No case for very large quantities! (6)

I believe the answer is:

oceans

I'm a little stuck... Click here to teach me more about this clue!

'quantities' is the definition.
(ocean is a kind of quantity)

'no case for very large' is the wordplay.
'no case' can be anagrammed to 'OCEANS'.
But, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for oceans that I've seen before include "Large seas" , "Great seas" , "Atlantic, Pacific etc" , "Vast bodies of water" , "expanses?" .)

I've seen this clue in the Evening Standard.

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