Oops!  In my last post, the line:

Bivalves which live in shallow water, in climates which fluctuate
between frigid and warm, may have true annular growth rings . . .

should have read:

Bivalves which live in shallow water, in climates which fluctuate
between frigid and warm, may have true ANNUAL growth rings . . .

All growth rings are annular (ring-shaped), but not all are annual (yearly).

Paul M.