222 



ECTOPROCTA THROUGH ECHIUROIDEA: 



such portions are used for "pearl" buttons. Certain 

 uses are strictly modern. Shells are now a source of 

 lime. An important recreational activity in coastal 

 areas is clam-digging. 



Not all characteristics of pelecypods are beneficial 

 to man. The burrowing of shipworms in wharf pil- 

 ings causes millions of dollars damage annually in 

 the United States alone. At one time these wood 

 borers caused fatalities at sea because their boring 

 caused wooden boats to collapse. All in all, even 

 today, the value of this group to man far exceeds the 

 damage some individuals cause. 



CLASS CEPHALOPODA (Nautili, Squids, and Octopuses) 



Diagnosis: bilaterally symmetrical and unseg- 

 mented; body mostly a well-developed head with 

 eyes; radula present; foot modified into tentacles 

 (arms); siphon present and used for jet-propelled 



locomotion; shell undivided, conspicuous and ex- 

 ternal in nautili, reduced and internal or absent in 

 other species (Figure 13.9). 



The nautili, squids, and octopuses are all marine 

 predators of fish, crustaceans, worms, and other 

 mollusks. Little is known about the habits of the 

 larger squids, but some smaller ones swim in large 

 schools, from which they may pursue their prey and 

 kill it by a bite. Octopuses are active at night or 

 during the early evening hours and tend to live alone. 

 At night they search cracks and crevices for possible 

 food animals. Some of the cephalopod fish predators 

 have an instinctive behavior pattern which causes 

 them to bite fish in a manner to cut the spinal cord. 

 It is not generally known that octopuses secrete a 

 poisonous substance that quickly immobilizes or kills 

 its prey, but these animals cannot seriously be con- 

 sidered dangerous to man. The author and many 

 others have had underwater encounters with large 



Figure 13.9 Class Cephalopoda, cephalopod types: above, Loligo, a squid, marine; right, Ar- 

 gonaufo, a paper nautilus carrying its shell, marine; below. Octopus, octopus or devilfish, ma- 

 rine. 



