THE PHYLUM MOLLUSCA 



265 



form a protective coat, and young squids hatch in two or three weeks. 

 Development in the cephalopods is direct, the yolky eggs producing 

 young that resemble the aduks. 



115. Other Cephalopods 



The nautikises, with tour gills, belong to the order Tetrabranchiata, 

 which is presumed to include most of the fossil cephalopods. All other 

 living cephalopods have two gills, and belong to the order Dibranchiata. 

 In addition to the common squids and octopuses, the group includes the 

 cuttlefish (Fig. 14.2), whose internal shell is used as a source of lime for 

 canaries, and the deep-sea giant squids. The latter are the largest living 

 invertebrates, having bodies at least 20 feet long with tentacles more 

 than 35 feet long. They were first known from the marks of their suckers 

 on the skin of the sperm whale, which were j^often over an inch in 

 diameter, and from their jaws in the whale's stomach. These squids are 

 the major food of the sperm whale, which dives to great depths to hunt 

 them. Rarely a dying giant squid comes to the surface or is washed 

 ashore (Fig. 14.17). 



Octopuses (Fig. 14.18) lack the tentacles present in squids and cut- 

 tlefish. They also differ from the other Dibranchiata in having suckers 

 that lack stalks and teeth, and in having no shell whatsoever. 



Small octopuses survive well in aquariums where observers are dis- 

 covering that they liave a surprisingly high order of intelligence. They 

 are able to make associations among stimuli and in general show an 

 adaptability of behavior that more closely resembles that of the verte- 

 brates than the more stereotyped patterns of other invertebrates. Oc- 



Figure 14.17. A "small" relative of the giant squid, the oceanic squid, Ommastrephes 

 caroli. This remarkably intact specimen was stranded. A meter ruler gives the scale. 

 (Courtesy Douglas P. Wilson.) 



