One giving help over a form of parasite (5)
I believe the answer is:
redia
'form of parasite' is the definition.
'redia' can be an answer for 'form' (I have seen 'Form of flatworm' mean 'redia' so perhaps 'form' could also mean 'redia'). I am not sure about the 'of parasite' bit.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for redia that I've seen before include "Life form" , "parasitic larva" , "Form of flatworm" .)