175 



6. Formation of fenestrated plates in the larvae of later stages. Such plates 

 are characteristic of larvae of the Superorder Camarodonta. 



7. Length of larva: Measured from the body base to the arm tip in a 

 perpendicular plane. 



8. Angle of bending of the dorsal arch. 



Key to Species Based on Larvae in the Pluteus Stage 



1 (6). Aboral rod present Loveniidae 



2 (3). Two pairs of arms 



Echinocardium cordatum, pluteus I stage (Figure 144). 



3 (2). More than two pairs of arms. 



4 (5). Three-four pairs of arms. Transverse rod present between the basal 



rods, above the aboral rod 



Echinocardium cordatum, pluteus II stage (Figure 145). 



5 (4). Five-six pairs of arms. Transverse rod absent between the basal 



rods, above the aboral rod 



Echinocardium coiidatum, pluteus III stage (Figure 146). 



6 (1). Aboral rod absent. 



7(18). All skeletal rods simple. Strongylocentrotidae 



8(11). Two pairs of arms. 



9(10). Basal rods which processes at the distal end 



Strongylocentrotus nudus, pluteus I stage (Figure 129). 



10 (9). Basal rods clavate, one with a spine, the other with a depression. 



.... Strongylocentrotus intermedins, pluteus I stage (Figure 132). 



1 1 (8). More than two pairs of arms. 

 12(15). Three pairs of arms. 



13(14). Secondary basal rods fused above the basal rods 



Strongylocentrotus nudus, pluteus II stage (Figure 130). 



14(13). Secondary basal rods are absent. Inner transverse rods present. . . 



. . . Strongylocentrotus intermedins, pluteus II stage (Figure 138). 

 15(12). Four pairs of arms. 

 16(17). Three pedicellariae on the inner part of the arm rods; no fenestrated 



plates 



Strongylocentrotus nudus, pluteus III stage (Figure 131). 



17(16). Pedicellariae absent. Perforated plates X)n the inner part of the arm 



rods 



. .Strongylocentrotus intermedins, pluteus III stage (Figure 134). 

 18 (7). Skeletal rods simple and complex 



Echinarachniidae and Dendrasteridae. 



19(24). Tv/o pairs of arms. 



