Agnatha (Lampreys, Hagfishes, Ostracoderms)

Abstract

Agnathans are an ensemble of jawless (non‐gnathostome) vertebrates, some of which are more closely related to the gnathostomes than others. Living agnathans fall into two groups, hagfishes (Hyperotreta) and lampreys (Hyperoartia), united into a higher group, the cyclostomes (Cyclostomi).

Keywords: hyperotreta; hyperoartia; cyclostomes; vertebrates; gnathostomes

Figure 1.

Living agnathans. (a) Hagfishes; top, the Pacific hagfish Eptatretus in lateral view; bottom; the head skeleton of the Atlantic hagfish Myxine. (b) Lampreys; top, the brook lamprey Lampetra in lateral view; bottom, the head skeleton of the brook lamprey.

Figure 2.

Attempted reconstructions of fossil agnathans. (a) Haikouichthys, Lower Cambrian of China; (b) the hagfish Myxinikela, Carboniferous of USA; (c) the lamprey Mayomyzon, Carboniferous of USA; (d) the anaspid Rhyncholepis, Silurian of Norway; (e) the thelodont Loganellia, Silurian of Scotland; (f) the arandaspid Sacabambaspis, Ordovician of Bolivia; (g) the heterostracan Tartuosteus, Middle Devonian of Estonia; (h) the heterostracan Poraspis, Lower Devonian of Spitsbergen; (i) the pituriaspid Pituriaspis, Middle Devonian of Australia; (j) the osteostracan Zenaspis, Lower Devonian of Scotland; (k) the galeaspid Polybranchiaspis, Lower Devonian of China; (l) the euconodont Clydagnathus, Carboniferous of Scotland. The sizes of the fish range from about 3–4 cm (a,l) to 1 m (g) in length.

Figure 3.

Interrelationships and distribution of the vertebrates in time.

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Further Reading

Aldridge RJ, Briggs DEG, Smith MP, Clarkson ENK and Clark NDL (1993) The anatomy of conodonts. Philosophical Transactions of the Royal Society of London series B – Biological Sciences 340: 405–421.

Bardack D (1991) First fossil hagfish (Myxinoidea): a record from the Pennsylvanian of Illinois. Science 254: 701–703.

Bardack D and Zangerl R (1971) Lampreys in the fossil record. In: Hardisty MW and Potter IC (eds) The Biology of Lampreys, vol. 1, pp. 67–84. London, Academic Press.

Hardisty MW and Potter IC (eds) (1974–1982) The Biology of Lampreys. London, Academic Press.

Janvier P (1993) Patterns of diversity in the skull of jawless fishes. In: Hanken M and Hall BK (eds) The Skull, pp. 131–188. Chicago: University of Chicago Press.

Janvier P (1996) Early Vertebrates. Oxford: Oxford University Press.

Janvier P (1996) The dawn of the vertebrates: characters versus common ascent in the rise of current vertebrate phylogenies. Palaeontology 39: 259–287.

Jørgensen JM, Lomholt JP, Weber RE and Malte H (eds) (1998) Biology of Hagfishes. London: Chapman & Hall.

Løvtrup S (1977) The Phylogeny of Vertebrata. New York: Wiley.

Stock DW and Whitt GS (1992) Evidence from 18S ribosomal RNA that lampreys and hagfishes form a natural group. Science 257: 787–789

Yalden DW (1985) Feeding mechanisms as evidence for cyclostome monophyly. Zoological Journal of the Linnean Society 84: 291–300.

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How to Cite close
Janvier, Philippe(Apr 2001) Agnatha (Lampreys, Hagfishes, Ostracoderms). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001532]