Shell Growth in the Scallop Argopecten Irradians. I. Isotope Incorporation with Reference to Diurnal Growth.

1. Incorporation of calcium and carbonate into shell has been studied in the scallop Argopecten irradians using 45Ca and 14C-bicarbonate. 2. The incorporation of 45Ca and 14C-carbonate into shell was linear with time after a lag period of 1 to 2 hours. The shell-forming mantle tissue attained a steady state with respect to 45Ca in the sea water medium within 2 hours. 3. The molar ratio of 45Ca to 14C-carbonate deposited in shell was not significantly different from unity during 5 hours. 4. The rate of incorporation of 14C-carbonate into shell was highest at the ventral edge and extremely low in the central and hinge areas. 5. The rate of incorporation at the ventral shell edge did not change with increase in shell size. 6. The rate of incorporation of carbonate was low at night when growth ridges form and increased 3-fold at midday when growth ridges are not being formed. 7. The protein content of the shell ridges was 32.9 ± 3.9% and the protein content of the shell including ridges was 16.0 ± 2.1%.