Snaky swimmers (4)
I believe the answer is:
eels
'snaky swimmers' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eels that I've seen before include "Abstract nineteen sixties style" , "Devious types" , "Sea snakes among lees" , "Long fishes" , "Snakes found in lees" .)