Editing Craniate (section)

==Characteristics==
In the simplest sense, craniates are chordates with well-defined heads, thus excluding members of the chordate subphyla [[Tunicata]] (tunicates) and [[Cephalochordata]] (lancelets), but including [[Myxini]], which have cartilaginous crania and tooth-like structures composed of [[keratin]]. Craniata also includes all [[Cephalaspidomorphi|lampreys and armoured jawless fishes]], [[Placodermi|armoured jawed fish]], [[Chondrichthyes|sharks, skates, and rays]], and [[Teleostomi|teleostomians:]] [[Acanthodii|spiny sharks]], [[Osteichthyes|bony fish]], [[lissamphibia]]ns, [[Temnospondyli|temnospondyls]] and [[Parareptiles|protoreptiles]], [[sauropsids]] and [[mammal]]s. The craniate head consists of a three-part [[brain]], [[neural crest]] which gives rise to many cell lineages, and a cranium.<ref>Campbell & Reece 2005 pp. 675–7</ref><ref>Parker & Haswell 1921</ref>

In addition to distinct crania (sing. ''[[cranium]]''), craniates possess many derived characteristics, which have allowed for more complexity to follow. [[Molecular biology|Molecular-genetic]] analysis of craniates reveals that, compared to less complex animals, they developed duplicate sets of many [[gene]] families that are involved in [[cell signaling]], [[Transcription (genetics)|transcription]], and [[morphogenesis]] (see [[homeobox]]).<ref name="Campbell & Reece 2005 p. 676" />

In general, craniates are much more active than tunicates and lancelets and, as a result, have greater metabolic demands, as well as several anatomical adaptations. Aquatic craniates have gill slits, which are connected to muscles to pump water through the slits, engaging in both feeding and gas exchange (as opposed to lancelets, whose [[pharyngeal slit]]s are used only for suspension feeding, chiefly by cilia-mucus rather than muscles). Muscles line the alimentary canal, [[Peristalsis|moving]] food through the canal, allowing higher craniates such as mammals to develop more complex digestive systems for optimal food processing. Craniates have cardiovascular systems that include a heart with at least two chambers, [[red blood cells]], oxygen transporting [[hemoglobin]] as well as [[myoglobin]], [[liver]]s and [[kidney]]s.<ref name="Campbell & Reece 2005 p. 676" />