PHYLUM ARTHROPODA 



217 



parasitized that the whole physiology is 

 seriously affected. 



Many interesting crustaceans belong to 

 the subclass Malacostraca. A few will be 

 described here, beginning with the sow bugs. 

 A terrestrial species Oniscus (Fig. 110), 

 about 16 mm. long, is slate-colored, spotted 

 with white, and is common under stones, 

 bark of logs, etc. It breathes with gills and 

 must therefore live in a moist place. The 

 body is oval and flat, which enables it to 



creep into crevices; and the "legs" are ap- 

 proximately equal in size. 



Beach fleas live on beaches where they 

 bury themselves in the sand. They can leap 

 with agility but do not bite. The common, 

 long-horned, beach flea (Fig. 121), is about 

 one inch long, has a laterally flattened body 

 like that of a flea, and has legs adapted for 

 leaping. It feeds on decaying animal and 

 vegetable matter and is a valuable scaven- 

 ger on many sand beaches. 



Fiddler crab 



Edible or blue crab 



Figure 121. Representative malacostracans in their respective habitats. 



The fresh-water scud, Gammarus (Fig. 

 110), is also an amphipod, but lives in fresh- 

 water ponds and streams and swims instead 

 of leaps. It is whitish and about 15 mm. 

 long. 



Our most important edible crustacean is 

 the American lobster, Homarus, a near rela- 

 tive of the crayfish. The American lobster 

 has probably been more intensively studied 



than any other marine animal with the pos- 

 sible exception of the American oyster 

 (Ostrea). These lobsters live in the sea 

 along the Atlantic Coast. They are not red 

 when alive, but usually dark green with 

 darker spots and yellowish underneath. They 

 may grow to a length of over 2 feet and 

 to a weight of over 30 pounds, but most of 

 those caught in lobster pots are less than 



