Phylum

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The hierarchy of biological classification's major eight taxonomic ranks. A kingdom contains one or more phyla. Intermediate minor rankings are not shown.

In biological taxonomy, a 'phylum' plural: Φῦλα phyla) is a taxonomic rank at the level below Kingdom and above Class. "Phylum" is adopted from the Greek φυλαί phylai, the clan-based voting groups in Greek city-states. Phyla represent the largest generally accepted groupings of animals and other living things with certain evolutionary traits, although the phyla themselves may sometimes be grouped into superphyla (e.g. Ecdysozoa with eight phyla, including arthropods and roundworms; and Deuterostomia with the echinoderms, chordates, hemichordates and xenoturbellae). Informally, phyla can be thought of as grouping animals based on general body plan;^[1] this is morphological grouping. Thus despite the seemingly different external appearances of organisms, they are classified into phyla based on their internal organizations.^[2] For example, though seemingly divergent, spiders and crabs both belong to Arthropoda, whereas earthworms and tapeworms, similar in shape, are from Annelida and Platyhelminthes, respectively. Although the International Code of Botanical Nomenclature allows the use of the term "Phylum" in reference to plants, the term "Division" is almost always used by botanists.

The best known animal phyla are the Mollusca, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Echinodermata, and Chordata, the phylum to which humans belong. Although there are approximately 35 phyla, these nine include the majority of the species. Many phyla are exclusively marine, and only one phylum is entirely absent from the world's oceans: the Onychophora or velvet worms. The most recently discovered phylum is Cycliophora^[3] found in 1993; only three phyla were discovered in the last century.

The Cambrian explosion was a great flowering of life forms that occurred between roughly 530 and 520 million years ago;^[4] during this time organisms similar to, but not strictly members of, modern phyla existed;^[5] whilst some appear to be represented in the Ediacaran biota, it remains a matter of debate whether all phyla existed prior to the explosion. Over time the roles among different phyla have varied. For instance, during the Cambrian, the dominant megafauna, or large animals, were arthropods, whereas now the megafauna is dominated by vertebrates (chordata).^[6] The arthropods are still by far the most dominant phylum.

[edit] List of animal phyla

[edit] Groups formerly ranked as phyla

[edit] List of plant divisions

[edit] List of fungi divisions

[edit] See also

• Cladistics
• Phylogenetics
• Systematics
• Taxonomy

[edit] References

1. ^ Valentine, James W. (2004). On the Origin of Phyla. Chicago: University Of Chicago Press, 7. 0226845486. "Classifications of organisms in hierarchical systems were in use by the seventeenth and eighteenth centuries. usually organisms were grouped according to their morphological similarities as perceived by those early workers, and those groups were then grouped according to their similarities, and so on, to form a hierarchy."
2. ^ Parker, Andrew (2003). In the blink of an eye: How vision kick-started the big bang of evolution. Sydney: Free Press, 1–4. 0743257332. "The job of an evolutionary biologist is to make sense of the conflicting diversity of form – there is not always a relationship between internal and external parts. Early in the history of the subject, it became obvious that internal organisations were generally more important to the higher classification of animals than are external shapes. The internal organisation puts general restrictions on how an animal can exchange gases, obtain nutrients and reproduce."
3. ^ "…when a new animal species is discovered, no matter how unusual, it can normally be classified into a known group of creatures with the same body plan or phylum. Although there are 1.5 million plus known species in the world, they can all be classified into 35 or so phyla. These include the chordates (eg the vertebrates such as man), molluscs (snails) and arthropods (jointed limbed e.g. insects). However, S.pandora was so unusual that it could not be classified into any of the existing phyla, and a new one was suggested called Cycliophora" [1] (URL accessed on July 5, 2006)
4. ^ Valentine, J.W.; Jablonski, D.; Erwin, D.H. (1999-03-01). "Fossils, molecules and embryos: new perspectives on the Cambrian explosion". Development 126: 851–859. 
5. ^ Budd, G.E.; Jensen, S. (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews 75 (02): 253–295. doi:10.1017/S000632310000548X. 
6. ^ "The Cambrian Explosion … The organisms range from the prokaryotic cyanobacteria to eukaryotic green and red algae, to sponges, brachiopods, priapulids, annelids, and many different arthropod groups, as well as echinoderms and possibly one of the first chordates." [2] (URL accessed on July 5, 2006)
7. ^ Feldkamp, S. (2002) Modern Biology. Holt, Rinehart, and Winston, USA. (pp. 725)
8. ^ Species Register. Flatworms — Phylum Platyhelminthes. Marine Discovery Centres. Retrieved on 2007-04-09.
9. ^ "Kingdon Plantae Tree of Life"

[edit] External links

• Major Phyla Of Animals
• Are phyla "real"? Is there really a well-defined "number of animal phyla" extant and in the fossil record?

Etymology:

• American Heritage Dictionary: New Latin phylum, from Greek phūlon, class.
• Online Etymological Dictionary: from Gk. phylon "race, stock," related to phyle "tribe, clan," and phylein "bring forth" of physikos "pertaining to nature," from physis "nature"

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