A part of morphological diversity and uniformity are occurred by geometrical and physical factors. Gastropod shell forms have been studied in terms of morphological adaptation because almost these forms show regular spiral geometry and various coiling patterns. We revealed that gastropods form their shell to balance between the postural stability and the available space for soft-body, and aperture inclination is an important character to be compatible (Noshita et al. in press). Moreover, biometric analysis found a difference of aperture inclination between habitats. Land snails have high inclination and marine species have low and it might be explained by drag of fluid. Thus, I attempted to test my hypothesis by estimating projected area of shells because drag force is usually proportional to projected area. As a result, a low-spired shell with middle inclination has a large projected area. This trend corresponds to a pattern of museum collections of marine species. Finally, I aim to get an integrated view of postural stability in terms of drag and gravity.

Noshita, K., Asami, T., Ubukata, T., (in press) Functional constraints on coiling geometry and aperture inclination in gastropods. Paleobiology.