Chap. 29 



ARTHROPODS CRUSTACEANS 



573 



Fig. 29.2. A crayfish (upper) and a mayfly (lower) display the leading char- 

 acteristic of all arthropods, segmented bodies combined with segmented append- 

 ages. The crayfish is an example of this plan in an arthropod that lives in the 

 water, and the adult mayfly of an arthropod adjusted to the land. Arthropods have 

 carried the basic plan into almost every corner of the earth. 



small crustaceans are the main food of the great blue whale; the larger ones 

 are human food throughout the world. 



A Connecting Link. Peripatus is the only living animal that comes near 

 being a common relative to annelid worms and to arthropods (Fig. 29.3). It 

 is a couple of inches long, has a velvety skin and resembles a caterpillar. It 

 belongs to a small group, the Onychophora ("claw bearing"), considered a 

 phylum by some and a class by others. It lives in tropical forests in such 

 separated regions as Australia and South and Central America, suggesting 

 that it once may have been widely distributed and is now disappearing. It dif- 



