98 



Figure 62: Right valve of the veHconcha of Mya Japonica. 



coast of Japan (Yoshida, 1938). Larvae attain the veliconcha stage at a shell 

 length of 150 ^im and a hinge line of 50-70 |4.m. 



Ecology 



In Sakhalin (Aniva Bay, Sea of Okhotsk), the spawning period of M. 

 Japonica is protracted, beginning in early July and ending at the terminating 

 end of August or early September. The major part of the M. japonica popu- 

 lation usually spawns in Busse Lagoon (Aniva Bay) in July— beginning of 

 August. Spawning commences at a temperature of 14-15°C and larvae are 

 present in the plankton at a water temperature of 15-22°C. In Vostok Bay, 

 larvae of M japonica are found in the plankton during June -July at tempera- 

 tures of 14-22°C. 



Data on the morphology and ecology of larvae of this species are available 

 in the works of Yoshida (1938, 1953). 



TRUNCATE MYA, MYA TRUNCATA (LINNAEUS) 



(Myidae) 



Veliconcha 



The larva of Mya truncata is identical to that of M. japonica, both in 

 structure of hinge system and presence of dark pigmented bands along the 

 shoulder as well as the mantle margin. The only noticeable difference between 

 these two species is the larger size of the M. truncata larvae (90-320 |im) and 

 significant elongation longitudinally (see Figure 45). 



