Holozoa

Holozoans Temporal range: Early Tonian - Present Pha. Proterozoic Archean Had.
Holozoan diversity. From top left corner: Capsaspora (Filasterea), Sphaeroforma (Ichthyosporea), Syssomonas (Pluriformea), Stephanoeca (Craspedida), Salpingoeca (Acanthoecida), Apis (Animalia)
Scientific classification
Domain:	Eukaryota
Clade:	Amorphea
Clade:	Obazoa
Clade:	Opisthokonta
Clade:	Holozoa Lang et al., 2002[1]
Clades[4]
Ichthyosporea (=Mesomycetozoea) Tunicaraptor[2] Pluriformea Corallochytrium Syssomonas Filozoa Filasterea Choanozoa Choanoflagellata Metazoa (=animals) Incertae sedis †Bicellum brasieri[3]
Synonyms
Choanofila Cavalier-Smith, 2009[5] (plus animals)

Holozoa (from Ancient Greek ὅλος (holos) 'whole' and ζῷον (zoion) 'animal') 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 Holozoa, but its usage is discouraged now because it excludes animals and is therefore paraphyletic.

The holozoan protists play a crucial role in understanding the evolutionary steps leading to the emergence of multicellular animals from single-celled ancestors. Recent genomic studies have shed light on the evolutionary relationships between the various holozoan lineages, revealing insights into the origins of multicellularity. Some fossils of possible metazoans have been reinterpreted as holozoan protists.