540 Animal Biology 



at least, are very resistant to freezing temperatures and dryness, thus 

 initiating new food supplies for higher animals after such climatic condi- 

 tions have passed. 



PHYLUM 8— ECHINODERMATA (STARFISH, SEA URCHIN, 

 SAND DOLLAR, ETC.) 



The spines of echinoderms in general are a menace to those who fre- 

 quent the seashores for bathing. The spines of sea urchins are used as 

 slate pencils in certain regions of the world (Fig. 108) . 



Starfishes and other echinoderms are frequently used in experiments in 

 artificial parthenogenesis, autotomy, embryology, and regeneration (Figs. 

 28 and 104 to 107). Starfishes forcibly open great numbers of oysters 

 and clams and use them for food (Fig. 328). The remains of starfishes 

 are frequently used as fertilizer. The eggs of starfishes and sea urchins 

 are used for food. Dried sea cucumbers (class Holothurioidea) , known 

 as "trepang" or "beche-de-mer," are used for food in southern China, 

 Queensland, and the South Pacific islands. 



Geologically, the echinoderms are present from the Pennsylvanian epoch 

 (255 million years ago) of the Paleozoic era down to the present (Figs. 

 320 to 322). Huge masses of limestone are frequently found to be com- 

 posed of the remains of fossilized feather stars (Fig. 112) . 



PHYLUM 9— ANNELIDA (SEGMENTED WORMS) 



Earthworms serve as food for higher animals, and probably even for 

 certain tribes of savages (Figs. 185 to 190). By burrowing through the 

 soil, they permit air and moisture to penetrate to the roots of plants. 

 They rarely attack living plants. The "castings" of earthworms bring 

 the more fertile portions of the soil in contact with the less fertile, thus 

 resulting in a general mixing of it. Charles Darwin estimated that more 

 than eighteen tons of earthy castings may be carried to the surface in a 

 year on one acre of ground by 50,000 earthworms. Earthworms also 

 help to destroy dead plant materials and change them into available 

 and usable types for future living plants. Earthworms have been used 

 experimentally in studies of regeneration and grafting. They may acci- 

 dentally act as intermediate hosts in the transmission of the roundworm 

 or gapeworm (Syngamus trachea). This parasite need not pass through 

 the earthworm as a host in all cases. 



Certain marine, fresh-water, or terrestrial forms possessing setae (class 

 Chaetopoda) have been found as fossils from the Cambrian period (550 



