251 



Figure 196: Stichopus japonicus. 

 Pentactula. General view of the larva. 



fertilization to settling at a water temperature of 2 1 °C is 1 6—20 days. Spawn- 

 ing, as in Vostok Bay, continues from June to August. Kinosita (1938) also 

 reported these periods for Hokkaido, Tanaka (1958) reported for southern 

 Hokkaido that spawning of the trepang begins at the end of June. In other 

 parts of Japan the trepang may begin spawning in mid-May (Mitsukuri, 1903) 

 and even in mid-March (Choe, 1962). 



JAPANESE CUCUMARIA 

 CUCUMARIA JAPONICA SEMPER 



Eggs large, dark green, rich in yolk, 450 |Lim in diameter. They are found in 

 the plankton at a water temperature of 11°C. The blastula forms at the end 

 of the first day of development and is oval in shape. The gastrula develops 

 two days after fertilization. It is slightly flattened dorsoventrally. Like the 

 blastula, the gastrula is also entirely covered with short cilia. Both the blas- 

 tula and the gastrula swim in the surface water layer, rotating around their 

 axis with the animal pole directed forward. 



