Uncommunicative creature? (4)

I believe the answer is:

clam

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'creature?' is the definition.
(clam is a kind of creature)

I don't understand how the remainder of the clue works.

(Other definitions for clam that I've seen before include "Quahog" , "shy person" , "reticent person" , "Burrowing marine mollusc living in sand or mud" , "Proverbially reticent marine mollusc" .)

I've seen this clue in the Evening Standard.

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