CYCLOSTOMATA 413 



nal organs and flesh. They frequently attack living fish which have 

 been otherwise injured. 



Subclass Petromyzontia likewise includes only one family, Petro- 

 myzontidae, which follows the type name. There are several genera 

 including Petromyzon, the common Atlantic form, Ichthyomyzon 

 of the lakes and streams and Entosphenus of the Pacific coast. 

 Entosphenus tridentatus trident atus is the northern form and E. 

 tridcntatus ciliatus is the southern form. The lampreys live in both 

 salt and fresh water, and they are quite predaceous, attacking fish 

 of considerable size. The characteristics of the group will be brought 

 out under the discussion of Lamprey as a typical representative. 



Economic Relations of the Class 



In a general way lampreys are both beneficial and injurious. They 

 all serve as excellent fish food and fish bait when they are in the 

 larval stage. Brook lampreys are classed as wholly beneficial since 

 they feed on microscopic organisms while larvae and do not feed 

 as adults. Sea lampreys and lake lampreys are both valuable as 

 human food, especially just preceding the spawning season. The 

 sea lamprey, for the two or three years it spends in the ocean, lives 

 at the expense of marine fish. It attaches itself and rasps a hole 

 in the side of a fish about once a month, and through the hole thus 

 formed, it sucks the fish's blood. One will remain to a single fish 

 for about five days, get its fill, and release itself. The fish frequently 

 dies as a result. Since the sea lamprey does not feed after it starts 

 up stream, it does little harm to fresh-water fish except as the 

 newly matured ones are making their trip to sea. The lake lamprey 

 is similar except that it spends its entire life in fresh water. They 

 are very destructive to lake fish since they are predaceous and 

 spend their adult lives in the lakes. 



THE LAMPREY 



Habitat 



All live on or in the muddy bottoms of fresh-water streams dur- 

 ing larval stages. In adult life the sea lamprey goes to the open 

 sea and the lake lamprey goes to the deep water of the lakes. Both 

 return to the fresh-water streams to spawn a few years later. 



