69 



Mytilus trossulus Gould (see below), Mytilus coruscus Gould (larvae not 

 described), Crenomytilus grayanus (Dunker) (see below). Modiolus difficilis 

 (Kuroda and Habe) (see below), and Muculista senhousia (Benson) (see below) 

 inhabit Peter the Great Bay. 



Arcidae 



In shape, presence of eye spots, and structure of the lock, the larvae of the 

 family Arcidae are very similar to the larvae of the family Mytilidae, more 

 particularly to the Pacific mussel, Mytilus trossulus, and Gray's mussel, 

 Crenomytilus grayanus. They differ mainly in that the larvae of the family 

 Arcidae have a broader anterior margin and do not bear denticles in the center 

 of the hinge line. The larvae of mussels are also more elongated and their 

 umbones are less massive. 



Boucard's area. Area boueardi Jousseaume, lives in Peter the Great Bay; 

 larvae described below. 



Lithophagidae 



The shell is equivalve, longitudinally oval, and its ventral margin parallel to 

 the hinge line. The length of the shell is much more than its height. The 

 umbones are large, broad, and round. The hinge system is similar to that in 

 the family Mytilidae, but teeth in the central part of the provinculum are 

 lacking. The ligament is posterior. The shell is strong, with distinctively raised 

 growth striae. Large dark ocular spots are present. 



Adula faleatoides Habe inhabits Peter the Great Bay (see below). 



Ostreidae 



The veliconcha is large. The shell is inequivalve. The left valve is much larger 

 than the right, more convex, and has a high umbo. The right valve is flat and 

 has a low umbo. The anterior margin is more drawn out compared to the 

 posterior.The hinge comprises two anterior and one to three posterior rectan- 

 gular teeth. The space between the anterior and posterior teeth is smooth. The 

 lateral hinge system is absent. The ligament is posterior. Eyes are present and 

 visible at a shell length of 250-290 )j.m. In the mature veliconcha, dark 

 pigmentation is perceptible in the subumbonal region. 



Crassostrea gigas (Thunberg) inhabits Peter the Great Bay (see below). 



