198 



Adaptations of Fishes 



fishes attach themselves by a large sucking-disk on the top of 

 the head, which is a modified spinous dorsal fin. They do not 

 harm the shark, except possibly to retard its motion. If the 

 shark is caught and drawn out of the water, these fishes often 

 instantly let go and plunge into the sea, swimming away with 

 great celerity. 



Sucking-disks of Clingfishes. — Other fishes have sucking- 

 disks differently made, by which they chng to rocks. In the 

 gobies the united ventrals have some adhesive power. The 

 blind goby {Typhlogobiits califoriiiensis) is said to adhere to rocks 

 in dark holes by the ventral fins. In most gobies the adhesive 

 power is slight. In the sea-snails {Li parididcc) and lumpfishes 

 (Cvclopteridcc) the united ventral fins are modified into an 



Fig. 1.50. — Cliugfish, Cuiihirchus mirandricus (GirarJ). Monterey, California. 



elaborate circular sucking-disk. In the clingfishes (GobiesocidcF) 

 the sucking-disk lies between the ventral fins and is made in 

 part of modified folds of the naked skin. Some fishes creep 

 OA'er the bottom, exploring it with their sensitive barbels, as 

 the gurnard, surmullet, and goatfish. The suckers (Catostomits) 

 test the bottom with their thick, sensitive lips, either puckered 

 or papillose, feeding by suction. 



Lampreys and Hagfishes. — The lampreys suck the blood of 

 other fishes to which they fasten themselves b}' their disk-like 

 mouth armed with rasping teeth. 



The hagfishes {Myxiiic, Epiatiriiis) alone among fishes are 

 truly parasitic. These fishes, worm-like in form, have round 

 mouths, armed wdth strong hooked teeth. They fasten them- 

 seh-es at the throats of large fishes, work their way into the 

 muscle without tearing the skin, and finally once inside devour 

 all the muscles of the fish, leaving the skin unbroken and the 

 viscera undisturbed. These fishes become living hulks before 



