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Gastropod Main
Glossary
References
Links
Hooper Main |
Evolution 5
In an example of convergent evolution, the land slugs have also lost their shells like their opisthobranch cousins. Snails that have adapted to constantly wet areas, like tropical or temperate rainforests, no longer needed to retreat into their shells in order to escape dry periods. This, combined with a lack of available calcium for shell building in these wet climates, has led to an evolutionary predilection in land snails for smaller and smaller shells. Instead of shells, these terrestrial pulmonates (such as slugs) rely on distasteful chemicals in their slime or other means to ward off predators. In many ways the slug represents the apex of gastropod evolution.
Figure 6: A common garden slug from Britain. In spite of the loss of a shell, slugs are quite successful and abundant.
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