THE STARFISH AND SOME ALLIES 231 



means that some accident has befallen the irregular speci- 

 mens, and that new arms are being formed to take the place 

 of those that were lost. It has been found that a starfish 

 deprived of all its arms will, under favorable circumstances, 

 reform all five ; but one that has suffered an injury as exten- 

 sive as a cut through the entire disk probably never survives. 

 Serpent Stars and Basket Stars. The serpent stars and 

 brittle stars (Ophioder'ma) have slender arms which are 

 much more sharply marked off from the disk than are those 

 of the common starfish. They are much less abundant 

 than the common starfish, and being nocturnal in habits 

 are rarely about in the daylight. The tube feet play no 

 part in the locomotion of these animals, for the flexible 

 arms move very readily and, clasping around objects, move 

 the entire body much more rapidly than is possible to the 

 common starfish. The food is chiefly small organisms and 

 decaying organic matter. The basket star (Gorgonoceph'alus) 

 lives in the depths of the ocean, where the pressure of the 

 water is very great. The arms are very finely branched. 



The Sea Lily 



At the present day we find here and there in the compara- 

 tively warm, deep waters of the ocean, animals like that 

 shown in Fig. 125 (Pentacri'nus bla'kei). In past geological 

 eras the crinoids to which the sea lily belongs were very 

 widely distributed, and fossil remains are abundant in many 

 localities. Members of the genus Pentacrinus may be ob- 

 tained by dredging in the deep waters about Porto Rico, 

 and in the South Pacific and the Indian oceans. 



The sea lily is a relative of the starfish and the basket 

 star. The central disk and the radial arrangement of the 

 arms make the resemblance striking. The sea lily is differ- 

 ent from the starfish and the basket star in having a long 



