LIFE IN THE OCEAN — CLARK 377 



Besides the very small crustaceans, the chief plant eaters of the 

 open ocean are curious and delicate little mollusks, the " sea butter- 

 flies," or pteropods, and their allies. But while some forms of these 

 eat plants, most of them live upon minute plant-eating animals, 

 mostly small crustaceans and other mollusks. There are, as com- 

 pared with the crustaceans, relatively few kinds; but some of them 

 occur in incredible numbers, and in the seas about Greenland and in 

 other places they form an important part of the food of the whale- 

 bone whales. So abundant are some of the shell-bearing species that 

 in various parts of the Gulf of Mexico, the Mediterranean, the Bay 

 of Biscay, and elsewhere the sea bottom is more or less exclusively 

 composed of their dead remains, just as in other places it is almost 

 entirely composed of the shells of the foraminifera or the frustules 

 of diatoms. 



The third method of devouring the minute oceanic plants is by 

 filtering them from the water and thus concentrating them. The 

 only oceanic animals that have recourse to this process are the salps 

 and the appendicularians, queer creatures allied to the sea squirts, 

 and certain of the smaller fishes, like the menhaden. Their strain- 

 ing apparatus is most wonderfully efficient, and it is surprising to 

 learn, from looking at the contents of their stomachs through a mi- 

 croscope, how small is the size of some of the organisms they capture. 



THE ANIMAL LIFE OF THE OPEN SEA 



In the bodies of the small crustaceans, the pteropods and allied 

 mollusks, the salps and their relatives, the foraminifera, and a few 

 other types, the nutritive matter represented by the microscopic 

 plants is reassembled into units of appreciable size. Upon these 

 units, for the most part upon the crustaceans which represent the 

 most abundant and most generally distributed of these units, feed 

 all the other creatures of the open ocean, directly or indirectly. 



Consuming these directly are larger crustaceans and mollusks, 

 numerous fishes, the herring and herringlike fishes, flying fishes, the 

 young of all, or nearly all, other marine fishes, etc., the larger salps, 

 the jointed or annelidan worms, the nemerteans, the arrow worms or 

 chsetognaths, the whalebone whales, the smaller jellyfishes, the cteno- 

 phores, and the very few pelagic echinoderms. 



Upon these larger animals, but especially upon the fishes, live 

 very large and formidable jellyfishes, many kinds of fishes ranging 

 in size up to the basking-, whale-, and other giant sharks, reaching a 

 length of from 40 to 70 feet, the smaller members of the whale tribe, 

 the porpoises, dolphins, etc., and the squids and cuttlefish, some of 

 which are very large, one reaching a length of 55 feet. The squids 

 and cuttles form almost the entire food of the great sperm whale, 

 the bottlenose, and the other toothed whales. 



