177 



a single fenestrated plate at the base of the larva. In Scaphechinus mirabilis 

 the single plate is not formed but the basal and secondary rods are fused in 

 pairs. In Scaphechinus griseus these rods are not fused, only contiguous. 



Three species are found in Peter the Great Bay: Echinarachnius parma, 

 (Echinarachniidae), Scaphechinus mirabilis, and S. griseus, (Dendrasteridae). 



Descriptions of the larvae are available iov Echinarachnius parma (Fewkes, 

 1893; Kryuchkova, 1976), Scaphechinus mirabilis (Kryuchkova, 1976), and 

 Scaphechinus griseus (Kryuchkova, 1976). 



Loveniidae 



The larva has six pairs of arms and an aboral rod. The rods of the postoral 

 and posterodorsal arms as well as the aboral rod are fenestrated. In the pluteus 

 II stage the base of the aboral rod enlarges and assumes the shape of an 

 inverted arch with a long process in the middle. Fenestration in the aboral rod 

 commences from its base. 



One sea urchin of this family is found in Peter the Great Bay, namely, 

 Echinocardium cordatum. 



The larvae have been described by Selenka (1880), McBride (1914, 1918), 

 and Kryuchkova (1976). 



STRONGYLOCENTROTUS NUDUS AGASSIZ 



( Strongylocentrotidae) 



Eggs of the mature female before they are shed in water are perfectly spheri- 

 cal, nontransparent, and grayish. Their size varies from 90 to 100 |im in 

 diameter. The fertilization membrane begins to separate 2-3 min after pen- 

 etration of a spermatozoon. The first division occurs 40 min later at a tem- 

 perature of 20-2 rC. The free-swimming blastula develops after 32 hrs and 

 the pluteus I stage develops two days after fertilization. 



Pluteus I stage 



The larva is transparent, with a slightly bluish tinge. The endoskeleton is 

 visible through the tissue and is composed of simple rods. At this stage, the 

 larva has two pairs of arms: anterolateral and postoral. The body is supported 

 by thickened basal rods which, at the basal end, are somewhat flattened and 

 bear large spines that interlock the rods. Short inner transverse rods arise from 

 the site of fusion of the postoral and basal rods. Secondary basal rods are 

 attached to the inner transverse ones, they are shorter and do not fuse with 

 each other. The length of the larva at this stage is 200-400 um (Figure 129). 



