សត្វឆ្អឹងកង៖ ភាពខុសគ្នារវាងកំណែនានា

 

The vertebrates traditionally include the [[hagfish]], which do not have proper vertebrae, though their closest living relatives, the [[lamprey]]s, do have vertebrae.<ref name=hagfish>{{cite journal|title=Monophyly of Lampreys and Hagfishes Supported by Nuclear DNA–Coded Genes | author=Kuraku et al. |date=December 1999|journal=Journal of Molecular Evolution | volume = 49 | pages = 729–35|doi=10.1007/PL00006595|pmid=10594174|last2=Hoshiyama|first2=D|last3=Katoh|first3=K|last4=Suga|first4=H|last5=Miyata|first5=T|issue=6}}</ref> Hagfish do, however, possess a [[cranium]]. For this reason, the vertebrate subphylum is sometimes referred to as "[[Craniata]]" when discussing morphology. Molecular analysis since 1992 has suggested that the hagfish are most closely related to lampreys,<ref>{{cite journal|last=Stock|first=David|coauthors=Whitt GS|title=Evidence from 18S ribosomal RNA sequences that lampreys and hagfish form a natural group|journal=Science|date=7|year=1992|month=August|volume=257|issue=5071|doi=10.1126/science.1496398|url=http://www.sciencemag.org/content/257/5071/787.short|accessdate=22 November 2011|pages=787–9|pmid=1496398|bibcode = 1992Sci...257..787S }}</ref> and so also are vertebrates in a [[monophyletic]] sense. Others consider them a sister group of vertebrates in the common taxon of Craniata.<ref>{{cite journal|last=Nicholls|first=Henry|title=Mouth to Mouth|date=10 September 2009|journal=Nature|volume=461|issue=7261|pages=164–166|doi=10.1038/461164a|pmid=19741680}}</ref>