Agnotozoa is the name of a

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

of simple animals. The name first appeared in an invertebrate paleontology book as one of the "branches" of the subkingdom

Metazoa Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

. The branch contained only one group:

Mesozoa The Mesozoa are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells. A recent study recovered Mesoz ...

. More recently, some have used the name to refer to a sub-kingdom of three small phyla of simple animals without organs. These phyla are

Placozoa The Placozoa are a basal form of marine free-living (non-parasitic) multicellular organism. They are the simplest in structure of all animals. Three genera have been found: the classical ''Trichoplax adhaerens'', ''Hoilungia hongkongensis'', an ...

Orthonectida Orthonectida () is a small phylum of poorly known parasites of marine invertebrates that are among the simplest of multi-cellular organisms. Members of this phylum are known as orthonectids. Biology The adults, which are the sexual stage, are mi ...

, and

Rhombozoa Dicyemida, also known as Rhombozoa, is a phylum of tiny parasites that live in the renal appendages of cephalopods. Taxonomy Classification is controversial. Traditionally, dicyemids have been grouped with the Orthonectida in the Mesozoa, an ...

. They still have differentiated tissue, but that tissue is only organized in simple ways; for example, by being layered. The Orthonectida and Rhombozoa are also grouped into the Mesozoa. Biologists today generally do not use the taxon Agnotozoa. There are a few likely reasons for this. * There is doubt that placozoans are closely related to mesozoans. * There is doubt even that the two mesozoan groups (orthonectids and rhombozoans) are related to each other. * Even if the two mesozoan groups are related, there is little need for another name in addition to mesozoa. Wikispecies places the mesozoans in kingdom

protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...

References

* Obsolete animal taxa Subkingdoms {{animal-stub