Hair On Shells
The periostracum of the shells of most Trochulus species has hair-like features. Some of the hair-less species do possess hairs as juveniles. Hairy shells appeared to be the ancestral character state in the genus Trochulus, a feature which has most probably been lost three times independently.
These losses were correlated with a shift from humid to dry habitats, indicating an adaptive function of hairs in moist environments. It had been previously hypothesised that these costly protein structures of the outer shell layer facilitate locomotion in moist habitats. Experiments by Pfenninger et al. (2005) showed an increased adherence of haired shells to wet surfaces. The possession of hairs facilitates the adherence of the snails to their herbaceous food plants during foraging, when humidity levels are high. The absence of hairs in some Trochulus species could thus be explained as a loss of the potential adaptive function linked to habitat shifts.
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