CHAPTER XXVIII 

 THE LAMPREY EELS AND OTHER CYCLOSTOMES 



The phylum Pisces which contains the fishes may be divided 

 into four subclasses as follows : — 



Subclass i. Cyclostomata. — Lamprey Eels and Hagfishes. 



Subclass 2. Elasmobranchii. — Sharks and Rays. 



Subclass 3. Teleostomi. — True Fishes. 



Subclass 4. Dipnoi — Lungfishes. 



The simplest group of fishlike animals are the lamprey eels 

 and hagfishes. These animals are very seldom seen, since they 

 are aquatic and most of them live in the sea. The species most 

 easily obtained for study in the laboratory is the sea lamprey 

 (Fig. 138, A). This fishlike creature inhabits the waters along 

 the Atlantic coast of North America, the coasts of Europe, and 

 the west coast of Africa. It swims about near the bottom by 

 undulations of its body, or when in a strong current, progesses 

 by darting, suddenly forward and attaching itself to a rock by 

 means of its suctorial mouth. In the spring it ascends the rivers 

 to spawn. 



Form of Body. — The body of the lamprey reaches a length of 

 three feet. The skin is not protected by an exoskeleton such as 

 the scales of the true fishes, but is covered with slimy secretions 

 from the numerous glands embedded in it. As an aid in swim- 

 ming the posterior part of the body is provided with a tail fin 

 and two dorsal fins. 



Mouth and Food. — One of the most striking features of the 

 lamprey is its circular, suckerlike mouth, devoid of jaws (Fig. 

 154). At the bottom of this sucker is a pistonlike tongue which 

 when drawn in creates a partial vacuum, enabling the animal to 



268 



