242 THE BIOLOGY OF MARINE ANIMALS 



sharks sight their prey and some have peculiar feeding habits, such as the 

 thresher shark (Alopias) which herds shoals of small fishes into compact 

 masses by threshing the water with its tail, before rushing in to devour them. 

 The rough dogfish Scyliorhinus hunts chiefly by scent, mostly but not 

 exclusively near the bottom, and feeds on anything which comes its way 

 (50,93). " 



Fishes from deeper pelagic waters are frequently much modified in 

 connexion with feeding, but naturally the habits of these animals are 

 subject to inference. Teeth are often long and fang-like and the jaws 

 flexible and distensible, so that very large prey can be captured (Chauliodus, 

 Chfasmodon, etc., Fig. 5.28). The mechanics of these distensible jaws are 

 described in some detail by Tchernavin (99). Conditions of feeding are 

 certainly peculiar in the dark, sparsely populated waters of the deep sea: 

 Anglers (ceratioids), which have a luminous fishing lure, are believed to 

 attract their prey within reach by this device (Fig. 13.8, p. 547). Long barbels, 

 occurring for example in Eustomias, may provide tactile appreciation of 

 prey (Fig. 13.18, p. 556). Very large gape and distensible stomach are 

 significant adaptations to few and infrequent meals. 



Carnivorous fishes living on or near the sea bottom may be classed as 

 active foragers, stalkers and purely sedentary forms which sit and wait for 

 prey to come near. Active foragers which depend on sight hunt only by 

 day, at least in shallow waters. The cod, for example, is a roving fish which 

 snaps at anything within its reach on or near the bottom. Foraging is 

 largely visual but is aided by a barbel which is employed as a tactile or 

 gustatory organ. A strictly bottom dweller is the dragonet Callionymus. 

 This fish swims along near the bottom and comes to rest at intervals with 

 the body poised on the large pectoral fins. In this manner it explores a 

 wide area of the sea floor and captures such slow-moving bottom forms as 

 Crustacea, echinoids and worms. The lemon dab Microstomas kitt hunts 

 mainly tubicolous polychaetes. Coming to rest at intervals with head raised, 

 it scans its neighbourhood with movable eyes and, sighting a worm, 

 suddenly pounces upon it. 



Certain other bottom fish depend largely on tactile sense when foraging. 

 The sole Solea solea, for example, has a dense mass of tactile villi on the 

 lower cheek. When feeding it creeps slowly over the bottom, exploring 

 with its snout and feeling objects in its path with the sensitive cheek villi. 

 Its food consists of errant polychaetes, small crustaceans, molluscs and 

 ophiurans. The gurnard Trig/a lineata is another form which crawls over 

 the bottom by means of long pectoral filaments (Fig. 5.29). As the fish 

 creeps along, the filaments are kept in constant movement, exploring the 

 bottom: whenever anything promising is encountered, the fish suddenly 

 whirls along and swallows it or subjects it to further examination. The 

 filaments are richly provided with sensory cells acting as taste receptors. 

 Rays are thought to feed largely by scent. On encountering small fish and 

 Crustacea they dart over it, cover it with body and pectoral fins, and devour 

 it at leisure (42, 82, 89, 93, 94). 



