Holozoa is a group of organisms that includes

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s and their closest single-celled relatives, but excludes

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

. ''Holozoa'' is also an old name for the

tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

''Distaplia''.'' Because Holozoa is a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

including all organisms more closely related to animals than to fungi, some authors prefer it to recognizing

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

groups that mostly consists of Holozoa minus animals. Perhaps the best-known holozoans, apart from animals, are the choanoflagellates, which strongly resemble the collar cells of

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

s, and so were theorized to be related to sponges even in the 19th century. ''

Proterospongia ''Proterospongia'' is a genus of single-celled aquatic organisms which form colonies. It belongs to the choanoflagellate class. As a colony-forming choanoflagellate, ''Proterospongia'' is of interest to scientists studying the mechanisms of interce ...

'' is an example of a colonial choanoflagellate that may shed light on the origin of sponges. The affinities of the other single-celled holozoans only began to be recognized in the 1990s. The sub-classification Ichthyosporea or

Mesomycetozoea The Mesomycetozoea (or DRIP clade, or Ichthyosporea) are a small group of Opisthokonta in Eukaryota (formerly protists), mostly parasites of fish and other animals. Significance They are not particularly distinctive morphologically, appearing in ...

contains a number of mostly parasitic species. The amoeboid genera ''

Ministeria ''Ministeria'' is a genus of Filasterea. The species can be found in the North Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and ...

'' and ''

Capsaspora ''Capsaspora'' is a monotypic genus containing the single species ''Capsaspora owczarzaki. C. owczarzaki'' is a single-celled eukaryote that occupies a key phylogenetic position in our understanding of the origin of animal multicellularity, as o ...

'' may be united in a group called

Filasterea Filasterea is a proposed basal Filozoan clade that includes '' Ministeria'' and '' Capsaspora''. It is a sister clade to the Choanozoa in which the Choanoflagellatea and Animals appeared. Originally proposed by Shalchian-Tabrizi et al. in 2008 ...

by the structure of their thread-like

pseudopod A pseudopod or pseudopodium (plural: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filament ...

s. Along with choanoflagellates, filastereans may be closely related to animals, and one analysis grouped them together as the clade

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

Phylogeny

The

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

based on a 2011 multigene analysis is shown below. It is indicated how many million years ago (Mya) the clades diverged into newer clades. The holomycota tree is following Tedersoo et al. The alternative hypothesis is the teretosporea clade.

References

{{Taxonbar, from=Q1205110 Opisthokont unranked clades Ediacaran first appearances