precious tusk shell of the North Pacific is D. pre- 

 tiosiim. In New Guinea, heavy tusk shells as much 

 as 5 inches long are used by native people as decora- 

 tions thrust through holes in the septum of the nose, 

 in the lower lip, or in the ear lobes. 



The Octopus and Its Kin 



( Class Cephalopoda ) 



For almost everyone, the octopus holds a fearful 

 fascination. This had led man to call it the "devil- 

 fish." Actually, octopuses are extremely shy, retiring 

 creatures, eager to slither out of man's way. The big- 

 gest of them has an arm spread of about 12 feet, but 

 the average octopus can barely stretch across a circle 

 1 foot in diameter. All of these animals seem com- 

 pletely unwilling to bite, even if provoked. 



The same denial cannot include the octopus' kin, 

 for some squids bite viciously if handled. Yet no 

 member of the class Cephalopoda has been reliably 

 recorded to have attacked a person without provoca- 

 tion. Admittedly, all of them possess a pair of ar- 

 mored jaws suggesting those of a parrot, except that 

 the lower half of the beak closes outside the upper 

 half. These jaws supplement a typical molluscan 

 radula and aid the animals in tearing apart the crabs 

 and other foods in their strictly carnivorous diet. 



The distinctive feature of the octopus and its kin is 

 the eight or more arms that extend from the head and 

 are used in capturing food. They make the animal 

 "head-footed" and give class Cephalopoda its name. 

 Most cephalopods have also a pair of large eyes re- 

 sembling those of man and other vertebrate animals 

 to a degree that is uncanny, for the organs arise en- 

 tirely difi'erently in the embryo. 



Millions of years ago, all cephalopods supposedly 

 used the mantle to secrete an external shell, and 

 were able to take shelter inside the secretion. Today 

 this habit is continued only by two different "living 

 fossils," the several species of Nautilus in the south- 

 west Pacific and the strange little Spinila at the upper 

 edges of the abysses in the Atlantic and Indian 

 Oceans. 



The common cuttlefish Sepia officinalis of the 

 Mediterranean and eastern Atlantic (Plate 75) pro- 

 duces an internal limy shell of degenerate form — the 

 "cuttlebone" sold to hang in cages with canaries and 

 other pet birds. Squids, such as Loligo, gain some 

 support from a concealed relic of the shell, the chi- 

 tinous "pen," which may be shaped somewhat like 

 the feather of a quill pen, or narrow and slightly 

 curved like a sword blade. The octopus lacks all 

 traces of a hard shell. Yet all cephalopods retain the 

 U-shaped digestive tract which is helpful to an ani- 

 mal whose body is covered by a conical external 

 skeleton. 



X-rays disclose a dense population of sliipworms, 

 both the larger Teredo and the smaller Bankia, as 

 they sabotage a timber exposed to the sea. These 

 degenerate mollusks use their small shell valves as 

 boring tools in making chambers for their bodies. 

 Apparently they use the wood only as a home, but 

 the damage done is comparable to that of wood-eating 

 termites on land. (Florida. Charles E. Lane) 



194' 



