What is Craniata?

For the class of brachiopods, see Craniforma.

Craniata Fossil range: early Early Cambrian - Recent
Pacific Hagfish resting on bottom 280 m down off Oregon coast Pacific Hagfish resting on bottom 280 m down off Oregon coast
Scientific classification
Kingdom: Animalia Phylum: Chordata (unranked) Craniata Janvier 1981
Subphyla
Cephalaspidomorphi (disputed) Myxini Vertebrata

Craniata (sometimes Craniota) is a proposed clade of chordate animals that contains the vertebrates (subphylum Vertebrata) and Myxini (hagfish) as living representatives. Craniata includes all animals with crania (skulls), hence the name.

Craniata as an unranked taxon replaces the former use of Vertebrata (= Vertebrata sensu lato). The main difference of the old and new (= Vertebrata sensu stricto) interpretation of Vertebrata is that Myxini and - usually - the Cephalaspidomorphi too are now not included in Vertebrata anymore. These two taxa lack proper vertebrae, which with the new interpretation are characteristic for vertebrates which they traditionally - and confusingly - were not.(Hickman et al., 2007)

Other characteristics of Craniata include:

• Bipartite heart with atrium and ventricle(s)
• Tripartite brain
• At least one semicircular canal

Systematics and taxonomy

CLADE CRANIATA

• Myxini (= Hyperotreti)
• Myxiniformes
• Myxinidae
• Cephalaspidomorphi
• Vertebrata
• Gnathostomata
• Chondrichthyes
• Teleostomi
• Hyperoartia
• Petromyzontiformes

Validity

The validity of this taxon is in doubt. mtDNA sequence analysis (Delarbre et al 2002) suggests that Myxini are as close to the Hyperoartia (lampreys) as long believed - i.e., that the Agnatha are a valid clade. The Cephalaspidomorphi are traditionally allied with the Hyperoartia, which may or may not be correct. Note however that mtDNA is not very reliable in phylogenetic analysis that reach very deep into time, due to its accelerated rate of mutation, and that the fossil record is quite equivocal.

If the Acrania are indeed not paraphyletic, Vertebrata would return to its old content (Gnathostomata + Agnatha) and Craniata, being superfluous, would become its synonym.

References

• CLEVELAND P. HICKMAN, J., ROBERTS, L. S., KEEN, S. L., LARSON, A. & EISENHOUR, D. J. (2007). Animal Diversity, Fourth Edition. New York: McGraw Hill.2007&rft.pub=McGraw%20Hill&rft.place=New%20York"> 
• Delarbre et al (2002). "Complete Mitochondrial DNA of the Hagfish, Eptatretus burgeri: The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly". Molecular Phylogenetics and Evolution 22 (2): 184-192.