420 COLLEGE ZOOLOGY 



ently highly specialized. The absence of jaws and of limbs 

 may be due to degeneration. 



Economic Importance. The flesh of the lamprey is used as 

 food both in Europe and America. The number of lampreys, 

 however, has decreased so much within recent years that their 

 value as food is now almost negligible. Fishermen charge the 

 lamprey with destroying numbers of food fishes, which are 

 attacked just beneath the pectoral fins. The flesh is torn with 

 their rasping teeth and the blood sucked out of the body. 



2. CYCLOSTOMATA IN GENERAL 



SUBCLASS I. MYXINOIDEA. THE HAGFISHES. One family, 

 the MYXINID^E, belongs to this subclass. The MYXINID^E are 

 all marine, and are represented by three genera: (i) Bdellostoma 

 (Fig. 352, A) and (2) Paramyxine in the Pacific, and (3) Myxinc 

 (Fig. 352, B) in the Pacific, Atlantic, and North Sea. These 

 hagfishes differ from the lampreys in a number of characters: 

 (i) the nasal aperture is terminal; (2) the pituitary body opens 

 into the pharynx; (3) there are four tentacles on either side of the 

 mouth; (4) the oral sucker is absent, and there is only a single 

 large tooth; (5) there are no neural arches in the trunk, and the 

 branchial basket is poorly developed; and (6) the gills may open 

 by a single common pore on each side (Myxine). 



The hagfishes live in the mud of the sea bottom down to a 

 depth of nearly three hundred and fifty fathoms. They are 

 very destructive to fishes, especially those caught on lines or in 

 nets, boring their way into the body and eating out the soft 

 parts. Cod and flounders are the fish usually attacked. 



SUBCLASS II. PETROMYZONTIA. THE LAMPREYS. The 

 lampreys all resemble Petromyzon in general structure. There 

 is a single family, PETROMYZONTID^:, and a number of genera. 

 Petromyzon inhabits the rivers and seas of America, Europe, 

 and Asia; Lampetra and 1 ' chthyomyzon live in North American 

 streams and lakes; Mordacia and Geotria in South America 

 and Tasmania. 



