HOW DO STARFISHES OPEN OYSTERS? 



267 



conical shaped arms, increasing in width from the apex to the base, the 

 united bases forming a more or less marked central body {m, Pig, la). 

 Astropecten auirmtiacus, which is common at Naples, may be taken as 

 the representative of this group.* It lives in places where there is more 

 or less deep sand, half buried in which it pursues its prey. The latter 

 consists, for the most part, of bivalves and gasteropods which also bury 

 in the sand, and the starfish forces them, by means of its flexible tube- 

 feet, into its mouth, which is capable of a very remarkable degree of 

 extension. The number and size of these molluscs which an Astropecten 



Fig. la. 



Fig. lb. 



is capable of swallowing passes belief, and the naturalist who keeps one 

 of them in confinement is often astonished to find, sooner or later, quite 

 a collection of shells in the dish, all of which had been concealed in the 

 huge stomach of the starfish. Hamann f counted at one time ten Fccten, 

 six TeUinciy several Conus, and five Dentalium. 



In the second group of starfishes (Fig. lb) the arms are far from 

 being so conical in shape, but are more or less cylindrical; indeed in the 

 immediate neighbourhood of the body they are somewhat smaller than a 

 little further off, and hence no true body exists. The members of this 



* AstrojKctcn irregularis may be taken as the representative of this gi'oup in British 

 seas. E. J. A. 



t Hamann, 0., Bcitrdge zur Histologic dcr Echinodcrmen. Heft 2. "Die Asteriden 

 auatomisch uud liistulogisch untersucht." Jcua. G. Fischer, Svo., 1885. 



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