Regressive pests grope around for marine creature (8)

I believe the answer is:

starfish

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'marine creature' is the definition.
(I know that starfish is a type of marine creature)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for starfish that I've seen before include "Marine creature with five arms" , "One found at sea" , "Marine echinoderm" , "Five-armed sea creature" , "Asteroid (in the sea)" .)

I've seen this clue in The Irish Times.

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