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In biological taxonomy, a 'phylum' plural: Φῦλα phyla) is a taxonomic rank at the level below Class and above Kingdom. "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 arrow worms). 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.

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.

List of animal phylaEdit

Phylum Meaning Group Distinguishing characteristics

Species described
Acanthocephala Thorny head Thorny-headed worms Reversible spiny proboscis about 750
Acoelomorpha Without gut Acoels No mouth or alimentary canal
Annelida Little ring Segmented worms Multiple circular segments about 15,300 modern
Arthropoda Jointed foot Arthropods Chitin exoskeleton 1,134,000+
Brachiopoda Arm foot Lamp shells Lophophore and pedicle between 300 and 500 extant
Bryozoa Moss animals Moss animals, sea mats Lophophore, no pedicle, ciliated tentacles about 5,000 living species
Chaetognatha Longhair jaw Arrow worms Chitinous spines either side of head, fins about 100 modern species
Chordata Cord Chordates Hollow dorsal nervous chord about 100,000+
Cnidaria Stinging nettle Coelenterates Nematocysts (stinging cells) about 11,000
Ctenophora Comb bearer Comb jellies Eight "comb rows" of fused cilia about 100 modern species
Cycliophora Wheel carrying Symbion Circular mouth surrounded by small cilia at least 3
Echinodermata Spiny skin Echinoderms Five-fold radial symmetry, mesodermal calcified spines about 7,000 living species and 13,000 extinct ones
Echiura Spine tail Spoon worms Set of hooks at posterior end about 140
Entoprocta Inside anus Goblet worm Anus inside ring of cilia about 150
Gastrotricha Hair stomach Meiofauna Two terminal adhesive tubes about 690
Gnathostomulida Jaw orifice Jaw worms about 100
Hemichordata Half cord Acorn worms Stomochord in collar about 100 living species
Kinorhyncha Motion snout Mud dragons Eleven segments, each with a dorsal plate about 150
Loricifera Corset bearer Brush heads Umbrella-like scales at each end about 122
Mesozoa Middle animals Mesozoans Somatoderm of ciliated cells surrounding reproductive cell(s)
Micrognathozoa Tiny jaw animals Accordion like extensible thorax 1
Mollusca Thin shell Mollusks / molluscs Muscular foot and mantle round shell 112,000[7]
Myxozoa Slime animals Polar capsules resembling nematocysts 13,000+
Nematoda Thread like Round worms Round cross section, keratin cuticle 80 000 – 1 million
Nematomorpha Thread form Horsehair worms about 320
Nemertea A sea nymph Ribbon worms about 1200
Onychophora Claw bearer Velvet worms Legs tipped by chitinous claws about 200 modern
Orthonectida Straight swim about 20
Phoronida Zeus' mistress Horseshoe worms U-shaped gut 20
Placozoa Plate animals 1
Platyhelminthes Flat worms Flat worms about 25,000[8]
Porifera Pore bearer Sponges Perforated interior wall over 5,000 modern
Priapulida Penis Priapulid worms Retractable proboscis surrounded by papillae 17
Rhombozoa Lozenge animal Single axial cell surrounded by ciliated cells 75
Rotifera Wheel bearer Rotifers Anterior crown of cilia about 2000
Sipuncula Small tube Peanut worms Mouth surrounded by invertible tentacles 144–320
Tardigrada Slow step Water bears Four segmented body and head 1,000+
Xenoturbellida Strange flatworm Ciliated deuterostome 2
TOTAL 2,000,000-

Groups formerly ranked as phylaEdit

Name as phylum Common name Current consensus
Craniata Subgroup of phylum Chordata; perhaps synonymous with Vertebrata.
Cephalochordata Lancelets Subphylum of phylum Chordata
Cephalorhyncha Superphylum Scalidophora.
Enterepneusta Acorn worms Class of phylum Hemichordata.
Pentastomida Tongue worms Subclass of Maxillopoda of phylum Arthropoda.
Pogonophora Beard worms Part of family Siboglinidae of phylum Annelida.
Pterobranchia Class of phylum Hemichordata.
Symplasma Glass sponges Class Hexactinellida of phylum Porifera.
Urochordata Tunicates Subphylum of phylum Chordata.
Vestimentifera Vent worms Part of family Siboglinidae of phylum Annelida.


See alsoEdit

References Edit

  1. Valentine, James W. (2004). On the Or35946549igin of Phyla, 7, Chicago: University Of Chicago Press. 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, 1–4, Sydney: Free Press. 074325733254530146."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,54651634Insert non-formatted text here 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 nutr6465468787ients 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.
  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. URL accessed on 2007-04-09.

External linksEdit

Etymology:

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