ASTERIAS, OPHIURA 219 



OPHIUROIDEA 



OPHIURA (Serpent-star) 



These animals live more or less concealed in crevices, 

 shells, eel grass, etc., and may be obtained either by dredging 

 or by pulling a dip net through eel grass. They are not con- 

 spicuous objects along the shore, as are starfish, and they 

 differ essentially from starfish in their method of locomotion 

 and their method of feeding. 



Examine a specimen and notice: 



1. The appearance of the disk and arms. Are the spines 

 similar to those of Asterias? The arms are more flexible. In 

 what direction do they bend easiest? 



2. The five buccal plates, one of which bears a madreporic 

 opening that is not easily seen. 



3. The size and shape of the mouth. 



4. The ambulacral grooves. Are they distinct? 



5. The ambulacral feet. Do they have suckers? How 

 are they arranged? 



6. The openings to the bursae, near the bases of the arms. 

 Most ophiurans have five pairs of these openings, one for 

 each bursa, but Ophiura has ten pairs, two for each bursa. 



Draw an oral view of a specimen. 



Place a living specimen in a dish of sea water and watch 

 its movements. 



1. Compare the rate and method of movement with As- 

 terias. 



2. Are all of the arms used in progressing in the same 



way? 



3. See if the arms can be used interchangeably or if a 

 certain one is always directed forward. 



4. Are the ambulacral feet of any service? Do they ad- 

 here? The internal structure shows that the stomach is not 

 eversible and that the hepatic caeca do not extend into the 

 arms. Is there any correlation between these two facts? 



The nervous and water- vascular systems are very similar 

 to those of Asterias, but here the former lies within instead of 



