74 



yellow to brown), especially in the umbonal region. Eyes are absent. A mar- 

 ginal band passes along the edge of the shell. The posterior adductor is larger 

 than the anterior. The latter undergoes considerable reduction during larval 

 development while the posterior adductor grows continuously. 



Teredo navalis Linne (see below), Bankia setacea (Try on) (see below), 

 and Zachsia zenkewitchi Bulatoff and Rjabtschikoff (larva described by Temer 

 and Yakovlev, 1981) inhabit Peter the Great Bay. 



PACIFIC MUSSEL, MYTILUS TROSSULUS GOULD 



(Mytilidae)* 



Veliconcha 



The shell is triangular-oval, its anterior end tapering and raised. The 

 anterior shoulder is longer than the posterior, but just slightly. The umbone is 

 conoid but not broad (see Fig. 44). Umbones appear at a small shell length of 

 125—135 |im. The larva is weakly colored. Striation is concentric and barely 

 noticeable. Eyes appear in larvae with a shell length of 230—240 |j.m. The 

 diameter of the eyes is 5—7 |im. The hinge line is weakly bent and its length 

 more than the umbonal width, constituting 75—85 jim in the early veliconcha 

 and 140-150 |im in the late veliconcha. The early veliconcha is 130—140 |im 

 in size, with three-four large teeth in the anterior part, two-three teeth in the 

 posterior part, and 11—13 denticles in the middle. The number of teeth in- 

 creases as the larva grows, reaching 8-10 on each side of the hinge line in the 

 late veliconcha. There are 15—20 denticles in the center (Figure 52). The 

 ligament is large, oval, and posterior. Metamorphosis occurs at a shell length 

 of 250-350 |im. 



Ecology 



Spawning of the Pacific mussel extends from May to September in Peter 

 the Great Bay, Sea of Japan. Larvae appear in the plankton from June to mid- 

 September at a water temperature of 13-23°C. The maximum number of 

 larvae is found from the second half of June to mid- July (Kasyanov et al., 

 1976, 1980; Shepel', 1979). In Avachin Inlet (southern Kamchatka) late larvae 

 are found from mid- August to September at a water temperature of 8— 15°C 

 (Buyanovskii, 1987). In the waters of southem Sakhalin larvae of the Pacific 

 mussel are found in the plankton (from early August to mid-October; with 

 maximum occurring mid- August) at a water temperature of 8 20°C, settling en 



* Using the method of protein electrophoresis, it was demonstrated that this species lives in 

 the Far-Eastern seas of Russia, and not the closely related species, Mytilis edulis Linne (MacDonald 

 etal, 1990). 



