Phylum MoUusca and Minor Eucoelomate Phyla 481 



usually on rocks, and the female remains with them during the develop- 

 mental period. She carefully aerates and cleans them during the in- 

 cubation period. Thus their survival is well assured. She does not 

 take any food during this time which may last as long as six weeks. 



Fig. 158. — Some members of the class Cephalopoda, a, Argonauta, the cham- 

 bered nautilus; b, Loligo, the squid; c, Octopus, the octopus; d, Sepia, the cuttlefish; 

 e, male argonaut; /, Architeuthis, the giant squid; g, Nautilus, the pearly nautilus. 



The argonaut is a peculiar member of the octopus group. The 

 female has a shell composed of a spiral structure and secreted by a 

 pair of the arms rather than by the mantle. The chief function of the 

 shell is to carry the eggs. The male has no shell, and during mating a 

 portion of one arm with the attached spermatophore is actually detached 

 and left in the mantle cavity of the female. 



The churnhered nautilus is the only one of this group to have a 

 true shell into which the body can be withdrawn. The shell is divided 

 into chambers by septa, and the animal occupies only the outermost 

 one. This animal dwells along tropical coasts in moderate depths of 

 water. The nautilus is the sole survivor of a once abundant group of 



