Editing Hagfish (section)

==Classification==
[[File:Pacific_hagfish_Myxine.jpg|thumb|[[Pacific hagfish]] resting on the ocean bottom, at 280&nbsp;m depth off the [[Oregon]] coast]]
Originally, ''Myxine'' was included by [[Linnaeus]] ([[10th edition of Systema Naturae|1758]]) in [[Vermes]]. The fossil hagfish ''[[Myxinikela|Myxinikela siroka]]'', from the Late Carboniferous of the United States, is the oldest-known member of the group. It is in some respects more similar to lampreys, but shows key [[autapomorphies]] of hagfish.<ref name=":3">{{Cite journal|last=Miyashita|first=Tetsuto|date=23 November 2020|title=A Paleozoic stem hagfish Myxinikela siroka — revised anatomy and implications for evolution of the living jawless vertebrate lineages|url=https://www.researchgate.net/publication/346740531|journal=Canadian Journal of Zoology|language=en|volume=98|issue=12|pages=850–865|doi=10.1139/cjz-2020-0046|s2cid=229489559|issn=0008-4301}}</ref> In recent years, hagfish have become of special interest for genetic analysis investigating the relationships among [[chordate]]s. Their classification as [[agnatha]]ns places hagfish as elementary [[vertebrate]]s in between [[invertebrate]]s and [[gnathostome]]s. However, discussion has long occurred in scientific literature about whether the hagfish were even [[invertebrate]]. Using fossil data, paleontologists posited that lampreys are more closely related to gnathostomes than hagfish. The term "Craniata" was used to refer to animals that had a developed skull, but were not considered true vertebrates.<ref>{{cite journal| year=1993 |last1=Forey|first1=P.| last2=Janvier | first2 = P. | title = Agnathans and the origin of jawed vertebrates|journal =Nature | volume = 361|issue=6408 |pages=129–134| doi = 10.1038/361129a0|bibcode=1993Natur.361..129F|s2cid=43389789}}</ref> Molecular evidence in the early 1990s first began suggesting that lampreys and hagfish were more closely related to each other than to gnathostomes.<ref>{{cite journal| year=1992 |last1=Stock|first1=D.W.| last2=Whitt| first2 = G.S. | title = Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group. |journal =Science | volume = 257|issue=5071 |pages=787–9| doi = 10.1126/science.1496398 |pmid=1496398|bibcode=1992Sci...257..787S}}</ref> The validity of the taxon "Craniata" was further examined by Delarbre et al. (2002) using [[mtDNA]] [[DNA sequence|sequence]] data, concluding the Myxini are more closely related to the [[Hyperoartia]] than to the Gnathostomata—i.e., that modern jawless fishes form a clade called the [[Cyclostomata]]. The argument is that if the Cyclostomata are indeed monophyletic, Vertebrata would return to its old content ([[Gnathostomata]] + Cyclostomata) and the name Craniata, being superfluous, would become a junior synonym.<ref name="r3">{{cite journal |author=Janvier, P. |author-link=Philippe Janvier |year=2010 |title=MicroRNAs revive old views about jawless vertebrate divergence and evolution |journal=Proceedings of the National Academy of Sciences |volume=107 |issue=45 |pages=19137–19138 |bibcode=2010PNAS..10719137J |doi=10.1073/pnas.1014583107 |pmc=2984170 |pmid=21041649 |quote=Although I was among the early supporters of vertebrate paraphyly, I am impressed by the evidence provided by Heimberg et al. and prepared to admit that cyclostomes are, in fact, monophyletic. The consequence is that they may tell us little, if anything, about the dawn of vertebrate evolution, except that the intuitions of 19th century zoologists were correct in assuming that these odd vertebrates (notably, hagfishes) are strongly degenerate and have lost many characters over time |doi-access=free}}</ref> Nowadays, molecular data are almost unanimously in consensus of cyclostome monophyly, with more recent work being directed at shared microRNAs between cyclostomes and gnathostomes.<ref>{{cite journal| year=2010 |last1=Heimberg|first1=A.M| last2=Cowper-Sal| first2 = R | last3 = Semon | first3 = M | last4 = Donoghue | first4 = P.C | last5 = Peterson | first5 = K.J | display-authors = 1 | title = microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate. |journal =Proceedings of the National Academy of Sciences| volume = 107|issue=45 |pages=19379–83|doi=10.1073/pnas.1010350107|pmid=20959416|pmc=2984222|doi-access=free}}</ref> The current classification supported by molecular analyses (which show that lampreys and hagfishes are sister taxa), as well as the fact that hagfishes do, in fact, have rudimentary vertebrae, which places hagfishes in Cyclostomata.<ref name=":0"/>