HIGHER CHORDATES 



271 



ACENTROPHORUS 



PARASEMIONOTUS 



Figure 16.6 Restoration of some fossil Actinopterygii; Acenfrophorus, Superorder Chondrostei; 

 Parosemionofus, Superorder Holostei. (From Malcolm Jollie, Chordate Morphology, Reinhold 

 Publishing Corp., New York, 1962.) 



predators or scavengers on dead fish. Lampreys are 

 found in both salt and fresh water, but hagfishes are 

 strictly marine. Many species throughout the entire 

 class have both a well-developed, rasp-like tongue, 

 which is used to burrow into the true fishes they 

 attack, and a sucker-like mouth, which is used to at- 

 tach to fishes and other objects. These two structures 

 are best developed in two of the feeding typies — the 

 parasitic forms that use mouth and tongue to gain 

 nutrients from the body fluids of their hosts, and the 

 predaceous species that literally rasp and eat their 

 way through their prey. 



Reproduction is interesting in both orders. The 

 hagfishes lay large (to slightly over an inch in diam- 



HOLOPTYCHIUS 



eter) shell-covered eggs on objects in the sea and 

 miniature adults hatch from the eggs. The young 

 hagfishes first develop into males and later the males 

 transform into females. On the other hand, both 

 marine and fresh-water lampreys lay their eggs in 

 fresh water, all lampreys migrating to their breeding 

 grounds. To reach the clear-water breeding grounds, 

 lampreys may attach to a fish or boat going in the 

 right direction. Upon reaching the breeding site, they 

 construct a small hollow to receive the large number 

 of eggs — some lamprey females layabout a quarter of 

 a million eggs. Perhaps this great expenditure of en- 

 ergy is the reason why all adults die after spawning. 

 After the eggs develop awhile, they hatch into lancet- 



EUSTHENOPTERON 



DIPTERUS 



OSTEOLEPIS 



Figure 1 6.7 Restoration of some fossil Choanichthyes; Holoptych'ius, Eusthenopferon, and 

 Osfeolepis, order Crossopterygii; D'lpterus, Order Dipnof. {From Malcolm Jollie, Chordate 

 Morphology, Reinhold Publishing Corp., New York, 1962.) 



