THE INVERTEBRATE LEGIONS 125 



Squids and Octopuses: Class Cephalopoda {"head foot") — Figure 41 



In this group, there is a definite tendency to lose the shell and to become 

 active and predatory. Some cuttle fishes, Sefia, still have a shell known as 

 "cuttlebone," but it is entirely internal. The common squids, Loligo, have a 

 fragile pen-shaped shell buried in their flesh and the octopuses are without 

 shells. In all cephalopods the foot is developed into a circlet of tentacles around 

 the mouth. The mouth has a parrotlike beak, and the bites of cephalopods 

 are poisonous, sometimes dangerously so. Although these animals are not often 

 inclined to bite, their means of defense centered elsewhere, they should be 

 handled only with care. While the tentacles are not dangerous, the bites from 

 octopuses have been known to result in death. 



Defense consists of protective coloration coupled, in the case of octopuses, 

 with secretive habits or, in the case of squids, with speed of swimming. When 

 molested, all cephalopods have the habit of emitting a smoke screen of dark 

 inky fluid and then making a hastv retreat. In some deep sea squids, the ink 

 is luminescent. 



Cephalopods are the largest, speediest, and most active of invertebrates. The 

 giant squid, Architeuthis, is a favorite food of the sperm whale, lives in the deep 

 sea, and reaches a length of about 50 feet including the long tentacles. Some 

 octopuses have an armspread of over 12 feet. Octopuses are shy animals, but 

 large ones are less shy than small ones. 



The nervous system of cephalopods is extremely well developed. Their giant 

 nerve fibers conduct nervous impulses at a very rapid rate. Their eyes are very 

 much like mammalian eyes, and these animals see very well. These features 

 provide cephalopods with the extremely fast reflexes necessary for active 

 predatory animals, but they do not necessarily imply intelligence, for which 

 integration of senses and actions is needed (Chapter 2). In fact, the intelligence 

 of these animals, like their ferocity, is often overestimated. 



Cephalopods are the original inventors of jet propulsion. They draw water 

 into the mantle cavity and forcibly eject it from a siphon. They can change 

 direction by moving the siphon, but they usually swim backwards. 



The color changes of cephalopods are the most rapid and striking to be seen 

 in the entire animal kingdom. By means of rapidly redistributing pigments in 

 their pigment-bearing cells or chromatophores, they can cause complete change 

 of color or even waves of color to pass over their bodies in a matter of seconds. 

 Most cephalopods match background by means of color change. They also 

 change colors when feeding or in response to stimuli leading to fear. 



The tentacles of cephalopods are organs used for food-catching, movement 

 (octopuses crawl), and reproduction. These tentacles bear suckers, the power 

 of which is remarkable. Even a small octopus of only a few feet in tentacle 

 spread can hold onto a rock so as to be almost immovable. Care should be taken 

 by the diver not to let an octopus grasp him and a rock at the same time. This 

 the octopus will not do as an aggressive action, but only if it is first molested. 



During copulation, sperm is transferred to female cephalopods with one 

 specialized tentacle which usually has the suckers reduced in number and size. 

 In some octopuses, namely the paper argonaut, Argonauta, and Philonexis, the 



