Wild Harris How does a Limpet Grow it's Shell to Fit the Rock it Lives on?

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A limpet shell is a perfect fit to the rock it is attached to - it has to be otherwise there would be gaps round the edge. This is achieved by the animal always returning to the same place when the tide goes out - it only fits in one particular place. If you remove a limpet and replace it somewhere else the chances are it won't be able to find its way 'home' and will probably die. The perfect fit is achieved by the animal grinding its shell against the rock on which it sits. If the rock is soft, it will create a shallow hole in which the shell fits. Harris rock is too hard however; the grinding action wears the shell instead until the edges of the shell perfectly match the rock surface. You can see limpets moving about and grazing in rock pools - if the pool has a thin carpet of sand you can see the track made as it moved along.

Limpet (Photo: Paul Tyler)

Although the rock has a rough and uneven surface, this limpet fits it perfectly.

by Paul Tyler

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