Crossword Genius

Greek primate's eaten shellfish (5)

Ross

I believe the answer is:

gaper

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'eaten shellfish' is the definition.
The definition suggests a singular noun which matches the answer.

'greek primate's' is the wordplay.
'greek' becomes 'g' (philological abbreviation).
'primate's' becomes 'aper' (I can't explain this - if you can you should give a lot more credence to this answer).
'g'+'aper'='GAPER'

Can you help me to learn more?

(Other definitions for gaper that I've seen before include "Fish; burrowing mollusc" , "one staring in wonder" , "one visibly amazed" , "who yawns?" , "Anglerfish" .)

I've seen this clue in The Guardian.
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