Metazoa

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Related to Metazoans: Eumetazoans

Metazoa

(mĕt'əzō`ə), subkingdom of the animal kingdom comprising the multicellular animals in the traditional two-kingdom system of taxonomic classification, in which living organisms were considered to be either plants or animals. Metazoa included all animals except the protozoans, formerly classified as in the phylum Protozoa but now classified in the kingdom ProtistaProtista
or Protoctista
, in the five-kingdom system of classification, a kingdom comprising a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms.
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. The term is still used informally.

Metazoa

The kingdom (or subkingdom) comprising all many-celled animals, whether constructed of simple tissue layers or of complex organs. In some five-kingdom systems and in the six-kingdom systems of classification for living organisms, metazoans constitute a separate kingdom, while in the older two-kingdom and some three-kingdom systems the subphylum Metazoa made up the greater part of the kingdom Animalia. Most usual classifications subdivide the Metazoa into about 30 phyla of many-celled animals (such as Arthropoda or Mollusca), each representing a major kind of body design. In all classifications, the only animal forms not included in the Metazoa are the single-celled protozoa (Protista) and the independently evolved sponges (Parazoa). See Animal kingdom, Eukaryotae, Porifera, Protista

Metazoans are made up of eukaryotic cells, each with a membrane surrounding the nuclear material and with the mechanics of cell multiplication always involving the mitotic division of chromosomes. Cellular specialization is common. In addition to increasing functional interdependence and specialization of cells, the evolution of the higher phyla of Metazoa has involved the potentialities and penalties of increasing size, particularly those associated with the surface-mass ratio. Despite differing grades of structural and functional complexity, interdependence of organs, tissues, and cell types is diagnostic of the phyla of animals making up the kingdom (or subkingdom) Metazoa. See Classification, biological, Homeostasis

Metazoa

[‚med·ə′zō·ə]
(zoology)
The multicellular animals that make up the major portion of the animal kingdom; cells are organized in layers or groups as specialized tissues or organ systems.
References in periodicals archive ?
Two approaches were utilized to mine transcriptomic data from 179 metazoan species and 2 choanoflagellate species for putative Hc genes in silico (Table A1).
"The contrasting findings by different research groups should stimulate interest and more research dedicated to understanding the curious physiologies of metazoans in DHABs."
Stromatoporoids, corals and bryozoans became the major contributors to metazoan reefs.
(23) The earliest fossils of metazoans (multi-celled animals) may be represented by simple disk-shaped fossils found in rocks 610-600 million years old.
The acritarchs are uniformly small (< 10 [micro]m diameter), which suggests that they represent primary productivity ('algal' cysts) rather than (for example) the egg cases of metazoans, and so the pellets can be assigned to an herbivorous metazoan grazer, and possibly a member of the zooplankton.
During apoptosis in metazoans, caspases cleave PARP [Poly (ADP-ribose) polymerase], a DNA repair enzyme.
Why are they still classified as metazoans? Is it true that they haven't evolved in millions of years?