75 



Figure 52: Hinge of right valve of the veliconcha of Mytilus trossulus. 



masse at the end of August (Kulikova, 1975). Thus, during the reproduction 

 of M trossulus in the study area, the water temperature varies from 8 to 23°C. 



CRENOMYTILUS GRA YANUS (DUNKER) 



(MytUidae) 



Veliconcha 



The shell is equivalve and longitudinally oval. The anterior end is longer 

 than the posterior and only slightly drawn dorsally. The umbones are broad, 

 massive, and round (Figure 53 A, B). The larva is yellowish-brown; the umbo 

 is more intensely colored. Striation of the shell is concentric, barely percep- 

 tible. The length of the provinculum is greater than the length of the umbones. 

 The number of provincular teeth increases as the larva grows. In a developed 

 larvae the provinculum has up to 20-25 central denticles and 10 large lateral 

 teeth. The ligament is oval and located at the end of the row of denticles. The 

 larva attains the veliconcha stage at a shell length of 120-130 |im and a hinge 

 line length of 90 )xm. As the larva grows, the length of the provinculum 

 increases to 150 fi,m. Eyes appear in the larva at a shell length of 220 \x.m.. The 

 diameter of the eyes is 15 |a.m. The foot is fully formed and becomes functional 

 in the larva at a shell length of 250 |4.m. 



Larvae of C. grayanus differ from those of the Pacific mussel Mytilus 

 trossulus and Modiolus difficilis primarily in shape of the shell. Compared to 

 M. trossulus, the shell is shallower dorsoventrally and the provinculum bears 

 a larger number of denticles. C. grayanus differs from the larvae of Modiolus 

 difficilis mainly in having a wider and rounder anterior margin, a more fragile 

 shell, less distinct concentric striation, and a lighter color. 



