Maintain one shed offers marine life (4)

I believe the answer is:

clam

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'life' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Perhaps you can see a link between them that I don't see?

I don't understand the remainder of the clue.

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(Other definitions for clam that I've seen before include "Shellfish - secretive person" , "Proverbially reticent marine mollusc" , "shy person" , "Mollusc with firmly-closed shell" , "Mollusc with tightly-closed shell" .)

I've seen this clue in the Sydney Morning Herald.

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