PHYLUM ECHINODERMATA 



175 



at their bases. On that surface of the central disc which is 

 directed upwards in the natural position of the animal, is in 

 the centre the mouth and on one side the anus. On the 



opposite surface are attached whorls of slender curved cy- 

 lindrical appendages, the cirri, by means of which the 

 animal is able to anchor itself temporarily to a rock or a 

 seaweed. The arms are long, flexible and tapering, shaped 



