176 



20(21). Basal and secondary basal rods form a basket. Single fenestrated 



plate present under the basket 



Echinarachinus parma, pluteus I stage (Figure 135). 



21(20). Basket different in shape. 



22(23). Basal and secondary basal rods fused in pairs, forming two plates 



with numerous spines on the lower side 



Scaphechinus mirabilis, pluteus I stage (Figure 138). 



23 (22). Distal ends of the basal and secondary basal rods thickened, bearing 



numerous spines, but not fused 



Scaphechinus griseus, pluteus I stage (Figure 141). 



24(19). Three-four pairs of arms. 



25 (26). Basket height three-fourths basal width. Angle of bending of the 



dorsal arch 180° 



.Scaphechinus mirabilis, pluteus II and III stages (Figures 139, 140). 

 26(25). Basket height greater than basal width. Angle of bending of the 



dorsal arch 120°. 

 27(28). Red pigment at ends of arms 



Echinarachnius parma, pluteus II or III stage (Figures 136, 137). 

 28(27). Larva light green 



. . Scaphechinus griseus, pluteus II or III stage (Figures 142, 143). 



CHARACTERS OF LARVAE ACCORDING TO FAMILIES 



Strongylocentrotidae 



The larva has four pairs of arms. All the skeletal rods are simple. The basal 

 rods are clavate. In S. nudus and S. franciscanus the basal rods bear numerous 

 spines at their ends, which interlock the rods. Secondary basal rods are also 

 present but only in S. nudus and S. franciscanus. In the pluteus III stage the 

 ends of the basal rods are reduced and the base of the larval body is broad- 

 ened. Upper and lower epaulettes appear. In S. nudus and S. franciscanus 

 pedicellariae are present. 



Three species of the genus Strongylocentrotus are found in Peter the 

 Great Bay: S. nudus, S. intermedius, and 5'. pulchellus. Descriptions of the 

 larvae are available for S. nudus (Kawamura, 1970; Kryuchkova, 1976), S. 

 intermedius (Kawamura, 1970; Krychkova, 1976), and S. pulchellus 

 (Kryuchkova, 1976). 



Scutellidae, Dendrasteridae and Echinarachniidae 



The larva has four pairs of arms. The rods of the postoral and posterodorsal 

 arms are fenestrated. The basal and secondary basal rods are fused, forming 



