Phylum Chordata 581 



is, from 1 to 3 feet in length, but the great manta ray or devilfish, 

 Manta, may be 17 feet long and 20 feet across. The food of these forms 

 is chiefly molluscs and crabs. Some highly modified rays are the saw 

 fish with its peculiar elongate saw snout, the stingrays with their sting 

 at the base of the tail, and the electric rays with their electric organs. 

 The eggs of many sharks and rays are contained in peculiar H- 

 shaped capsules. The prolonged tendrils of these capsules perhaps en- 

 tangle in the sea weeds and thus stay afloat. They are commonly seen 

 on the shores after being washed up. 



The Chiniaeras. — The chimaeras are strange looking fish with 

 protruding eyes and smooth skin. They have a slender tail, large 

 pectoral fins, and a series of very prominent sense organs that form the 

 lateral line system. Unlike the other Chondrichthyes, the upper jaw 

 of the chimaeras is fused immovably to the cranium. These fish are 

 chiefly mollusc eaters. 



Economic Importance.— In many areas, sharks and skates are 

 used as food, but of greater importance is the oil of the shark liver 

 which has a high content of vitamin A. Inasmuch as the liver is very 

 large in most sharks, this is an excellent source of high quality oil. 

 The number of dogfish shark used for laboratory dissections in colleges 

 constitutes an important business for some marine areas. Shark skin 

 has at times been used as an abrasive known as shagreen. 



*■&>' 



THE CLASS OSTEICHTHYES 



The most abundant of the fishlike animals are the members of this 

 class. Nearly all forms are characterized by the presence of a true bony 

 skeleton and in having a body covered with scales. 



The members of this class are found in all types of fresh water, in 

 all parts of the ocean, and a few are even temporary invaders of the land. 

 As would be expected from their general abundance, these fish are a very 

 successful group of animals that show great variation in size, habits, 

 and appearance. 



In size, they vary from a small Philippine fish (Mistichthys) of 

 less than one-half inch in length to forms such as the giant ocean sun- 

 fish (Mola mola) which has been known to attain a weight of more 

 than a ton and a length of at least 11 feet. In form the fish are so 

 varied as to make generalizations impossible. There are those that have 

 the familiar torpedo-shaped body, some are flattened, some are enor- 



