24 



VERTEBRATE ANIMALS OF THE UNITED STATES 



Subclass I. Cyclostomata. — Fish-like vertebrates with a cylin- 

 drical, eel-like body, without scales, paired fins, gill-arches or jaws; 

 skeleton cartilaginous and without ribs; skull imperfectly developed 

 and not separate from the vertebral column; nostril single, median; 

 mouth suctorial; gills sac-like, 6 to 14 in number, opening to the out- 

 side through paired pores; no genital ducts, sympathetic nervous 

 system, arterial bulb, pancreas, spleen or air bladder; median fins on 

 posterior half of body: about 20 species, mostly parasitic on fishes in 

 both fresh and salt water, grouped in 2 orders. The first of these orders, 

 with 2 American species, the Californian hagfish, Polistotrema stouti 

 (Lockington) and the Atlantic hagfish, Myxine glutinosa L., is exclu- 

 sively marine. 



Key to the Orders of Cyclostomata 



ai Gill openings not near head; hagfish, all marine, and not included 



in this book i. Hyperoireta. 



aj Gill openings immediately back of head; lampreys 2. Hyperoartia. 



Order 2. Hyperoartia. — The lampreys. Body cylindrical ante- 

 riorly, compressed posteriorly; fins median and well developed, the 



dorsal fin being more or less completely sepa- 

 rated by a median notch into two fins; nostril 

 just in front of the eyes and opening into a blind 

 sac which does not communicate with the 

 pharynx; eyes well developed in the adult; 

 mouth suctorial, in the middle of a depressed, 

 funnel-shaped oral plate, called the buccal funnel 

 (Fig. 10), which has a fringed margin and is set 

 with sharp, horny teeth or toothlike tubercles; 

 tongue with sharp rasping teeth; bordering the 

 mouth anteriorly and posteriorly, respectively, 

 are the so-called supraoral and infraoral lamince, 

 horny plates each with 2 or more teeth; intes- 

 .1^.^; 1°-.— Buccal funnel ^ine with Spiral valve; 7 pairs of gill-sacs, the 



01 Reighardt7ia untcolor {from '■ ^ / . , 



Jordan's Guide to the Study external Openings forming a row immediately 



of Fishes, after Gage). ^^^^ ^^ ^^^ ^^^^. ^^^^^ ^ . SpCCicS, in frCsh and 



salt water; i family, the PelromyzonidcB, with about 8 species in the 

 United States. 



Adult lampreys, in the case of most of the species, feed by attaching 

 themselves to fishes and sucking their blood and rasping away the flesh, 

 often killing them, and causing large sores and scars on those they do 

 not kill; they are often destructive to fisheries. The marine species 





