70 



Pectinidae 



The shell is inequivalve. The left valve is slightly more convex than the right. 

 The shell is triangular and its apex coincides with the anterior end, which is 

 more acute and longer than the posterior, and produced frontally and dorsally. 

 The ventral margin slopes sharply toward the anterior end. The dorsal margins 

 are unequal, with the anterior margin usually longer than the posterior. The 

 umbones are small, round, and slightly raised. The valves are brittle, thin, and 

 colorless. The sculpture of the prodissoconch is fine and poorly visible. In the 

 developing dissoconch in the pediveliger stage, the sculpture is alate, with 

 radial ridges (veins). The taxodont hinge (provinculum) is very similar to that 

 in Mytilidae and comprises several rectangular teeth on each margin of the 

 tooth row. The number of teeth may increase as the larva grows. The central 

 part of the provinculum is so thin that no teeth whatsoever are present (in most 

 species) or the teeth are almost indistinguishable. The lateral hinge system is 

 lacking. The ligament is median or posterior. Ocular spots appear in the 

 veliconcha before metamorphosis. 



Chlamys farreri nipponensis Kuroda (see below), Swiftopecten swifti 

 (Bemardi) (see below), and Mizuhopecten yessoensis Jay (see below) inhabit 

 Peter the Great Bay. 



Hiatellidae 



The veliconcha shell is equi valve and rounded- triangular. The anterior end is 

 pointed and directed forward sharply. The umbones are round and distinct. The 

 posterior margin is obtuse and straight while the ventral margin is roundish. 

 There is a large tooth on the right valve, located in the anterior part. The left 

 valve likewise has just one provincular tooth. One flange is located on the right 

 valve and the other on the left valve. The ligament is large and posterior. Eyes 

 are absent. 



Hiatella arctica (Linne) inhabits Peter the Great Bay (see below). 



Kelliidae 



The shell is equivalve, large, flat, and roundish or slightly squared. The ante- 

 rior end is more obtuse than the posterior. The umbones are small. The 

 provincular teeth are absent. A rudimentary lateral tooth appears by the end 

 of planktonic phase. The ligament is median or anterior. The posterior muscle 

 — adductor — and growth striae become visible very late. The larva is lightly 

 colored. The liver and velum are light, yellowish-green. 



Kellia japonica Pilsbry is found in Peter the Great Bay and its larva is 

 described below. 



