84 



SWIFTOPECTEN SWIFTI (BERNARD) 

 (Pectinidae) 



Veliconcha 



The maximum length of the larval shell is 240-250 |im and the length of 

 the hinge line 120—130 fxm. The shell is triangular and the valves are convex. 

 The anterodorsal margin slopes sharply downward. The umbones are high and 

 acute. The larval shell is stout and richly colored. Radial striation is indistinct, 

 while concentric striation is distinct. A broad marginal band is visible along 

 the entire edge of the shell. The hinge line in a developed larva has up to seven 

 large marginal teeth. The ligament is median and slightly shifted toward the 

 anterior margin (Figure 56). 



Ecology 



Larvae of this scallop are found en masse in the plankton of Busse Lagoon 

 (southern Sakhalin) and Peter the Great Bay during August— September at a 

 surface water temperature of 15-20°C. Typically, these larvae are dominant 

 near-bottom at depths of 10—20 m. 



The morphology of larvae of Swiftopecten swifti has been described by 

 Kulikov, Medvedeva and Guida (1981). No data on the ecological develop- 

 ment of this species were found in the literature. 



MIZUHOPECTEN YESSOENSIS (JAY) 



(Pectinidae) 



Veliconcha 



The larval shell is 260—270 \\ia long and the provinculum 100—110 |J.m 

 long. The veliconcha shell of the Primorsk scallop is triangular-ovate. The 

 anterior margin is short, round, and sharply drawn dorsally. The anterodorsal 

 margin is longer than the posterior and almost straight due to the highly raised 

 anterior end. The posterodorsal margin slopes sharply downward and gradually 

 merges with the posterior margin of the shell. The umbo is small, round, and 

 slightly raised over the hinge line. The larva is almost colorless and transpar- 

 ent. The shell is brittle, with distinct concentric and radial striations. The hinge 

 is of the taxodont type, bearing rectangular teeth along the margins of the 

 provinculum. A well-developed larva has five teeth on each side of the hinge 

 row (see Figures 38 and 57). 



