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.
Supplementary Table 1
Specimens examined, habitat and measured values of parameters: M = marine species; F = freshwater species; L = land species; SUM = Shizuoka University; SHIN = Shinshu University; BPBM = Bishop Museum; SPMN = Network for Shizuoka Prefecture Museum of Natural History; UMUT = University Museum, University of Tokyo.
Table_without_sp Supplementary Table. 1.pdf
Supplementary Table 2
Lists of repeated measurement of the Raup’s parameter. These lists were obtained from 30-repeated measurement of each specimen.
Table_without_sp Supplementary Table. 2.pdf
Supplementary Table 3
Statistics for each the Raup’s parameter of each specimen: Min = minimum; Q1 = lower quartile; Q3 = upper quartile; Max = maximum; SD=standard deviation; CV=coefficient of variation.
Table_without_sp Supplementary Table. 3.pdf
Supplementary Figure 1
Three-dimensional contour diagrams depicting the postural stability (1/Λ) and the available space for soft-body (E) values on the Γ-Δ apertural inclination morphospace for various combinations of the translation rate T and umbilical width D (for the whorl translation rate W = 100.2). The positions of actual specimens with parameters close to the values depicted on the diagrams are plotted by symbols representing their respective habitats (land, freshwater, and marine). The criterion for including a specimen on the diagram is that the measured parameters (W, T, and D) fall within a certain range of the plotted values ( , Ts, and Ds), such that W = , T = Ts ± 0.5, and D = Ds ± 0.1.
supplementary_fig_1.pdf
Supplementary Figure 2
Contour diagrams of 1/Λ (above) and E (below) on the same morphospace shown in Supplementary Figures 1, but with a whorl translation rate of W = 100.6 (see Supplementary Fig. 1 for details.)
supplementary_fig_2.pdf
Supplementary Figure 3
A, B. Nerita chamaeleon (interim number 700). C, D. Terebra areolata (interim number 2141). E, F. Achatina fulica (interim number L-288). G, H. Acavus haemastoma (interim number L-523). I, J. Aegista vermis (interim number L-93). A, C, E, G, and I. Model parameters are determined from measurements of specimens viewed from lateral (A, C, E, G, and I) and umbilical (B, D, F, H, and J) perspectives. All scale bars, 2 cm.
supplementary_fig_3.pdf
Supplementary Figure 4
Box and whisker diagrams of each ’of Raup’s parameters. These plots summary sample minimum (Min), lower quartile (Q1), median, upper quartile (Q3), and sample maximum (Max). Black cross (×) indicates the mean of sample.
supplementary_fig_4.pdf