Tidal and Seasonal Patterns in the Chondrophore of the Soft-Shell Clam Mya arenaria

Thin sections of a compact, internal structure projecting from the hinge region of the bivalve Mya arenaria reveal the presence of tidal and seasonal patterns. This is the first demonstration that microgrowth increments are formed in a stucture not associated with the growing edge of the shell. The clarity and simple orientation of these extensive patterns, combined with the hinge region to disturbance and damage, suggests that detailed examinations of internal shell structures will prove valuable in ecological, archaeological, and paleoecological studies.