CHAPTER XV 

 SUBPHYLUM VERTEBRATA: CLASS I. CYCLOSTOMATA 



THE CYCLOSTOMATA (Fig. 352) are vertebrates that have a 

 superficial resemblance to eels, but differ from them as well as 

 from all other vertebrates in many important respects. They 

 are without functional jaws and lateral appendages, and have 



FIG. 352. CYCLOSTOMES. A, Bdellostoma dombeyi. Light apertures along 

 side are mucous pits; dark apertures are branchial openings. B, Myxiitr 

 tfutinosa. Left common branchial aperture is at *. C, Petromyzon m-ariim* 

 (From Dean.) 



only one olfactory pit. Cyclostomes are commonly known as 

 hags and lampreys. There are two subclasses, the MYXINOIDEA 

 or hagfishes, and the PETROMYZONTIA or lampreys; the former 

 are all marine; the latter are found both in salt water and fresh 

 water. They usually feed on the mucus, blood, and even the 

 internal organs of fishes, which they attack with their rasping 

 mouth, 



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