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Researchers and taxonomists frequently propose new phyla or eliminate old phyla by joining two together to form a new phylum or by incorporating a smaller phylum into a larger one. Very occasionally a new phylum will be proposed to accommodate a newly discovered organism which does not seem to fit into any current phylum although there is general reluctance to create new phyla and new organisms can often later be fitted into an already existing phylum either on some characteristic not originally noticed or by "expanding" the phylum the new organism is closest to. Such changes are rarely accepted quickly or universally and often generate considerable discussion in the literature. Consequently it is difficult to give an accurate list of phyla or even give a uncontentious count of them.
Researchers and taxonomists frequently propose new phyla or eliminate old phyla by joining two together to form a new phylum or by incorporating a smaller phylum into a larger one. Very occasionally a new phylum will be proposed to accommodate a newly discovered organism which does not seem to fit into any current phylum although there is general reluctance to create new phyla and new organisms can often later be fitted into an already existing phylum either on some characteristic not originally noticed or by "expanding" the phylum the new organism is closest to. Such changes are rarely accepted quickly or universally and often generate considerable discussion in the literature. Consequently it is difficult to give an accurate list of phyla or even give a uncontentious count of them.
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 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; during this time organisms similar to, but not strictly members of, modern phyla existed; 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). The arthropods are still by far the most dominant phylum.
Researchers and taxonomists frequently propose new phyla or eliminate old phyla by joining two together to form a new phylum or by incorporating a smaller phylum into a larger one. Very occasionally a new phylum will be proposed to accommodate a newly discovered organism which does not seem to fit into any current phylum although there is general reluctance to create new phyla and new organisms can often later be fitted into an already existing phylum either on some characteristic not originally noticed or by "expanding" the phylum the new organism is closest to. Such changes are rarely accepted quickly or universally and often generate considerable discussion in the literature. Consequently it is difficult to give an accurate list of phyla or even give a uncontentious count of them.
Valentine, James W. (2004). On the Origin of Phyla. Chicago: University Of Chicago Press. p. 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."
Parker, Andrew (2003). In the blink of an eye: How vision kick-started the big bang of evolution. Sydney: Free Press. pp. 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."
"…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" (URL accessed on July 5, 2006)
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"