468 



ECHINODERMATA ASTEROIDEA 



CHAP. 



immediate contact with the adambulacral, whilst in Luidia it 

 is separated from it by a small intermediate plate. 



Astropecten irregularis is a very common species on the coast 

 of Britain, and a study of its habits when in captivity has 

 thrown a great deal of light on many obscure points in the 

 anatomy of the Paxillosa. Owing to the loss of suckers it is 



Fig. 201. Oral view of Archaster bifrons. x f . (From Wyville Thomson. ) 



unable to climb over rocks and stones like the ordinary species, 

 but it runs over the surface of the hard sand in which it lives 

 by means of its pointed tube-feet. The arms are highly 

 muscular, and the animal when laid on its back rights itself by 

 throwing the arms upwards and gradually overbalancing itself. 

 The loss of suckers has also rendered Astropecten and its 

 allies incapable of feeding in the manner described in the case 

 of Asterias rubens. They are unable forcibly to open the valves 

 of shell-fish, and the only resource left to them is to swallow 

 their prey whole. The mouth is consequently wide, and the 



I 



