matter. Thus, the slime mold acts as a decomposer in the ecosystem, but also as a consumer, as it eats bacteria. At the end of most food chains, the slime mold regenerates consumers waste, allowing plants to re-use the nutrients.
Slime molds pose a problem for the field of taxonomy. As can be seen simply by looking at life cycle diagrams, a slime mold may exist as a mobile, amoeba-like organism, which feeds by engulfing material; or as a reproductive structure, which may have a stalk, and produces spores. The former phase of life of the slime mold leans toward the Kingdom Protista, while the latter resembles a fungus. Presently, however, slime molds are classified as protista.
REFERENCES
Biology, Third Edition, CBS College Publishing, 1987
Biology: A Journey Into Life, Third Edition, Saunders College Publishing, 1994