PHYLUM MOLLUSCA 



293 



• Busycon 

 (Whelk) 



Sea water 



Eubranchus-. 

 (Nudibranch) ' 



Empty shell of' ' ' . .' 

 Urosalpinx '" ' ■:.■ 

 ' • (Oyster drill) .•■.•..•.. •.;.•■::•.':;:'. V} 



Aplysia 

 (Sea slug, sea hare) 



•" • ■ •".'• Strombus- 

 (Giant conch) 



Oui 



Figure 182. Representative gastropods. 



from that of the limpet, and what is left is 

 a rather high-arched disk. Limpets chng 

 tenaciously to rocks. The sea butterflies or 

 wing-footed mollusks (pteropods) spend 

 their lives near the surface of the open sea. 

 They live in vast schools, sometimes cover- 

 ing the sea for many miles. Whales feed 

 on them to such an extent that they are 

 known as "whale food." 



Squids, octopuses, and 

 other cephaiopods 



The cephaiopods are the most highly de- 

 veloped class of mollusks. 



A common squid along the eastern coast 

 of North America from Maine to South 

 Carolina is known as Loligo pealii (Fig. 

 183). The foot of this species consists of 



10 arms bearing suckers, and a funnel 

 (siphon). The arms are used for capturing 

 prey. The funnel is the principal steering and 

 locomotor organ; if it is directed forward, 

 the jets of water forced through it propel 

 the animal backward; if directed backward, 

 the animal is propelled forward. Thus the 

 jet propulsion principle was old in nature 

 before it was applied to the powering of 

 airplanes. The mantle in the posterior re- 

 gion is extended into triangular fins which 

 may propel the squid slowly fonvard or back- 

 ward by undulator}^ movements. 



The pen ( shell ) of this squid is a feather- 

 shaped plate concealed beneath the skin of 

 the back (anterior surface). The true head 

 is the short region between the arms and 

 the mantle collar; it contains two large eyes. 

 The digestive system includes a muscular 



