Gastropods are the largest and the most diversified taxon in the phylum Mollusca. Commonly known as snails and slugs, gastropods are able to live in remarkably diversified habitats through a wide range of adaptation over time. Their shells form an important component for their adaptation because most of them protect their body from physical, physiological, and ecological perturbations with their shells.
In this talk, I will show two different theoretical approaches for understanding a morphological diversity of gastropod shells. First approach is an example of ultimate explanations of a morphological diversity of gastropod shells. Although shells of gastropods are important component for their adaptation, the shells can become a burden to them because they need to form and bring their shells. I assessed these constraints as efficiency of shell construction and shell balance, respectively. Biomechanical analysis showed that these two functions of shells are conflict in each other in terms of shell height and umbilical width. Most of actual specimens show moderate forms, which do not have extremely ill balanced or inefficient shells. Moreover, the biometric results suggest that land snails are more highly constrained than marine species in achieving a balance between shell balance and efficiency of shell construction.
Second approach focuses on an aspect of proximal explanations. The shell is formed through an accretionary growth which the epidermis of the mantle secretes shell materials little by little. Most of gastropod shells coil spirally due to asymmetric growth along inner and outer lip of an aperture. I propose a method to quantify such growth pattern along an aperture from actual specimens, and a comparability of the growth pattern with experimental data.