THE LOWER FISHES 133 



methods but are not so host-dependent as to have become nearly as anatomically 

 altered as the tapeworm. Some biologists prefer that they be called "specialized 

 carnivores," but since they feed on living prey, the term "parasite" is better. 

 As is so often the case with parasites, the body form has tended to become 

 simple and degenerate, in this case elongate and with a poorly developed 

 skeleton of cartilage. The hagfishes tend to be scavengers, too, since they feed 

 on dead or dying prey. 



The Agnatha are distinct from all succeeding vertebrates because of their lack 

 of paired fins and jaws. In the modern forms the mouth is merely a round 

 disc with a hole in the middle containing a rasping tongue. This mouth acts 

 as a powerful sucking mechanism. Hence, these forms are sometimes called 

 the "Cyclostomata" ("round mouth"). With this mouth they are able to do 

 such things as grasp and bore into their fish prey, build a nest of stones, anchor 

 themselves to rocks, pilings, or even boats, and grasp their mates while breeding. 



Because of the lack of paired fins, they are not very good swimmers. Though 

 they can dash for prey at considerable speed, their steering is not as good as 

 that of fish with more fins and shorter bodies. One does not see them swimming 

 about nearly as much as one sees them attached to some item of substrate 

 waiting to strike, almost snakelike, at some unlucky fish that happens to pass 

 their way. 



The two groups of agnathans are distinct, and each attacks its prey in a quite 

 different way. 



LAMPREYS: Family Petromyzontidae 



There are usually seven gill openings on each side, and there are no barbels 

 on the snout. The eves are large, and the dorsal fin is discontinuous. Lampreys 

 swim vigorously but not too efficiently, and are active, voracious animals. They 

 attach themselves to fishes, preferably at the softer throat, side, and belly 

 regions, and scrape away the skin with the rasping tongue in order to suck 

 the blood and eat some of the flesh. Their saliva is an anticoagulant. Very often 

 this either kills the prey outright or so weakens it as to cause delayed death. 

 Larger fishes do recover. They prefer the soft-scaled fishes. Hard scales seem 

 to be protection against attack. 



Not much is known of lampreys in the sea, though they spend most of their 

 lives there. They are most commonly observed in streams in the spring, where 

 they go to breed after a certain unknown number of maturing years in the sea. 

 In this respect, they are like salmon and are said to be anadromous. During their 

 journeys up rivers, they perform remarkable acrobatics in climbing rapids and 

 low falls with the aid of their sucking mouths. In the riffles, a nest is scooped 

 out of gravel and large numbers of small eggs are laid. These hatch into 

 Ammocoetes larvae which are nonparasitic but look much like the adults. After 

 spending three to five years in fresh water, having attained a 6-inch length, 

 the Ammocoetes go to the sea to mature, and the breeding cycle begins again. 



Lampreys may become landlocked as they have in the Great Lakes, where 

 they have all but destroyed the lake trout and whitefish industries. In spite of a 

 repulsive appearance, they are edible and quite tasty. Formerly they were a 

 popular food in New England and in Europe. 



Lampreys are found in all temperate seas. 



