stalked barnacles that grow on ships' hulls or floating timbers. But 

 the most familiar and most numerous are the smaller acorn barnacles 

 (stalkless barnacles), small conical turrets of limy plates that in their 

 millions coat the rocks between tide marks. 



The fifth, which includes crabs, lobsters, prawns, and shrimps, 

 is even more familiar. The animals making up this group are called 

 loosely the decapod or ten-legged crustaceans because of their five 

 pairs of legs, one pair or more of which serve also as claws. But 

 there are also a variable number of swimming legs tucked under 

 the abdomen, which in shrimps, lobsters, and prawns is commonly 

 called the "tail." These decapod crustaceans range from tiny 

 shrimps swimming freely in the plankton, or burrowing in the 

 sand, to the many kinds of lobsters and crabs of great and small 

 size. The giant crab of Japan has a body one foot across, its legs 

 spanning six feet. Many shrimps and prawns are luminous, parti- 

 cularly those living in the depth of the oceans. And it is here, too, 

 that the legs of the decapod crustaceans are long in proportion to 

 their body. Their legs serve as stilts that keep the animal's body 

 from settling into the soft ooze coating the bottom. 



The rest of the sea's visible animal inhabitants, apart from some 

 rather puzzling animals known as prochordates, are vertebrates: 

 fishes, a few reptiles (notably turtles and sea snakes), sea birds, 

 whales, seals, and sea cows. This completes the catalogue of marine 

 animals, except for the Protozoa, the single-celled animals of micro- 

 scopic size. But to discuss them here would destroy the sequence of 

 our story. Our understanding of microscopic creatures of the sea 

 has come late in the history of marine biology. The animals we have 

 dealt with so far are all readily visible to the naked eye and have 

 been known by man for centuries. Before biologists could explore 

 the microscopic marine world, certain technological breakthroughs 

 had to be made. 



Among the larger of the decapod crustaceans 

 is the lobster, which has been a favorite 

 food for many centuries. As this 

 drawing made in 1495 by Albrecht Durer 

 shows, the lobster has a segmented body and 

 segmented legs, as do all crustaceans. 



89 



