180 



STRONGYLOCENTROTUSINTERMEDIUS (AG ASSIZ) 



(Strongylocentrotidae) 



The mature eggs of this species are smaller than those of S. nudus; 

 their diameter does not exceed 90 (im. The eggs are nontransparent and 

 grayish. The fertilization membrane appears 5 min after penetration by the 

 spermatozoa. The first division occurs 45—50 min after fertilization at a 

 temperature of 20— 21 °C. The pluteus I stage develops two days later. 



Pluteus I stage 



The larval body is transparent, slightly bluish, with evenly scattered 

 granules of crimson pigment. The basal part of the body is highly elongate 

 and contains the basal rods whose ends are clavate. One of the rods terminates 

 with a small depression while the other bears a spine that fits into this 

 depression. Secondary basal rods are absent. The inner transverse rods are 

 very short. The rods supporting the anterolateral and postoral arms are two- 

 thirds of the length of basal rods. The larva at this stage is 250—400 ^im long 

 (Figure 132). 



Figure 132: Strongylocentrotus intermedins. 



Pluteus 1 stage. 



A — general view of the larva; B — basal rods. 



Legend same as in Figure 103. 



Figure 133: Strongylocentrotus intermedius. 



Pluteus II stage. 



da — dorsal arch. 



Remaining legend same as in Figure 107. 



