Eumycetozoa

Evolution

Eumycetozoa is a well supported clade within Amoebozoa. In independent phylogenetic analyses, it has been consistently recovered as the sister group to Archamoebae. The Eumycetozoa+Archamoebae clade is, in turn, the sister group to Variosea. Within Eumycetozoa, Dictyostelia has a basal position while Myxogastria and Protosporangiida form a clade. Together, these three groups are part of the larger clade Conosa. The following cladogram is based on a 2022 analysis:

Taxonomy

The name Eumycetozoa was first used by German mycologist Friedrich Wilhelm Zopf in 1884, although no formal taxonomic rank was given. In 1975, mycologist Lindsay Shepherd Olive reintroduced the name Eumycetozoa as a class containing the three groups of fruiting amoebae traditionally included in this taxon: Myxogastria, Dictyostelia and Protostelia. Olive hypothesized that all fruiting amoebae were grouped by this monophyletic taxon, and that the Myxogastria and Dictyostelia were also monophyletic taxa that evolved from a paraphyletic grade of Protostelia. This definition of Eumycetozoa, which included protostelids, was maintained in the 2005 cladistic classification of eukaryotes, where the name was synonymized with Mycetozoa.

• Amoebozoa Lühe, 1913, emend. Cavalier-Smith, 1998
  • Eumycetozoa Zopf, 1884, emend. L.S.Olive, 1975 [=Mycetozoa de Bary, 1873]
    • Protostelia L.S. Olive, 1975 (P)
    • Myxogastria Macbride, 1899 [=Myxomycetes Link, 1833, emend. Haeckel, 1866]
    • Dictyostelia Lister, 1909, emend. L.S.Olive, 1970
    • Incertae sedis Eumycetozoa: Copromyxa, Copromyxella, Fonticula

However, studies in the 2000s decade disproved this hypothesis. Both morphological and molecular studies showed that Eumycetozoa includes a number of non-fruiting amoeboid groups. More importantly, the Protostelia were discovered to be polyphyletic. The protosteloid type of fruiting body formation, initially considered the ancestral feature shared between all Eumycetozoa, has evolved independently at least in eight lineages within Amoebozoa (e.g. soliformoviids, cavosteliids, schizoplasmodiids, protosporangiids). This discovery lead to the conclusion that the entirety of Amoebozoa became a synonym of Eumycetozoa, and was treated as such in the 2012 cladistic classification of eukaryotes. The term Amoebozoa was conserved as a familiar well-established name of popular usage, despite the term Eumycetozoa having priority as the older name.

To preserve this widely used name, biologist Seungho Kang and his coauthors redefined Eumycetozoa in 2017 to include only one group of protosteloid amoebae, the Protosporangiida (also known as Ceratiomyxomycetes), which are a monophyletic taxon. This usage corresponds to the 1975 hypothesis from Olive that postulates a clade of exclusively fruiting protists that includes myxogastrids, dictyostelids, and some protosteloid amoebae (in this case, the protosporangiids). As of 2019, this renewed definition is accepted by the scientific community and appears in the modern cladistic classification of eukaryotes, revised by the International Society of Protistologists. The name Macromycetozoa was suggested earlier, but Eumycetozoa was chosen for being the oldest term.

• Amoebozoa Lühe, 1913, emend. Cavalier-Smith, 1998
  • Evosea Kang et al. 2017
    • Eumycetozoa Zopf 1884 ex L.S. Olive, sensu Kang et al. 2017 [=Macromycetozoa Fiore-Donno et al. 2010]
      • Dictyostelia Lister 1909, sensu Sheikh et al. 2018
      • Myxogastria Macbride 1899 [=Myxomycetes Link 1833, sensu Haeckel 1866]
      • Protosporangiida Shadwick & Spiegel in Adl et al. 2012

The name Mycetozoa was maintained in traditional classifications by some authors like Thomas Cavalier-Smith, who also used a renewed definition to include only protosporangiids. However this scheme did not acquire wide usage.