SPINULOSA 463 



(sheaves) attached to a basal button. This family includes the 

 well-known " Sun-stars," with numerous arms and a wide peris- 

 tome. There are two species found on both sides of the Atlantic. 

 Solaster papposus, with thirteen or fourteen arms and long bundles 

 of spines on the dorsal surface, which is of an orange colour 

 variegated with yellow, and S. endeca with eleven rays and shorter 

 spines and of a reddish violet colour. Rhipidaster has eight arms. 

 Some genera have, however, only five arms, as, for instance, 

 Peribolaster and Korethraster (Fig. 197). In this family there 



Fig. 197. Korethraster hispidus. x 2. (From Wyville Thomson.) 



are conspicuous " Polian vesicles " attached to the water-vascular 

 ring. 



Fam. 3. Asterinidae. Spinulosa in which the aboral skeleton 

 consists of overlapping plates, each bearing a few small spines. 

 The common British representative of this family is the small 

 Asterina gibbosa, in which the arms are short and stout and of 

 somewhat unequal length. This Starfish differs from most of its 

 allies in being littoral in its habit. At low tide on the south 

 and west coasts of England it can be found on the underside of 

 stones feeding on the Sponges and Ascidians with which they are 

 covered. Like Cribrella sanguinolenta this species has a modified 

 development. The larva resembles that of Cribrella, and the 

 larval stage only lasts about a week. Owing to the fact that 



