Nematode or fluke, eg (4)
I believe the answer is:
worm
This clue is a double definition.
'nematode' is the first definition.
(thesaurus)
'fluke eg' is the second definition.
(I know that fluke is a type of flatworm)
(Other definitions for worm that I've seen before include "Screw thread; maggot" , "Vermiform wriggler" , "Slimy invertebrate with a long thin body" , "Wriggly creature" , "Wriggle" .)