The CYCLOSTOMES 



LAMPREYS AND HAGFISHES 



The only true vertebrate parasites are found among the cyclostomes. 

 Some zoologists classify the cyclostomes as fishes; others recognize 

 them as a distinct and diflPerent group, more primitive than fishes 

 and somewhat degenerate. They are eellike forms found in the sea and 

 in fresh water. They contain two important divisions, the hagfishes and 

 the lampreys. The hagfishes are entirely marine. The lampreys are found 

 both in the sea and in fresh water. 



The cyclostomes are all characterized by the absence of several fish 

 characters: paired fins or appendages, true teeth, scales, and upper and 

 lower jaws. They are usually considered very primitive vertebrates in 

 which these structures have not developed. The brain and skull are 

 imperfectly developed. The vertebral column is poorly formed, and 

 most of the supporting structure consists of a stiff, rodlike notochord. 

 The gills open externally through separate gill-clefts. 



Most of the members of this group are carnivorous or semiparasitic. 

 The marine hagfishes are very destructive, for they burrow into the 

 bodies of living fishes and devour their flesh until nothing remains but 

 skin and bones. Many of the lampreys are injurious to fishes. The adults 

 attack fishes with their round, suckerlike mouths. They rasp a hole in 

 the side of the fish and suck blood; when gorged with blood they drop 

 off, leaving terrible round sores, which if they do not actually kill the 

 fish weaken it and frequently cause fatal infections. Fish disfigured by 

 fresh lamprey sores lose their market value. 



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