"കോർഡേറ്റ" എന്ന താളിന്റെ പതിപ്പുകൾ തമ്മിലുള്ള വ്യത്യാസം

The phylum Chordata consists of three subphyla: [[Urochordata]], represented by [[tunicate]]s; [[Cephalochordata]], represented by [[lancelet]]s; and [[Craniata]], which includes [[vertebrate|Vertebrata]]. The [[Hemichordata]] have been presented as a fourth chordate subphylum, but they are now usually treated as a separate phylum. Urochordate larvae have both a notochord and a nerve cord which are lost in adulthood. Cephalochordates have a notochord and a nerve cord (but no [[brain]] or specialist sensory organs) and a very simple [[circulatory system]]. Craniates are the only sub-phylum whose members have [[skull]]s. In all craniates except for [[hagfish]], the dorsal hollow nerve cord is surrounded with [[cartilaginous]] or bony vertebrae and the notochord is generally reduced; hence, hagfish are not regarded as vertebrates. The chordates and three sister [[phylum|phyla]], the [[Hemichordata]], the [[Echinodermata]] and the [[Xenoturbellida]], make up the [[deuterostomes]], one of the two [[superphylum|superphyla]] that encompass all fairly complex animals.

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