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A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə).All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa.
This article contains a list of all of the classes and orders that are located in the Phylum Chordata. The subphyla Tunicata and Vertebrata are in the unranked Olfactores clade, while the subphylum Cephalochordata is not. Animals in Olfactores are characterized as having a more advanced olfactory system than animals not in it.
Appendicularia retains the ancestral chordate characteristics of having the pharyngeal spiracles and the anus open directly to the outside, and by the lack of the atrium and the atrial siphon found in related classes. The gonads are located in the posterior section of the trunk, beyond the digestive tract.
Mammalia is a class of animal within the phylum Chordata. Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums. [1]
According to this theory, there is a deep agreement between the vertebrates and cephalochordates, and even all chordates. [75] [76] With the advent of molecular genetics lancelets are once again regarded as a model of vertebrate ancestors, and are used again as a model organism. [77] [30]
A third class, the Larvacea (or Appendicularia), is the only group of tunicates to retain their chordate characteristics in the adult state, a product of extensive neoteny. The 70 species of larvaceans superficially resemble the tadpole larvae of amphibians, although the tail is at right angles to the body.
A craniate is a member of the Craniata (sometimes called the Craniota), a proposed clade of chordate animals with a skull of hard bone or cartilage.Living representatives are the Myxini (hagfishes), Hyperoartia (including lampreys), and the much more numerous Gnathostomata (jawed vertebrates).
The Cambrian chordates are an extinct group of animals belonging to the phylum Chordata that lived during the Cambrian, between 538 and 485 million years ago. The first Cambrian chordate known is Pikaia gracilens , a lancelet -like animal from the Burgess Shale in British Columbia , Canada.