How does life adapt to a gravitational environment? The outline of the terrestrial gastropod shell

Ryoko Okajima, Satoshi Chiba

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


How do several characteristics adapt to gravity while mutually influencing each other? Our study addresses this issue by focusing on the terrestrial gastropod shell. The geometric relationship between the spire index (shell height/diameter) and outline (cylindricality) is theoretically estimated. When the shell grows isometrically, a high-spired shell becomes conical in shape and a low-spired shell becomes cylindrical in shape. A physical model shows that the lowest- and highest-spired shells are the most balanced. In addition, a cone shape is the most balanced for a low-spired shell, and a column shape is the most balanced for a high-spired shell. Spire index and cylindricality measured for freshwater gastropods follow the relationship estimated by the model, whereas those for terrestrial gastropods deviate from this relationship. This translates to a high shell being more cylindrical than a flat shell, except in the case of extremely high or low shells. This suggests that the shape of the most balanced shells (lowest and highest shell heights) is constrained by coiling geometry but that relatively unbalanced shells (intermediate shell heights) do not follow a coiling geometry, as a result of adaptation to enable the snail to carry its shell more effectively.

Original languageEnglish
Pages (from-to)801-809
Number of pages9
JournalAmerican Naturalist
Issue number6
Publication statusPublished - 2011 Dec


  • Geometric constraint
  • Land snail
  • Model
  • Shell balance
  • Spire index

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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