Polyaspartate is a biopolymer in oysters that stops growth of shells by inhibiting growth of excess calcium carbonate.

References

Polyaspartate is a biopolymer produced by oysters to help mold their shells into their characteristic shape. Polyaspartate stops excess growth of calcium carbonate, the principal constituent of oyster shells. (Ashley 2002:32-33)

Journal article
It's Not Easy Being GreenSci AmDecember 16, 2002
Steven Ashley

Journal article
Control of Calcium Carbonate Nucleation and Crystal Growth by Soluble Matrx of Oyster ShellScienceOctober 5, 2006
A. P. WHEELER, J. W. GEORGE, C. A. EVANS

Living System/s

Organism
True OystersOstreidaeFamily