Lampreys (4)
I believe the answer is:
eels
'lampreys' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eels that I've seen before include "Devious types" , "Snakes found in lees" , "Slippery creatures" , "They have long bodies and very small fins" , "Slender fishes" .)