Bivalve shells serve as mechanical armor and enable behaviors such as swimming and burrowing to escape predators. Thus, shell shape plays a critical role in a bivalve’s ability to defend against attacks from predators like shell-crushers. The shapes of bivalve shells converge on a select few morphologies which correlate with life mode and motility. Additionally, shell shape is believed to be related to shell strength. Here, mathematical modeling and 3D printing were used to analyze the protective function of different shell shapes against vertebrate shell-crushing predators. Considering the life modes different shell shapes permit and analyzing their strength in bulk compression provides insight to evolutionary and ecological tradeoffs with respect to mechanical and behavioral defenses. These empirical tests are the first of their kind to isolate the influence of bivalve shell shape on strength and quantitatively demonstrate that shell strength is derived from multiple shape parameters. This theoretical study demonstrates results consistent with examples of shell shapes which allow escape behaviors being mechanically weaker than those which do not. Additionally, shell elongation from the umbo, a metric often overlooked, is shown to have significant effects on shell strength.