Reptiles swagger around, encircling the Parisian (7)
I believe the answer is:
turtles
'reptiles' is the definition.
(turtle is a kind of reptile)
'swagger around encircling the parisian' is the wordplay.
'swagger' becomes 'strut' (synonyms).
'around' is a reversal indicator.
'encircling' indicates putting letters inside.
'the parisian' becomes 'le' (definite article in French).
'strut' in reverse letter order is 'turts'.
'turts' placed around 'le' is 'TURTLES'.
(Other definitions for turtles that I've seen before include "Let rust settle on sea-creatures" , "Marine reptiles" , "The reptiles are let rust" , "Slow swimmers" , "Reptiles with bony shell and flipper-like limbs" .)