Don't start deliberately to sink a marine creature! (6)

I believe the answer is:

cuttle

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'creature' is the definition.
(cuttle is a kind of creature)

I don't understand the rest of the clue.

(Other definitions for cuttle that I've seen before include "Species of mollusc with shield-shaped body" , "Squid-like mollusc" .)

I've seen this clue in The Guardian.

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