Choanozoa is the name of a phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 of protist

Protist

Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...

s that belongs to the line of opisthokont

Opisthokont

The opisthokonts or "Fungi/Metazoa group" are a broad group of eukaryotes, including both the animal and fungus kingdoms, together with the eukaryotic microorganisms that are sometimes grouped in the paraphyletic phylum Choanozoa...

s.

Most appear closer to the animals than to the fungi, and they are of great interest to biologists studying animal origins.

The nucleariid

Nucleariid

The nucleariids are a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the similar vampyrellids mainly by having mitochondria with discoid cristae.-Classification:...

s seem to be a sister group to the fungi, and as such tend to be excluded from the Choanozoa.

Choanozoa have been described as possessing a posterior cilium

Cilium

A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....

.

Cladogram

The great kingdoms and their close relatives.

Classification

The Choanozoa consist of at least three groups: (1) the Mesomycetozoea

Mesomycetozoea

The Mesomycetozoea are a small group of protists, mostly parasites of fish and other animals.-Significance:...

 (Ichthyosporea), a group of parasites infecting fish and other animals, (2) a group described in the early 21st century including Ministeria

Ministeria

Ministeria is a small single-celled eukaryote which feeds on bacteria. Although it is an opisthokont, it seems not to fit in any of the established opisthokont lineages such as choanoflagellates or animals. It might form a group with Capsaspora, another opisthokont of uncertain placement....

and Capsaspora

Capsaspora

Capsaspora is a single-celled eukaryote which is a symbiont in the haemolymph of the tropical freshwater snail Biomphalaria glabrata.- Taxonomy :...

, which has been named Filasterea

Filasterea

Filasterea is a grouping that includes Ministeria and Capsaspora....

 after the thread-like tentacles which both genera share, and (3) the choanoflagellate

Choanoflagellate

The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals...

s including Monosiga and Proterospongia

Proterospongia

Proterospongia is a genus of choanoflagellate, notable for its formation of colonies. As a colony-forming choanoflagellate, Proterospongia is of interest to scientists studying the mechanisms of intercellular signaling and adhesion present prior to the origin of animals.-Physical...

. The position of Corallochytrium

Corallochytrium

Corallochytrium is a single-celled eukaryote which was found in coral reef lagoons of the Lakshadweep islands of the Arabian sea. Although it is an opisthokont, its closest relatives in that group are not clear. For example, it is not clear whether it is more closely related to animals or...

is unclear.

The Choanozoa appear to be a paraphyletic group which gave rise to the animals. Lang et al. (2002) propose the new name Holozoa

Holozoa

Holozoa is a group of organisms that includes animals and their closest single-celled relatives, but excludes fungi. Holozoa is also an old name for the tunicate genus Distaplia....

 for a monophyletic grouping which is, in effect, Choanozoa enlarged or redefined to include animals.