Crossword Genius

In a zoo you may see one close up (4)

Ross

I believe the answer is:

seal

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

'one close up' is the definition.
(I've seen this before)

'in a zoo you' is the wordplay.
I cannot really see how this works, but
'a' is present in the answer.
The remaining letters 'sel' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'may see' acts as a link.

Can you help me to learn more?

(Other definitions for seal that I've seen before include "Secure; aquatic animal" , "A mammal; one that secures" , "Authorise - plug" , "Sea-dweller can produce a wax impression" , "Stick down" .)

I've seen this clue in The Globe and Mail.
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