ECHINODERMATA 



93 



able degree, and when seized by one arm often separate it from 

 the rest of the body close to the central disc, and thus escape 

 (Fig. 84). 



Fig. 82. Pentaceros reticularis, oral aspect; common in Florida; the largest starfish on 

 the eastern shore of the United States; attains a diameter of thirty or more centimeters. 

 (Photographed from a dried specimen by the author.) 



CLASS III. OPHIUROIDEA 



The Ophiuroidea (Gr. oc/h?, serpent, and eZSo?, form) are the 

 serpent or brittle stars and the basket fishes. The serpent stars 

 resemble the common starfishes in their general shape, but the 

 arms are much more slender, and 

 of very nearly the same diameter 

 throughout their length (Fig. 85), 

 so that the interradial spaces are 

 much broader. The skeletal plates 

 are often regularly arranged on the 

 aboral surface of the central disc, 

 but the madreporic plate lies in 

 an interradius on the oral surface. 

 Here, too, we find in each inter- 



„_j« • r ivri • Fk;. 83. Culcita pentagularis, aboral 



radius a pair of shthke openings, surfac / ; ie(hu . rcL ( * rom Ludwig . 



ten in all, which lead into pockets Leunis Synopsis der Thierkunde.) 



