70 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 cling to rocks. In the 
gobies the united ventrals have some adhesive power. The 
blind goby (Typhlogobius californiensis) 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 (Liparidide) and lumpfishes 
(Cyclopteride) the united ventral fins are modified into an 
Fig. 52.—Clingfish, Caularchus meandricus (Girard). Monterey, California. 
elaborate circular sucking-disk. In the clingfishes (Gobiesocide) 
the sucking-disk lies between the ventral fins and is made in 
part of modified folds of the naked skin. Some fishes creep 
over the bottom, exploring it with their sensitive barbels, as 
the gurnard, surmullet, and goatfish. The suckers (Catostomus) 
test the bottom with their thick, sensitive lips, either puckered 
or papillose, feeding by suction. 
Lampreys and Hagfishes.—The lampreys sek the blood of 
other fishes to which they fasten themselves by their disk-like 
mouth armed with rasping teeth. 
The hagfishes (Myxine, Eptatretus) alone among fishes are 
truly parasitic. These fishes, worm-like in form, have round 
mouths, armed with strong hooked teeth. They fasten them- 
selves 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 
