Agnotozoa
Encyclopedia
Agnotozoa is the name of a taxon
of simple animals. The name first appeared in an invertebrate paleontology book as one of the "branches" of the subkingdom Metazoa. The branch contained only one group: Mesozoa
.
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, Orthonectida
, and Rhombozoa
. 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.
Wikispecies places the mesozoans in kingdom protista.
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
of simple animals. The name first appeared in an invertebrate paleontology book as one of the "branches" of the subkingdom Metazoa. The branch contained only one group: Mesozoa
Mesozoa
The Mesozoa are enigmatic, minuscule, worm-like parasites of marine invertebrates. It is still unclear as to whether they are degenerate platyhelminthes or truly-primitive, basal metazoans. Generally, these tiny, elusive creatures consist of a somatoderm of ciliated cells surrounding one or...
.
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, Orthonectida
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:...
, and Rhombozoa
Rhombozoa
Dicyemida, or Rhombozoa, is a phylum of tiny parasites that live in the renal appendages of cephalopods. Although the name "Dicyemida" precedes "Rhombozoa" in usage, and is preferred by most contemporary authors, "Rhombozoa" still enjoys much popular support.Classification is controversial...
. 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.