Evolution encourages diversity, allowing Nature to solve problems in more than one way. This image is a 3D CT scan of a clam and a whelk, both alive. The clam (left) is nestled comfortably in the bottom half of its shell. Note the simplicity of the hinge design in its bivalve shell. By closing the shell rapidly, the clam is able to fence off a potential attack. Yet the whelk's shell (right) is even more amazing. The sophisticated spiral construction is astonishingly complex and strong, an architectural marvel by itself and an evolutionary success! Once the whelk slipped back into the spiral tunnel of its shell, the shell provides protection similar to a fortress. Both the clam and the whelk solve the vital problem of self defense, albeit in different ways. The whelk however has the upper hand because it has the ability to drill a hole directly through the clam's shell by softening it with secretions and then consumes the clam as meal.
This image earned an honorable mention.
Dr. Kai-hung Fung, Pamela Youde Nethersole Eastern Hospital (Hong Kong)