366 



COLLEGE ZOOLOGY 



RELATIONS OF THE 

 CYCLOSTOMATA TO MAN 



The flesh of the lamprey, in many parts 

 of Europe, has been a popular food for cen- 

 turies. Work has been done in the United 

 States to make lampreys palatable as food, 

 or to find other commercial use for them, 

 but so far these efforts have met with little 

 or no success. Larval lampreys sometimes 

 serve as bait for both commercial and sport 

 fishermen. Some adult lampreys are serious 

 enemies of valuable food and game fishes. 

 The Atlantic lamprey {Petromyzon marinus) 

 is found in all the Great Lakes and now 

 threatens their important commercial fish 

 resources. It passed the Niagara Falls bar- 

 rier by way of the Welland Canal. Lake 

 Huron and Lake Michigan's trout fishing 

 has been practically destroyed by the lam- 

 prey, and Lake Superior's potentiality is 

 30 per cent below that of former years. 

 In 1946, commercial fishermen took a catch 

 of lake trout from Lake Michigan of about 

 5,500,000 pounds but the catch in 1953 

 was only 482 pounds. The lampreys not 

 only kill many fish by feeding on their blood, 

 but they inflict injuries on many leaving 

 scars (Fig. 239) and impairing their com- 

 mercial value. Some large fish show several 

 scars. 



States adjoining the Great Lakes and the 

 United States and Canadian governments 

 are trying to work out methods to control 

 the sea lamprey. At present the electric 

 barriers (weirs) are the most dependable 

 devices in use for sea lamprey control. How- 

 ever, recent experiments with a chemical 

 compound have been reported uncondition- 

 ally successful. Electric weirs, chemical 

 treatment, and other control measures 

 should eventually make the sea lamprey 

 problem less serious. But it is doubtful that 

 this pest will ever be completely removed 

 from the Great Lakes. The St. Lawrence 

 Seaway probably means that the lamprey 

 will always be a troublemaker in the Great 



Lakes, for it doubtless will be brought in 

 from the oceans in increased numbers, at- 

 tached to the bottoms of big ships. 



The migration of the sea lamprey into 

 the Great Lakes is acting as a great disturber 

 of the balance in nature, as is demonstrated 

 by the important influence on the large com- 

 mercial fisheries of these extremely produc- 

 tive waters. 



CLASSIFICATION OF 

 THE LIVING AGNATHA 



(For reference purposes only) 



Class Agnatha includes the orders which 

 constitute the ostracoderms of the Silurian 

 and Devonian geological periods. The ostraco- 

 derms are known only from their fossil remains. 



Order 1. Cyclostomata (the living cyclo- 

 stomes). Hagfishes and lampreys. 

 Eel-shaped; skin smooth, without 

 scales; no lateral fins, functional jaws, 

 or genital ducts; mouth suctorial, 

 with horny teeth; 1 olfactory pit; 7 

 or more pairs of gill clefts. 



The cyclostomes are the most 

 primitive of all living vertebrates. 

 Two suborders are recognized as fol- 

 lows : 

 Suborder 1. Petromyzontia (Gr. petra, 

 rock; myzon, sucker). Lampreys. 

 One family; nasal opening in 

 front of eyes; mouth suctorial; 

 7 pairs of gill slits. Exs. Petromy- 

 zon marinus, sea lamprey (Fig. 

 240), Atlantic Coast from 

 Chesapeake Bay northward, 

 and, in Europe, landlocked in 

 the Finger Lakes; Entosphenus 

 tridentatus, Pacific Coast, south- 

 ern California to Alaska; Ich- 

 thyomyzon, brook lampreys, 

 central North America, includ- 

 ing the Great Lakes; Enfos- 

 phenus lamottenii, nonparasitic 

 lampreys, eastern and midwest- 

 em states. 

 Suborder 2. Myxinoidia (Gr. myxa, 

 slime) . Slime eels and hagfishes. 



