   #copyright

Chordate

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

   iChordates

                   Fossil range: Latest Ediacaran - Recent

   Yellowfin tuna, Thunnus albacares
   Yellowfin tuna, Thunnus albacares
                 Scientific classification

   Domain:      Eukaryota
   Kingdom:     Animalia
   Subkingdom:  Eumetazoa
   (unranked)   Bilateria
   Superphylum: Deuterostomia
   Phylum:      Chordata
                Bateson, 1885

                               Typical Classes

   See below

   Chordates ( phylum Chordata) are a group of animals that includes the
   vertebrates, together with several closely related invertebrates. They
   are united by having, at some time in their life, a notochord, a hollow
   dorsal nerve cord, pharyngeal slits, an endostyle, and a muscular tail
   extending past the anus. Some scientists argue that the true qualifier
   should be pharyngeal pouches rather than slits.

   The phylum Chordata is broken down into three subphyla: Urochordata,
   Cephalochordata, and Vertebrata. Urochordate larvae have a notochord
   and a nerve cord but they are lost in adulthood. Cephalochordates have
   a notochord and a nerve cord but no vertebrae. In all vertebrates
   except for Hagfish, the dorsal hollow nerve cord has been surrounded
   with cartilaginous or bony vertebrae and the notochord generally
   reduced.

   The chordates and two sister phyla, the hemichordates and the
   echinoderms, make up the deuterostomes, a superphylum.

   The extant groups of chordates are related as shown in the phylogenetic
   tree below. Many of the taxa listed do not match traditional classes
   because several of those classes are paraphyletic. Different attempts
   to organize the profusion of chordate clades into a small number of
   groups, some with and some without paraphyletic taxa, have thrown
   vertebrate classification is in a state of flux. Also, the
   relationships of some chordate groups are not very well understood.

Classes of Chordata

   In the subphylum Urochordata classes Ascidiacea, Thaliacea, Larvacea
   are found. Includes the sea squirts and tunicates.

   In subphylum Cephalochordata, the worm-like lancelets are found.

   In the subphylum Vertebrata (all animals with vertebrae) classes Myxini
   (hagfish), Conodonta, Hyperoartia (lampreys), Cephalaspidomorphi,
   Pteraspidomorphi, Placodermi, Chondrichthyes (sharks, rays and skates),
   Acanthodii (spiny sharks), Actinopterygii (ray-finned fish),
   Sarcopterygii (lobe-finned fish), Amphibia (amphibians), Sauropsida
   (reptiles), Synapsida, Aves (birds), and Mammalia (mammals) are found.

Classification

Taxonomy

     * Phylum Chordata
          + Subphylum Urochordata - Tunicates
          + Subphylum Cephalochordata - Lancelets
          + Class Myxini or Hyperotreti ( hagfish)
          + Subphylum Vertebrata (Vertebrates - animals with backbones)
               o Class Conodonta (Conodonts)
               o Class Cephalaspidomorphi (jawless fish)
               o Class Pteraspidomorphi (Paleozoic jawless fish)
               o Infraphylum Gnathostomata ( jawed vertebrates)
                    # Class Placodermi (Paleozoic armoured forms)
                    # Class Chondrichthyes (cartilaginous fish)
                    # Class Acanthodii (Paleozoic "spiny sharks")
                    # Superclass Osteichthyes (bony fishes)
                         @ Class Actinopterygii (ray-finned fish)
                         @ Class Sarcopterygii (lobe-finned fish)
                         @ Superclass Tetrapoda (four-legged vertebrates)
                              - Class Amphibia (amphibians)
                              - Series Amniota (amniotic egg)
                                   = Class Synapsida (mammal-like
                                     "reptiles")
                                   = Class Mammalia (mammals)
                                   = Class Sauropsida - (reptiles)
                                   = Class Aves (birds)

Phylogeny

Chordata
├─ Urochordata ( tunicates)
├─ Cephalochordata ( lancelets)
└ Craniata (animals with skulls)
     ├─ Myxini or  Hyperotreti ( hagfish)
     └ Vertebrata (animals with backbones)
        ├─ Conodonta (Conodonts)
        ├─ Cephalaspidomorphi (Paleozoic jawless fish)
        ├─ Hyperoartia ( lampreys and kin)
        ├─ Pteraspidomorphi (other Paleozoic jawless fish)
        └ Gnathostomata ( jawed vertebrates)
             ├─ Placodermi (Paleozoic armoured forms)
             ├─ Chondrichthyes (cartilaginous fish)
             └ Teleostomi (advanced fishes and their descendants)
                    ├─ Acanthodii (Paleozoic "spiny sharks")
                    └─ Osteichthyes (bony fishes)
                            ├─ Actinopterygii (ray-finned fish)
                            └─ Sarcopterygii (lobe-finned fish)
                                     └ Tetrapoda (four-legged vertebrates)
                                             ├─ Lissamphibia (frogs and kin)
                                             └ Amniota (amniotic egg)
                                                  ├ Synapsida (mammals and kin)
                                                  └Sauropsida (reptiles and bird
s)

   Note: Lines show probable evolutionary relationships (including extinct
   members of taxa)

   Retrieved from " http://en.wikipedia.org/wiki/Chordate"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
