CHAPTER XI 



Squid, 

 Octopus and Cuttlefish 



Class CEPHALOPODA 



Subclass TETRABRANCHIA 



This subclass, which includes the Chambered Nautilus and about 5000 

 species of fossil and extinct Ammonites, is not represented in American 

 waters. The living species of Nautilus from the Indo-Pacific are character- 

 ized by a large, chambered, external shell, by two. pairs of gills, and by their 

 numerous suckerless arms. 



Subclass DIBRANCHIA 



All of the living cephalopods with the exception of Nautilus belong to 

 this subclass which is characterized by animals that have one pair of gills, 8 

 or 10 arms which bear rows of suckers, and whose shell is internal or en- 

 tirely absent. 



Order DECAPODA 

 (Spirula and Squid) 



With 10 arms, 2 of which are the long tentacular arms; body long and 

 cylinder-shaped. An internal shell is present in most cases, and nmv be cal- 

 careous (the cuttlebone) or thin and horny (squid pen). The small suckers 

 on the arms are usually set on small stalks or peduncles and their apertures 

 are armed with horny rings or hooks. 



Fajnily SPIRULIDAE 

 Genus Spirula Lamarck 1799 



Spirula spirula Linne Common Spirula 



Figure 98 



Cape Cod to the West Indies. Worldwide. 



478 



