AGNATHAN

any of the class Agnatha of primitive, jawless fishes that includes the lampreys and hagfishes (order Cyclostomata), as well as extinct groups. Hagfishes are minor pests of commercial food fisheries of the North Atlantic, but because of their parasitic habit, lampreys have been a serious pest of food fisheries in the Great Lakes in North America, where they have reduced the numbers of lake trout and other species. Agnathans are otherwise of little economic importance. The group is of great evolutionary interest, however, because it includes the oldest known craniate fossils and because the living agnathans have many primitive characteristics. Additional reading V.C. Applegate, Natural History of the Sea Lamprey, Petromyzon marinus, in Michigan, Spec. Scient. Rep. U.S. Fish Wildl. Serv. 55 (1950), an account of lamprey life history and the pest problem; A. Brodal and R. Fange (eds.), The Biology of Myxine (1963), an authoritative work by 24 authors; M. Fontaine, Formes actuelles de cyclostomes, in P.P. Grass (ed.), Trait de zoologie, vol. 13, pp. 1172 (1958), the best general account of cyclostomes (well illustrated); M.W. Hardisty and I.C. Potter (eds.), The Biology of Lampreys (1972), a comprehensive reference; A.J. Marshall, Agnatha, in T.J. Parker and W.A. Haswell, Textbook of Zoology, 7th ed., vol. 1 (1962), a good account of comparative anatomy, written for university students; E. Stensio, Les Cyclostomes fossiles ou ostracodermes, in J. Piveteau (ed.), Trait de palontologie, vol. 4, pp. 96382 (1964); R. Strahan, The Behaviour of Myxinoids, Acta Zool. Stockh., 44:73102 (1963).