Back لافكيات Arabic لافكيات ARZ Agnatha AST Çənəsizlər Azerbaijani چنهسیزلر AZB Бяссківічныя Byelorussian Бяссківічныя BE-X-OLD Безчелюстни Bulgarian Àgnats Catalan Agnatha CEB
| Agnathan Temporal range: Cambrian – Recent
| |
|---|---|
| |
| Lampetra fluviatilis | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Subphylum: | |
| Superclass: | Agnatha Cope, 1889
|
The Agnatha is a superclass of fish. It is paraphyletic. This means it is a convenient catch-all term, which does not follow the rules of cladistics.
For example, most extinct agnathans belong to the stem group (ancestral group) of gnathostomes.[1][2] But according to the rules, one sister group should not contain ancestors of another sister group.
The living Agnatha (lampreys and hagfish) are known as cyclostomes. Recent molecular data from rRNA,[3] and from mtDNA,[4] show that these living agnathans are monophyletic. There are about 100 species. Hagfish are vertebrates but do not have vertebrae. It is believed that they lost their vertebrae during their lifestyle adaptations.
The lifestyle of the lamprey (an ectoparasite on other fish) and hagfish (a scavenger) means that they are not typical of the fossil groups, which were free-swimming and often armoured.
- ↑ Zhao Wen-Jin & Zhu Min 2007. Diversification and faunal shift of Siluro-Devonian vertebrates of China. Geological Journal 42, 351–369. [1]
- ↑ Sansom, Robert S. 2009. Phylogeny, classification & character polarity of the Osteostraci (Vertebrata). Journal of Systematic Palaeontology 7: 95–115. [2]
- ↑ Mallatt J. & Sullivan J. 1998. 28S and 18S ribosomal DNA sequences support the monophyly of lampreys and hagfishes. Molecular Biology and Evolution 15 (12): 1706–1718. [3]
- ↑ DeLarbre, Christiane 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. [4]