Wriggler (3)
I believe the answer is:
eel
'wriggler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eel that I've seen before include "Slender fish" , "Slippery character" , "Slithery fish" , "Proverbially slippery fish" , "Slippery type" .)