187 



Figure 139: Scaphechinus mirabilis. 



Pluteus II stage. Structure of the larval skeleton. 



sint — secondary inner transverse rod; da — dorsal arch. 



Remaining legend same as in Figure 107. 



SCAPHECHINUS GRISEUS (MORTENSEN) 



(Dendrasteridae) 



The development of this and the preceding species has not yet been described 

 by other authors. Sometimes the older individuals of S. griseus are easily 

 confused with the juveniles of Echinarachnius parma because their size and 

 color are almost identical. The only distinguishing feature in such cases is the 

 position of the anal opening, which in S. griseus lies on the aboral side of the 

 test. 



Mature eggs in S. griseus are 90—100 |J.m in diameter but unlike in 5'. 

 mirabilis and E. parma, the secondary egg membrane is not visible. At a 

 temperature of 20-2 1°C, development proceeds at the same rate as in E. 

 parma. Thus, the blastula appears 16 hrs and the gastrula 24 hrs after fertili- 

 zation. The early pluteus develops 36 hrs after penetration of the egg by the 

 spermatozoa. 



