Slime Mould - Taxonomy - Modern Classification

Modern Classification

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

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

  • Acrasids (Order Acrasida): 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. they used to belong to the defunct phylum of Acrasiomycota.
  • Plasmodiophorids (Order Plasmodiophorida): 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).
  • 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.
  • Fonticula is a cellular slime mold which forms a fruiting body in a volcano shape. Fonticula is not closely related to either the Dictyosteliida or the Acrasidae. A 2009 paper finds it to be related to Nuclearia, which in turn is related to fungi.
Grouping Genera Morphology
Amoebozoa > Conosa > Mycetozoa

Class Myxogastria: Cribraria, Lycogala, Tubifera, Echinostelium, Fuligo, Lepidoderma, Physarum, Comatricha, Stemonitis, Arcyria, Trichia

Syncytial or plasmodial slime molds

Class Dictyostelia: Dictyostelium, Polysphondylium, Acytostelium

Cellular slime molds

Class Protostelia: Planoprotostelium, Protostelium

Intermediate between myxomycetes and dictyostelids, but they are much smaller, the fruiting bodies only forming one to a few spores.
Rhizaria > Cercozoa > Endomyxa Class Phytomyxea: Lignieria, Membranosorus, Octomyxa, Phagomyxa, Plasmodiophora, Polymyxa, Sorodiscus, Sorosphaera, Spongospora, Tetramyxa, Woronina Parasitic protists which can cause cabbage club root disease and powdery scab tuber disease. They form coenocytes but are internal parasites of plants.
Excavata > Percolozoa > Heterolobosea Order Acrasida: Acrasis Cellular slime molds which have a similar life style to dictyostelids, but their amoebae behave differently, having eruptive pseudopodia.
Chromalveolate > Heterokontophyta > Labyrinthulomycetes Order Labyrinthulida: Labyrinthulids, Labyrinthula, Thraustochytrids, Aplanochytrium, Labyrinthuloides, Japonochytrium, Schizochytrium, Thraustochytrium, Ulkenia, Diplophryids, Diplophrys Slime nets which are marine and form labyrinthine networks of tubes in which amoeba without pseudopods can travel.
Fonticulida Fonticula Cellular slime mold which forms a fruiting body in a volcano shape.

Read more about this topic:  Slime Mould, Taxonomy

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