The marrow’s taken from terrestrial invertebrates (10)

I believe the answer is:

earthworms

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'invertebrates' is the definition.
(earthworm is a kind of invertebrate)

'the marrow's taken from terrestrial' is the wordplay.
'the marrow's' can be anagrammed to 'EARTHWORMS'.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Another definition for earthworms that I've seen is " Creatures".)

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

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