How do predator chemicals change the shell shape of young barnacles?

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A fluffy gray cat clings to the trunk of a tree, looking upward as it climbs to escape. — Avoidance behaviour Cat fleeing by upward climbing.

Young barnacles adapt their morphology in response to the presence of specific predator chemicals in their environment. While they typically develop a standard volcano-shaped armor, the presence of chemicals from a specialist gastropod predator induces them to grow in a bent shape with the opening positioned to the side.1

This bent growth pattern is an adaptive response that makes the barnacle's armor more difficult for the predator to breach. Although this morphological change is a clear example of avoidance behaviour and phenotypic plasticity, the precise biological mechanism by which these predator chemicals trigger the shift in shell development remains scientifically unclear.1