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）视角探究腹足类壳体（gastropod shell）的形态多样性，重点关注壳体形态与姿势稳定性、软体组织可用空间的关联，并分别通过力矩（moment of force）计算与软组织占比（soft-tissue ratio）计算对二者进行量化评估。计算机模拟结果显示，姿势稳定性与软体组织可用空间之间存在功能权衡：螺塔（spire）低矮、脐孔（umbilicus）狭小的紧凑壳体具备较高的姿势稳定性；而螺塔高耸、脐孔宽大、壳层重叠度较低的壳体则拥有更大的软体组织可用空间。基于理论模型开展的功能形态空间分析（functional morphospace analysis）表明，壳口（aperture）向外且向下倾斜可缓解这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性。可实现该兼容性的理论最优壳体形态，与基于359种现生腹足类物种（extant gastropod species）估算得到的形态分布范围相符。生物测量结果还显示，陆生蜗牛（land snails）在平衡姿势稳定性与软体组织可用空间方面，所受约束程度高于海洋物种（marine species）。