Amoebozoan slime molds[edit]

In more strict terms, slime molds comprise the amoebozoan group of the mycetozoans. Mycetozoa, which includes the defunct phylum Myxomycota (now Myxogastria), includethe following three groups:

• Myxogastria or myxomycetes: syncytial or plasmodial slime molds
• Dictyosteliida: cellular slime molds or dictyostelids.
• Protostelids.

Even at this level of classification there are conflicts to be resolved. Recent molecular evidence shows that the first two groups are likely to be monophyletic and the protostelids however to be polyphyletic. For this reason, scientists are currently trying to understand the relationships among these three groups.

The most commonly encountered are the Myxogastria. A common slime mold which forms tiny brown tufts on rotting logs is Stemonitis. Another form which lives in rotting logs and is often used in research is Physarum polycephalum. In logs it has the appearance of a slimy web-work of yellow threads, up to a few feet in size. Fuligo forms yellow crusts in mulch.

The Dictyosteliida, cellular slime molds, are distantly related to the plasmodial slime molds and have a very different lifestyle. Their amoebae do not form huge coenocytes, and remain individual. They live in similar habitats and feed on microorganisms. When food runs out and they are ready to form sporangia, they do something radically different. They release signal molecules into their environment, by which they find each other and create swarms. These amoeba then join up into a tiny multicellular slug-like coordinated creature, which crawls to an open lit place and grows into a fruiting body. Some of the amoebae become spores to begin the next generation, but some of the amoebae sacrifice themselves to become a dead stalk, lifting the spores up into the air.

The Protostelids have characters intermediate between the previous two groups, but they are much smaller, the fruiting bodies only forming one to a few spores.

Non-Amoebozoan slime molds[edit]

• Acrasiomycota: slime molds which belong to the Heterolobosea within the super group Excavata. They have a similar life style to Dictyostelids, but their amoebae behave differently, having eruptive pseudopodia.
• Labyrinthulomycota: slime nets which belong to the super group Chromalveolata as the class Labyrinthulomycetes. They are marine and form labyrinthine networks of tubes in which amoeba without pseudopods can travel.
• Plasmodiophorids: parasitic protists which belong to the super group Rhizaria. They can cause cabbage club root disease and powdery scab tuber disease. The Plasmodiophorids also form coenocytes but are internal parasites of plants (e.g., Club root disease of cabbages).
• Fonticula is a cellular slime mold which forms a fruiting body in a volcano shape.^[1] Fonticula is not closely related to either the Dictyosteliida or the Acrasidae.^[2] A 2009 paper finds it to be related to Nuclearia, which in turn is related to fungi.^[3]