Aquatic creature switching ends of beautiful shore (7)

I believe the answer is:

bolster

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'shore' is the definition.
(I know that bolster is a type of shore)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for bolster that I've seen before include "Shore up" , "Extended pillow" , "Support; long pillow" , "Provide reinforcement" , "Lobster (anag.)" .)

I've seen this clue in The Independent.

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