Offspring smaller than the pupa (3)

I believe the answer is:

pup

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'offspring' is the definition.
(pup is a kind of offspring)

I don't understand the remainder of the clue.

(Other definitions for pup that I've seen before include "Canine young" , "Small palindromic dog" , "Young of canines" , "Young seal" , "Produce litter" .)

I've seen this clue in the Evening Standard.

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