Data from: Functional constraints on coiling geometry and aperture inclination in gastropods

We studied the morphological diversity of gastropod shell forms from the viewpoint of theoretical morphology, emphasizing the relationships of shell form to postural stability and the available space for soft body, which we assessed in terms of the moment of force and soft-tissue ratio calculations, respectively. The results of computer simulations suggest a functional trade-off between postural stability and available space for soft body: a compact shell possessing a low spire and small umbilicus exhibits high postural stability, whereas a less overlapped shell form with a high spire and large umbilicus makes available space for soft body. A functional morphospace analysis using theoretical models reveals that outward and downward inclination of the aperture moderates the functional trade-off between these parameter values and permits compatibility between stable posture and efficient shell construction. The hypothetical optimum that realizes this compatibility is consistent with the observed range of forms estimated from 359 extant gastropod species. The biometric results also suggest that land snails are more highly constrained than marine species in achieving a balance between postural stability and available space for soft body.本研究从理论形态学（theoretical morphology）视角探究腹足类（gastropod）贝壳形态的多样性，重点探讨贝壳形态与姿势稳定性、软体可利用空间的关联，分别通过力矩计算与软组织占比评估完成相关量化分析。计算机模拟结果显示，姿势稳定性与软体可利用空间之间存在功能权衡：螺塔低矮、脐孔（umbilicus）较小的紧凑壳体具有较高的姿势稳定性；而螺塔高耸、脐孔较大且壳层重叠度较低的壳体则能为软体提供更充足的可利用空间。基于理论模型开展的功能形态空间分析表明，壳口（aperture）向外且向下倾斜可缓解两类参数间的功能权衡，实现稳定姿势与高效壳体构建的兼容。实现该兼容性的理论最优形态，与基于359种现生腹足类物种估算得到的形态分布范围相符。生物计量分析结果还显示，陆生螺类在平衡姿势稳定性与软体可利用空间方面，比海洋腹足类受到更强的约束。