IX 



PHYLUM ECHINODERMATA 



397 



series of five radiating arras. In the natural position of the animal 

 the side of the disc which corresponds to the oral or actinal 

 surface of the Starfish is directed upwards, and the aboral or 



cir 



FIG. 335. Antedon. Side view of entire animal (From Lenckart and Nitsche's Diagram?.) 



abactinal surface downwards. The five arms are bifurcated at 

 their bases ; they are feather-like and highly flexible, acting as 

 the locomotive organs of the animal, their alternate flexions and 

 extensions resulting 

 in a slow movement 

 through the water. 

 On the aboral side of 

 the disc are whorls 

 of slender, curved, 

 cylindrical appen- 

 dages, the cirri (Fig. 

 336), by means of 

 which the Feather- 

 star is enabled to 

 anchor itself tem- 

 porarily to a rock 

 or a sea-weed. 



On the oral side 

 of the disc, the body- 

 wall is soft and 

 flexible, containing 

 only scattered irre- 

 gular Spicules of FIG. 3:56. Aboral view of Antedon. r. centro-dorsal ossicle ; 



1 cir. cirrus ; R } , R 2 , R' 1 , the three radial plates of one 



CalCareOUS matter; column ; syz. syzygy or articulation. (After MacBride.) 



