The following moderators provide knowledge and expertise for Slime Moulds (Myxomycetes):
Slime moulds are classified as Protista (or Protocista). They are neither plants, animals nor fungi. Slime moulds are peculiar protists that normally take the form of amoeba but also develop fruit bodies that release spores, and are superficially similar to the sporangia of fungi. Read more about them on the Fungimap page: https://fungimap.org.au/about-fungi/2126-2/
There are 2 types of Slime Moulds: Cellular Slime Moulds, which are rarely seen because of their small size, and Plasmodial Slime Moulds, which are larger, making them easier to observe.
In Plasmodial Slime Moulds you will generally see either the plasmodium stage of the life cycle, during which the slime mould feeds on decaying organic matter and other minute organisms, or the spore formation stage (or fruiting bodies).
For beginners, here is a “A Key to Common Genera of Slime Moulds” written and illustrated by Peta McDonald, a Melbourne science teacher: https://upload.wikimedia.org/wikipedia/commons/f/f6/A_Key_to_Common_Genera_of_Slime_Moulds.pdf
A more technical key can be found in “Taxonomic Keys and Plates from The Myxomycetes”, a book by George W. Martin and Constantine J. Alexopoulos: https://www.myxotropic.org/wp-content/uploads/2021/04/MyxoKeys.pdf
For a photo gallery of slime moulds from around the world check out this one on a Spanish myxomycetes website: https://www.myxotropic.org/galeria/