179 



become discernible. The upper epaulettes appear. Slightly later, the lower 

 epaulettes appear, which are situated in the lower part of the larval body. At 

 this stage, three larval pedicellariae form, one between the lower epaulettes 

 and the other two on the dorsal and ventral sides of the larval body. By the 

 end of the pluteus III stage, the larva has accumulated crimson pigment, 

 which is initially evenly distributed over the entire body. This pigment gradu- 

 ally concentrates at the tips of the arms and in the region of formation of the 

 definitive test, which develops in the amniotic sac on the left side of the 

 larval body. The stomach becomes bright green. The length of the larva 

 reaches 900 |j,m before metamorphosis (Figure 131). 



Figure 131: Strongylocentrotus nudus. 

 Pluteus III stage, 

 as — amniotic sac; lap — lower epaulettes; p — pedicellariae; uep- 



■upper epaulettes. 



Ecology 



The larvae of S. nudus appear in the plankton of Peter the Great Bay in 

 the middle ten days of July when the water temperature in the surface layer 

 is 18.5°C. The pluteus I stage is found up to August 20th. At August end, the 

 pluteus III stage can be seen undergoing metamorphosis. By mid-September, 

 the larvae of S. nudus have disappeared from the plankton, although in some 

 favorable years they are seen up to the end of September. According to Fuji 

 (1960a, b), spawning of 5. nudus in southern Hokkaido is observed from mid- 

 August to mid-December. 



