PHYLUM ECHINODERMATA 



207 



dance in rocks from very early times, and many limestone strata are 

 filled with such fossils. Among these are spines and plates, sections of 

 the stems of crinoids, and in some cases the crinoid body, very nearly 

 perfect. At the present time echinoderms are widely distributed and 

 abundant in all seas. The phylum is one of the few which has always 

 been exclusively marine. 



Pir>nu/es 



Aboral 

 tetifac/es 



Fig. 115. — A feather star, .4 w^erfon sp. From a preserved specimen. Natural size. The 

 animal is in a breeding condition as shown by the dilatation of the base of the pinnules. 



Of this phylum only starfishes and sea cucumbers are of much eco- 

 nomic importance. As has been previously indicated, the starfishes 

 are enemies of the oyster. Sea cucumbers are used as food among the 

 islands and along the shores of the South Pacific Ocean and in China, 

 the animals being dried and passing as articles of commerce under the 

 names of heche-de-mer and trepang. 



