CLASS CYCLOSTOMATA 



415 



1. The Lamprey — Petromyzon 



Petromyzon marinus, the sea lamprey (Fig. 352, C), 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 cur- 

 rent, progresses by darting suddenly forward and attaching itself 

 to a rock by means of its suctorial 

 mouth. In the spring the lamprey 

 ascends the rivers to spawn. 



External Features. — The lamprey 

 reaches a length of about three feet. 

 Its body is nearly cylindrical, except 

 at the posterior end, where it is 

 laterally compressed. There is no 

 exoskeleton. The skin is soft and is 

 made slimy by secretions from epi- 

 dermal glands. It is mottled greenish 

 brown in color. A row of segmental 

 sense pits, the lateral line, lies on each 

 side of the body and on the head. 

 The mouth (Fig. 353, mth) lies at the 

 bottom of a suctorial disc, the buccal 

 funnel {buc.f), and is held open by a 

 ring of cartilage (Fig. 354, 2). Around 

 the mouth are a number of papilla Parker.) 

 (Fig. 353, p) and horny teeth (t x -t 3 ). 



Just beneath the mouth is a piston-like tongue which also bears 

 teeth (P). On each side of the head is an eye, and, posterior 

 to the eye, seven gill-slits (Fig. 352, C). Between the eyes 

 on the dorsal surface is a single opening, the nasal aperture 

 (Fig. 355, na"). The anus opens on the ventral surface near 

 the posterior end; just behind it is the urinogenital aperture in 

 the end of a small papilla. There are two dorsal fins and one 

 caudal fin (Fig. 352, C), 



Fig. 353. — Ventral view 

 of the head of Petromyzon ma- 

 rinus. buc.f, buccal funnel; 

 mth, mouth ; p, papillae ; 

 /', P, I s , teeth of buccal funnel; 

 / 4 , teeth of tongue. (From 



