173 



amp 



Figure 127: Development of primordium of Heliocidaris erythwgramma (Kaestner,* 1963). 



A — early larva; B — late larva. 



am — amniotic sac; amp — ambulacral podia. 



Figure 128: Development of Asthenosoma ijimai (Amemiya and Tsuchiya, 1979). 

 A — blastula; B — 4-day-old larva; C — 14-day-old larva; D — same, aboral view; 



E — juvenile, 

 a — arms; amp — ambulacral podia; sp — spine of interambulacral plates; tp — terminal 



podia. 



presence of an endoskeleton consisting of rods, which differ in structure in 

 different groups of these animals. These rods may fuse or simply be contigu- 

 ous. Rods proceeding from the esophagus and descending to the edge of the 

 body of the larva are called basal and usually comprise one pair. In addition 

 to these rods, in some species of sea urchins there may be one or two more 

 pairs extending parallel to the basal rods and often joining them. These are 

 the secondary basal rods. From the basal as well as secondary basal rods, 

 transverse rods are directed inward. These may be in two pairs, anterior and 

 posterior, and both pairs may not be present simultaneously in every species. 



