Fungi can be unicellular as yeasts, or develop a network of filaments called a mycelium, which is often described as mold. Fungi that feed on decaying and dead matter are termed saprobes.

External enzymes called exoenzymes digest nutrients that are absorbed by the body of the fungus, which is called a thallus. Fungi are eukaryotic organisms that appeared on land more than 450 million years ago, but clearly have an evolutionary history far greater.

saprobe — organism that derives nutrients from decaying organic matter; also saprophyte. mold — tangle of visible mycelia with a fuzzy appearance. yeast — general term used to describe unicellular fungi. thallus — vegetative body of a fungus.