OYSTERS, CLAMS, MUSSELS 



233 



and wonderfully irridescent. It is much prized for making 

 buttons and for other purposes for which mother-of-pearl 

 is used. Very beautiful and valuable baroque pearls are some- 

 times found in the abalones. The meat is dried or canned 

 and used for stews or chowder. Large quantities of dried or 

 canned abalone meat are shipped each year to China. 



The nudibranchs or sea-slugs are doubtless the most beauti- 

 ful of all the molluscs. They are without a shell, and the 

 gills are usually in the shape of delicate, freely projecting tufts 

 often arranged in rows along the back. The gills, and indeed 

 the whole animal, are often most strikingly and beautifully 

 colored. 



FIG. 108. Three Pacific coast nudibranchs; Doris tuberculata (in 

 lower left-hand corner), Echinodoris sp. (upper one), and Triopha modesta 

 (at right). 



Squids, Cuttlefishes and Octopi. Both in habits and 

 structure the squids, cuttlefishes and octopi, or "devil-fishes," 

 differ greatly from the other members of this branch. Most 

 molluscs move but little or not at all except as larvae, but the 

 Cephalopoda are very active all their life, swimming swiftly 

 through the water. The name Cephalopoda refers to the fact 

 that the foot assumes the appearance of a number of arms or 



