Group inside enjoys terrific shellfish (6)

I believe the answer is:

oyster

'shellfish' is the definition.
(oyster is a kind of shellfish)

'group inside enjoys terrific' is the wordplay.
'group inside' says the answer is hidden in the clue (I've seen this in other clues).
'OYSTER' is hidden within 'enjoys terrific'.

(Other definitions for oyster that I've seen before include "Bivalve that may nurture a pearl" , "World as place of opportunity" , "Capital card" , "person unwilling to communicate" , "Edible bivalve mollusc" .)

I've seen this clue in The Telegraph.

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