CHAPTER VII 

 TEETH AND FOOD 



Teeth of Cyclostomes and Selachians. Succession of teeth in Sharks and 

 Rays. Different kinds of Shark dentition. Man-eating Sharks. 

 Thresher Shark. Nurse Sharks and Bull-headed Sharks. Teeth of 

 Rays. Dentition of Chimaeras. Teeth of Bony Fishes. Pharyngeal 

 teeth. Depressible teeth. Feeding habits of Pike, Caribe or Piraya, 

 Blue-fish, Lancet-fish, Barracuda. Canine teeth: Chauliodus, Cynodon. 

 Dentition in fishes with mixed diet. Archer-fish. Plankton feeders. 

 Wrasses. Parrot-fishes and Plectognaths. Cyprinids. Stromateoids. 

 Unusual meals. A remarkable " Shark story." 



The mouths of Cyclostomes are armed with horny, tooth-Hke 

 structures, but are devoid of true teeth. The inner surface of 

 the funnel-shaped mouth of the Lamprey {Petromyzon) is 

 studded with conical yellow " teeth," and at its centre, placed 

 above and below, are two horny plates with jagged edges, 

 formed by the enlargement and fusion of several smaller teeth 

 (Fig. 45A) . Similar plates are found on the muscular protrusible 

 tongue, which works like a piston and rasps off the flesh of the 

 fishes on which the Lamprey preys. In the Hag-fishes {Myxi- 

 nidae) the tongue is very powerful, and, apart from a single 

 tooth on the roof of the mouth, the comb-like lingual plates 

 represent the only dental armature. When worn out, the teeth 

 of the Cyclostomes are replaced by new ones developing 

 beneath those actually in use. 



Certain problematical fossils known as Conodonts from the 

 Cambrian, Silurian, and Devonian rocks have been regarded 

 by some authorities as the lingual teeth of extinct Lampreys, 

 but they are of a very different structure, and may not belong 

 to vertebrate animals at all. 



It has been remarked {cf. p. 86) that the teeth of Selachian 

 fishes are essentially similar, both in structure and mode of 

 development, to the dermal denticles covering the body, and 

 a study of an unhatched embryo of a Dog-fish provides un- 

 deniable evidence in support of this statement. The outer 

 skin is continued over the edges into the cavity of the mouth 

 itself, and the close-set, spiny denticles form a continuous 

 undifferentiated series (Fig. 50A). It is only as growth proceeds 



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