Creature turned upside down (6)

I believe the answer is:

turtle

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'creature' is the definition.
(turtle is a kind of creature)

I don't understand the rest of the clue.

(Other definitions for turtle that I've seen before include "See 7" , "Reptile - (kind of) dove" , "Neckline and reptile" , "that flies in 2nd" , "Marine reptile with shell" .)

I've seen this clue in the Evening Standard.

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