Evolutionary Changes
Among proposed roles invoked the variability of shells during evolution include mechanical stability, defense against predators (evolution of shells against external attacks has been proved by nanoindentation), sexual selection and climatic selection.
The shell of some gastropods have been reduced or partly reduced during the evolution. This reduction can be seen in all slugs, in semi-slugs and in various other marine and non-marine gastropods. Sometimes the reduction of the shell is associated with predatory way of feeding.
Some taxa even lost the coiling of their shell during evolution. According to Dollo's law, it is not possible to regain the coiling of the shell after it is lost. Despite that, there are few genera in the family Calyptraeidae that changed their developmental timing (heterochrony) and gained back (re-evolution) a coiled shell from the previous condition of an uncoiled limpet-like shell.
Read more about this topic: Gastropod Shell
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