Opisthokont taxa

Holozoa () is a clade of organisms that includes animals and their closest single-celled relatives, but excludes fungi and all other organisms. Together they amount to more than 1.5 million species of purely heterotrophic organisms, including around 300 unicellular species. It consists of various subgroups, namely Metazoa (or animals) and the protists Choanoflagellata, Filasterea, Pluriformea and Ichthyosporea. Along with fungi and some other groups, Holozoa is part of the Opisthokonta, a supergroup of eukaryotes. Choanofila was previously used as the name for a group similar in composition to

The Filozoa are a monophyletic grouping within the Opisthokonta. They include animals and their nearest unicellular relatives (organisms which are more closely related to animals than to fungi or Mesomycetozoa).

Choanozoa is a clade of opisthokont eukaryotes consisting of the choanoflagellates (Choanoflagellatea) and the animals (Animalia). The sister-group relationship between the choanoflagellates and animals has important implications for the origin of the animals. The clade was identified in 2015 by Graham Budd and Sören Jensen, who used the name Apoikozoa. The 2018 revision of the classification first proposed by the International Society of Protistologists in 2012 recommends the use of the name Choanozoa.

Holomycota or Nucletmycea are a basal Opisthokont clade as sister of the Holozoa. It consists of the Cristidiscoidea, also called Nucleariidae, as well as the kingdom Fungi. Nucleariids are unicellular free-living phagotrophic amoebae, and are considered the earliest lineage of Holomycota. This suggests that animals and fungi independently acquired complex multicellularity from a common unicellular ancestor and that the osmotrophic lifestyle (one of the fungal hallmarks) was originated later in the divergence of this eukaryotic lineage. Opisthosporidians is a recently proposed taxonomic group

Opisthosporidia is a superphylum of intracellular parasites with amoeboid vegetative stage, defined as a common group of eukaryotic groups Microsporidia, Cryptomycota (also known as Rozellida, Rozellomycota, or Rozellosporidia) and Aphelidea. They have been considered to represent a monophyletic lineage with shared ecological and structural features, being a sister clade of the Fungi. Together with the Fungi they represent a sister clade of the Cristidiscoidea, together forming the Holomycota.