68 NATURAL HISTORY OF OUR SHORES 



with the star-fishes, comprises the so-called " Sea-lilies " 

 of foreign seas and the " Feather Stars." 



On our shores it is represented by but one species, the 

 lovely " Rosy Feather Star " (Antedon rosacea, or Comatula 

 rosacea). It has rays, usually ten in number, which are 

 plumelike, and it has a series of hooked claws around the 

 disc, for fastening to rocks and other objects. It is about 

 four inches across, and is usually of a deep blood-red colour. 

 It is of great interest to the naturalist, as in its young 

 stages it is quite unlike all other Echinoderms. 



The young, after their larval free-swimming stage, grow, 

 plantlike, upon a stalk, which is jointed. Then when 

 growth has advanced to a certain point the rayed flower- 

 like top breaks away and becomes of the adult form. 



The stalked stage represents an ancient type, which, 

 under the names of Encrenites and " Stone-lilies," are 

 common as fossils in our limestone rocks. In some foreign 

 representatives of the Crinoidea the stalked stage is per- 

 sistent through life. 



These forms must have been very abundant in the seas 

 which once covered what is now our land. 



The various stages are represented in Fig. 27. 



The Echinoidea, or " Sea-urchins" The members of 

 this division resemble the star-fishes in general anatomy, 

 although they are of very different outward form. 



The structural affinity can be represented by an imaginary 

 experiment. If one of the broad-rayed stars say one of 

 the " Cushion Stars " had its projections turned up over 

 the back until the points just touched, and then the edges 

 were fused together, then the once outward enclosed skin 

 be done away with, it will be seen that the five-rayed 

 system would still be maintained, and that the ambulacral 

 grooves, with their tube feet, would now extend vertically 

 up the sides of the now rounded mass. Then we should 

 have a sea-urchin. 



