CLASS AGNATHA 



365 



Figure 243. American brook lampreys spawning. (Courtesy of Institute for Fisheries Research, 

 Michigan Department of Conservation.) 



place. It is at this stage that the parasitic 

 species begins to feed on fish. 



BROOK LAMPREY 



The nonparasitic brook lampreys of North 

 America, Entosphenus lamottenii, breed in 

 the spring. They move stones by means of 

 their oral hoods until a space is cleared on 

 the bottom where a number of them may 

 congregate. A male clings to the head of a 

 female for a moment, winds his tail about 

 her body, and discharges spermatozoa over 

 the eggs when they are extruded. There is 

 a long larval stage in development. After 

 spawning the adults probably take no food 

 and soon die; they are therefore not injuri- 

 ous to fishes. 



HAGFISHES 



Hagfishes live in the mud of the sea bot- 

 tom, down to a depth of nearly 350 fathoms. 

 They are very destructive to fishes, especially 



those caught on lines or in nets; they bore 

 their way into the body and eat out the 

 soft parts. Cod and flounders are the fish 

 usually attacked. 



In the hagfishes the same individual pro- 

 duces first sperms and then later eggs. 

 Growth to the adult is direct, that is, with- 

 out a larval stage. 



RELATIONS OF THE 



CYCLOSTOMATA TO 



OTHER GROUPS 



The chordate characters of the cyclo- 

 stomes are obvious. Some, such as a continu- 

 ous notochord and many gill slits, are simi- 

 lar to the primitive characters of the 

 amphioxus. Others are of a more advanced 

 nature, such as a distinct head, cranium, 

 better-developed brain, and cartilaginous 

 neural arches. Cyclostomcs are less advanced 

 than fishes as indicated by the absence of 

 hinged jaws, paired limbs, true teeth, and 

 complete vertebrae. 



